Hormonal contraception encompasses a broad and pharmacologically diverse set of preparations whose rational use requires understanding of mechanism at each target site, the comparative pharmacokinetics of available formulations, the drug interactions that can nullify contraceptive efficacy or precipitate adverse effects in patients on concurrent medications, and the evidence base for contraindications graded by the World Health Organization Medical Eligibility Criteria (WHO MEC) for contraceptive use. This module provides the depth of pharmacological detail required to answer complex clinical questions about method selection in patients with complicating medical conditions, polypharmacy, or special reproductive contexts. The core distinction between combined and progestin-only methods, and between reversible short-acting and long-acting reversible contraceptive methods, organizes the clinical framework, while the pharmacology of emergency contraception and its mechanism-dependent time limitations closes the module.
Combined oral contraceptives (COCs) achieve contraception through three pharmacologically distinct mechanisms that reinforce one another in a hierarchical fashion. The primary and most reliable mechanism is suppression of the hypothalamic-pituitary-ovarian (HPO) axis through sustained elevation of exogenous estrogen and progestin, which eliminates the normal pulsatile gonadotropin-releasing hormone (GnRH) stimulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. Ethinyl estradiol (EE) acting on estrogen receptor alpha (ERα) in the hypothalamus and pituitary suppresses FSH, preventing follicular development, while the progestin component suppresses the mid-cycle LH surge that triggers ovulation. The net effect is anovulation in more than 99% of cycles in perfect-use conditions, with the small residual ovulation rate arising primarily from missed or late pills that allow FSH to begin follicular recruitment before the next dose restores suppression.1
The second mechanism operates at the level of the cervix: progestins thicken and desiccate cervical mucus by converting it from the spinnbarkeit, or highly fluid and penetrable, mid-cycle pattern driven by rising estradiol to a viscous, cellular, and impenetrable state. Under progestin dominance, cervical mucus forms a dense glycoprotein mesh that blocks sperm penetration with high efficiency. This mechanism is also the primary mechanism of progestin-only contraceptives at low doses, since progestins that do not reliably suppress ovulation still reliably thicken cervical mucus if taken consistently. The mucus effect is pharmacokinetically sensitive: the norethindrone (norethisterone) 0.35 mg minipill requires dosing within a 3-hour window each day because cervical mucus permeability begins to return by the fourth hour after the last dose falls below the mucus-suppression threshold.2
The third mechanism is endometrial atrophy. Sustained combined hormonal exposure produces a thin, poorly vascularized endometrium that is histologically and functionally unsuitable for implantation. The progestin component drives endometrial stromal decidualization followed by glandular atrophy with continued exposure; the estrogen component is necessary for endometrial priming and maintaining a withdrawal bleed when pills are cycled. The endometrial mechanism is considered a back-up rather than a primary mechanism, operating only if a fertilized ovum were to reach the uterus despite failure of the first two mechanisms. This pharmacological understanding is clinically relevant because it informs the threshold below which combined oral contraceptive (COC) efficacy is compromised: it is anovulation that defines the contraceptive ceiling, and any disruption to the ovarian suppression mechanism by missed pills, vomiting, malabsorption, or drug interactions produces the greatest risk of unintended pregnancy.13
Anovulation is the dominant mechanism of COCs: without ovulation there is no egg to fertilize. Cervical mucus thickening provides a robust secondary barrier. Endometrial atrophy is a tertiary back-up mechanism. For progestin-only methods that do not reliably suppress ovulation (norethindrone 0.35 mg minipill, LNG-IUD at systemic levels), cervical mucus thickening plus endometrial effects are the primary mechanisms. For the etonogestrel implant and the desogestrel 75-microgram minipill, ovulation suppression is reliable and is the primary mechanism.
Modern combined oral contraceptive (COC) formulations are characterized by the dose and identity of the estrogen component and the generation and receptor profile of the progestin component. The ethinyl estradiol (EE) dose in available combined pills ranges from 10 to 50 micrograms per day, with the majority of currently prescribed preparations containing 20 to 35 micrograms. Ultra-low-dose preparations (10 to 15 micrograms EE) produce minimal cycle control and are generally reserved for perimenopausal women seeking contraception with the least hormonal exposure. Standard low-dose preparations (20 micrograms EE) provide adequate contraceptive efficacy with the lowest venous thromboembolism (VTE) risk within the EE-containing class. Thirty-five-microgram EE preparations are used when a stronger anti-androgenic effect is desired, for example in polycystic ovary syndrome (PCOS) or acne, because higher EE doses produce greater sex hormone-binding globulin (SHBG) elevation and therefore greater reduction in free androgen levels.14
Monophasic formulations deliver a fixed dose of both EE and progestin throughout all active pills. Biphasic and triphasic formulations vary the progestin dose, and in some preparations the EE dose, across three phases of the 21-day active pill cycle, with the intent of mimicking the natural hormonal fluctuations of the menstrual cycle and reducing total progestin exposure. Clinical evidence has not demonstrated a meaningful difference in contraceptive efficacy, cycle control, or tolerability between monophasic and multiphasic preparations, and monophasic pills are generally preferred for their simplicity and the ease of managing missed pills.1
The progestin component determines the non-contraceptive pharmacological profile of the COC. Second-generation progestins, specifically levonorgestrel (LNG) and norgestrel, carry the highest androgenic index among available progestins and are associated with the most consistent epidemiological evidence for VTE risk as a class, but they provide the most established safety data for arterial thromboembolism and the lowest VTE risk among combined pills when used at low EE doses (20 micrograms). Third-generation progestins (desogestrel, gestodene, norgestimate) have lower androgenic activity and a more favorable lipid profile but are associated in multiple epidemiological studies with a higher VTE risk than second-generation formulations, attributed to differential effects on activated protein C (APC) resistance and coagulation factor profiles. The MEGA (Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis) study and a meta-analysis by Lidegaard et al. consistently demonstrated that third-generation progestin COCs carry approximately 1.5 to 2 times the VTE risk of LNG-containing pills.5
The pill containing estradiol valerate paired with dienogest (Natazia/Qlaira) uses a quadriphasic regimen and represents the first approved COC using natural estradiol rather than EE as the estrogen component. Estradiol valerate is rapidly hydrolyzed after absorption to release 17β-estradiol, producing a more physiological estrogen profile with less hepatic stimulation than EE-containing formulations. The dienogest component provides strong progestational activity with anti-androgenic properties and favorable endometrial effects. Cycle control with the estradiol valerate–dienogest pill is somewhat less predictable than standard EE-containing preparations owing to the shorter half-life of estradiol and the more complex quadriphasic regimen, and missed-pill instructions differ from standard 21/7 cycle pills.7
The estetrol (E4)–drospirenone COC (Nextstellis/Drovelis), discussed in Ova-01 with respect to estetrol pharmacology, provides a combined pill with anti-androgenic and anti-mineralocorticoid properties conferred by drospirenone, combined with the reduced hepatic stimulation of estetrol relative to EE. The Phase 3 PEARL (Pooled Efficacy and Research on LNG) trial demonstrated a Pearl Index of 0.69 per 100 woman-years and favorable bleeding control, positioning this formulation as an alternative for women seeking combined hormonal contraception with the lowest available hepatic estrogenic exposure.7
All EE-containing COCs increase VTE risk approximately 3–4-fold above the baseline non-pregnant, non-pill risk of approximately 2 per 10,000 woman-years. LNG/norgestrel (2nd generation) at 20 mcg EE carries the lowest absolute VTE risk within the EE class. Third-generation and drospirenone-containing pills carry higher relative VTE risk than LNG. The absolute excess VTE risk from any modern low-dose COC is small (approximately 5–10 extra events per 10,000 woman-years) and substantially lower than the VTE risk of pregnancy itself (approximately 29 per 10,000 pregnancies). Route matters: transdermal estradiol-based HT does not carry VTE risk elevation.
Progestin-only contraceptive methods span a wide range of delivery systems and pharmacokinetic profiles, from the short-acting norethindrone (norethisterone) 0.35 mg minipill to the 3-year subdermal etonogestrel implant, and they share the fundamental advantage of being free from the estrogen-related contraindications that apply to combined hormonal methods. All progestin-only methods are safe in women with a personal or family history of deep vein thrombosis (DVT) or pulmonary embolism (PE), known thrombophilia, migraine with aura, or age above 35 combined with smoking; these are conditions in which the World Health Organization Medical Eligibility Criteria for Contraceptive Use (WHO MEC) rates ethinyl estradiol (EE)-containing methods as Category 3 or 4.6
The norethindrone 0.35 mg progestin-only pill (POP), known as the minipill, primarily prevents pregnancy through thickening of cervical mucus rather than reliable ovulation suppression, since the 0.35 mg norethindrone dose achieves serum levels sufficient for cervical mucus effect in approximately 40% of cycles but does not consistently suppress the luteinizing hormone (LH) surge. Because cervical mucus permeability begins to recover within 3 to 4 hours after the plasma norethindrone level falls below its mucus-thickening threshold, the minipill requires ingestion within the same 3-hour window daily for reliable efficacy. Typical-use failure rates of approximately 7% to 9% per year are substantially higher than perfect-use rates of approximately 0.3%, reflecting the pharmacokinetic demand of this narrow dosing window. The desogestrel 75-microgram POP (Cerazette/Cerelle) differs in a clinically decisive way from the norethindrone minipill in that it reliably suppresses ovulation in approximately 97% to 99% of cycles by maintaining plasma etonogestrel (the active 3-ketodesogestrel metabolite) above the ovulation-suppression threshold throughout a 12-hour pill interval, providing a more forgiving missed-pill window and efficacy comparable to combined pills.27
The etonogestrel subdermal implant (Nexplanon) is a 4-centimeter ethylene vinyl acetate rod inserted subdermally in the inner upper arm that releases etonogestrel at an initial rate of approximately 60 to 70 micrograms per day, falling to approximately 25 to 30 micrograms per day by year 3. Serum etonogestrel levels remain consistently above the 90 picogram per milliliter threshold required for ovulation suppression throughout the 3-year approved duration in women of normal body weight. The implant is the most effective reversible contraceptive available, with a Pearl Index of less than 0.1 per 100 woman-years across all user categories because it eliminates adherence as a failure variable. Return of ovulation occurs in the majority of users within 3 to 4 weeks of removal. The implant does not protect against sexually transmitted infections (STIs) and is associated with irregular bleeding in approximately 20% of users in the first year, which is the leading cause of early discontinuation. Cytochrome P450 3A4 (CYP3A4) inducers accelerate etonogestrel metabolism and may reduce implant efficacy, a concern particularly relevant in women on enzyme-inducing antiepileptic drugs (AEDs) or rifampin, for whom alternative contraception should be considered.7
Depot medroxyprogesterone acetate (DMPA), administered as 150 mg intramuscularly every 12 weeks or 104 mg subcutaneously every 13 weeks, suppresses ovulation within 24 hours of the first injection and maintains contraceptive serum medroxyprogesterone acetate (MPA) levels for the full 12 to 13 week dosing interval through depot release from the injection site. DMPA is highly effective with a Pearl Index below 0.3 per 100 woman-years with perfect use. Its pharmacokinetic characteristics make it particularly robust against drug interactions because the depot MPA concentrations are substantially higher than those achieved with oral formulations, providing a buffer against CYP3A4 induction. The primary clinical concerns with DMPA are the delayed return to fertility (median 9 to 10 months after the last injection, with fertility return occasionally delayed up to 18 months), bone mineral density (BMD) reduction with prolonged use, and the association with menstrual irregularity and amenorrhea. BMD reduction with DMPA is reversible after discontinuation and does not appear to increase fracture risk in adults, though the WHO advises caution with use beyond 2 years in adolescents whose peak bone mass has not yet been achieved. DMPA is a WHO MEC Category 2 (advantages outweigh risks) in women with migraine with aura, making it usable where COCs are Category 4.67
The levonorgestrel intrauterine device (LNG-IUD) is available in several formulations delivering different total LNG loads: the 52 mg system (Mirena) releases approximately 20 micrograms per day initially, falling to approximately 10 micrograms per day by year 5; the 19.5 mg system (Kyleena) releases approximately 9 micrograms per day; and the 13.5 mg system (Skyla) releases approximately 6 micrograms per day. The primary contraceptive mechanism of the LNG-IUD is local: high LNG concentrations in the endometrium produce marked decidualization and glandular atrophy, and LNG in cervical mucus produces the same impermeability seen with systemic progestins but at much lower systemic concentrations. The 52 mg LNG-IUD suppresses ovulation in approximately 50% of cycles in the first year, with this proportion falling to less than 25% by year 5, meaning that cervical and endometrial effects rather than ovulation suppression are the dominant mechanisms after the first year. Systemic serum LNG levels with the 52 mg device are approximately 150 to 200 picograms per milliliter, well below the systemic threshold for consistent ovulation suppression and far below the levels achieved with oral LNG-containing pills, explaining why systemic progestogenic side effects are minimal with the LNG-IUD compared to oral progestin methods.878
Long-acting reversible contraceptive methods (LARCs) including the etonogestrel implant, LNG-IUDs, and the copper IUD achieve their published efficacy figures without relying on daily or coital adherence, making their perfect-use and typical-use failure rates nearly identical. For comparison: perfect-use COC failure rate is 0.3% per year, but typical-use failure is approximately 7% to 9% per year because of missed pills. Whenever a patient's circumstance makes consistent daily pill adherence uncertain, a LARC is pharmacologically superior regardless of the patient's stated intent to adhere.
Emergency contraception (EC) encompasses pharmacological and device-based interventions used after unprotected intercourse to prevent pregnancy. The three principal options differ substantially in mechanism, efficacy window, weight-dependent efficacy, and post-use contraception requirements. Levonorgestrel (LNG) 1.5 mg EC works primarily by inhibiting or delaying ovulation when administered before the luteinizing hormone (LH) surge: it suppresses the LH surge by acting on the pituitary and hypothalamus and delays follicular rupture. LNG EC has no consistent effect on post-fertilization events and is ineffective when administered after ovulation has already occurred, because its mechanism is pre-ovulatory. Efficacy is highest when taken within 24 hours of unprotected intercourse (approximately 95% reduction in expected pregnancy rate) and falls substantially when taken 48 to 72 hours after intercourse (approximately 58% reduction), defining a practical 72-hour clinical window beyond which efficacy becomes unreliable. LNG EC is widely available and does not require a prescription in most countries, reflecting its established safety profile.6
Weight and body mass index (BMI) substantially attenuate LNG EC efficacy. Pharmacokinetic studies demonstrate that serum LNG concentrations following a 1.5 mg oral dose are significantly lower in women with BMI above 26 kg/m² and become inadequate for reliable ovulation suppression at BMI above 35 kg/m², reflecting the higher volume of distribution and potentially faster metabolism in higher-weight individuals. The European Medicines Agency (EMA) updated LNG EC labeling in 2014 to note that efficacy may be reduced in women over 75 kg and that alternative methods should be considered. Ulipristal acetate (UPA) exhibits less weight-dependent attenuation than LNG in comparative pharmacokinetic studies, and the ELLA (Efficacy of Levonorgestrel Emergency Contraception and Ulipristal Acetate) trial demonstrated that UPA maintained superior efficacy to LNG at all BMI categories examined, making UPA the preferred pharmacological EC option in women with BMI above 26 kg/m².910
Ulipristal acetate (UPA) 30 mg is a selective progesterone receptor modulator (SPRM) that acts as a high-affinity partial agonist/antagonist at the progesterone receptor (PR), with tissue-selective activity determined by the coactivator environment. Its primary EC mechanism is inhibition of follicular rupture: UPA can inhibit or delay ovulation even when administered after the LH surge has begun, a capability LNG lacks. This post-LH-surge activity extends UPA efficacy to a 120-hour (5-day) window after unprotected intercourse, compared to the 72-hour window for LNG, and provides higher efficacy than LNG within the shared 72-hour window. The ELLA trial, a randomized non-inferiority study, demonstrated that UPA reduced expected pregnancy rates by approximately 62% compared to approximately 49% for LNG over 120 hours, with the advantage greatest when treatment was delayed beyond 72 hours. UPA requires a prescription in most countries, consistent with its approved indication for emergency contraception within a defined clinical window.9
A clinically critical pharmacological interaction exists between UPA and progestin-containing contraceptives. Because UPA is a PR modulator with partial antagonist activity at the PR, coadministration of progestin-containing contraceptives within 5 days after UPA use attenuates UPA efficacy by competing at the PR. Furthermore, UPA may reduce the efficacy of progestin-only contraceptives started in the days immediately following its use. Current UK Faculty of Sexual and Reproductive Healthcare (FSRH) guidance therefore recommends that hormonal contraception (combined or progestin-only) not be started for 5 days after UPA use, and that a barrier method be used during that interval. Conversely, women using continuous progestin-containing methods (combined oral contraceptive [COC], progestin-only pill [POP], implant, DMPA, LNG-IUD) at the time of UPA use should be counseled that UPA efficacy may be reduced, and the copper intrauterine device (IUD) should be recommended preferentially as EC in this context.10
The copper intrauterine device (IUD) is the most effective form of emergency contraception available, with a failure rate of less than 0.1% when inserted within 5 days of unprotected intercourse and providing ongoing contraception for up to 10 years. Its EC mechanism is mediated by the cytotoxic effects of copper ions on spermatozoa, which impair sperm motility and viability and prevent fertilization. Unlike pharmacological EC methods, the copper IUD is equally effective regardless of BMI, is not subject to drug interactions, is not dependent on pre-ovulatory timing, and can prevent pregnancy from intercourse up to 5 days prior to insertion (the maximum lifespan of sperm in the reproductive tract). The copper IUD is the preferred EC option for women with BMI above 35 kg/m², those currently using progestin-containing methods who need EC (where UPA efficacy is uncertain), those who require highly reliable ongoing contraception, and those in whom pharmacological EC failed or was contraindicated.6
Women currently using a COC, POP, implant, DMPA, or LNG-IUD who need emergency contraception face a pharmacological dilemma: UPA efficacy is attenuated by ambient progestin PR occupancy, and LNG EC adds further progestin, potentially increasing ongoing contraceptive failure. The pharmacologically sound recommendation is the copper IUD, which works by a completely different mechanism (copper ion sperm toxicity) that is unaffected by any hormonal method. If IUD insertion is not possible, UPA is still preferred over LNG EC in this scenario based on its greater post-LH-surge activity.
The drug interactions affecting hormonal contraceptive efficacy operate through two principal mechanisms: cytochrome P450 3A4 (CYP3A4) induction accelerating the hepatic and intestinal oxidative metabolism of ethinyl estradiol (EE) and most progestins, and uridine diphosphate glucuronosyltransferase (UGT) induction accelerating glucuronidation conjugation of EE, progestins, or co-administered drugs including lamotrigine. Because EE and progestins must maintain minimum plasma concentrations for both gonadotropin suppression and cervical mucus effects, even moderate reductions in plasma drug levels can shift an effective contraceptive regimen into a subtherapeutic range. The clinical consequence ranges from breakthrough ovulation (COCs containing induced EE and progestin) to mucus permeability recovery (progestin-only methods at induced plasma levels). Drug interactions with hormonal contraception therefore represent a patient safety issue, not merely a pharmacokinetic footnote.11
Rifampin remains the most clinically consequential CYP3A4 inducer affecting hormonal contraception. Rifampin induces CYP3A4 and cytochrome P450 2C9 (CYP2C9) via activation of the pregnane X receptor (PXR), a ligand-activated nuclear transcription factor that upregulates expression of multiple cytochrome P450 (CYP) enzymes and efflux transporters including P-glycoprotein (P-gp). The EE area under the concentration-time curve (AUC) is reduced by more than 50% with concurrent rifampin, and the levonorgestrel (LNG) AUC is reduced by approximately 40%. Enzymatic induction by rifampin persists for 4 to 6 weeks after the last rifampin dose because it takes that long for the newly induced enzyme protein to be cleared and pre-induction CYP3A4 expression to be restored. Rifabutin, a less potent PXR agonist used in Mycobacterium avium complex (MAC) prophylaxis, produces moderate but clinically meaningful CYP3A4 induction, and the WHO Medical Eligibility Criteria (MEC) recommends that all combined hormonal methods be classified as Category 3 with rifabutin use (risks generally outweigh advantages).1112
Among antiepileptic drugs (AEDs), enzyme-inducing agents that reduce combined and progestin-only oral contraceptive efficacy include carbamazepine, phenytoin, phenobarbital, primidone, oxcarbazepine, and topiramate at doses above 200 mg per day. These agents activate PXR and/or the constitutive androstane receptor (CAR), inducing hepatic CYP3A4, CYP2C9, and UGT enzymes. The WHO MEC classifies combined hormonal methods (COC, patch, ring) as Category 3 with enzyme-inducing AEDs, meaning the risks generally outweigh advantages because contraceptive failure rates approach those of no contraception in women on high-dose inducers. The levonorgestrel-intrauterine device (LNG-IUD) is Category 1 (no restriction) with enzyme-inducing AEDs because it acts locally at the endometrium and cervix at concentrations far exceeding plasma levels, and the depot medroxyprogesterone acetate (DMPA) is Category 2 (advantages outweigh risks) based on the large depot buffer against induction. The etonogestrel implant, despite being highly effective in non-drug-interacting contexts, is considered Category 2 with enzyme-inducing AEDs by some authorities and Category 3 by others, and Faculty of Sexual and Reproductive Healthcare (FSRH) guidance recommends against implant use in women on strong CYP3A4 inducers. Non-enzyme-inducing AEDs, including valproate, levetiracetam, lamotrigine, gabapentin, pregabalin, zonisamide, and lacosamide, do not reduce hormonal contraceptive efficacy through CYP3A4 induction, and any hormonal method can be used without additional contraceptive precautions on this pharmacokinetic basis.1112
The lamotrigine–EE interaction is the most clinically significant bidirectional drug interaction in contraceptive pharmacology. EE is a potent inducer of uridine diphosphate glucuronosyltransferase 1A4 (UGT1A4), the primary glucuronidation enzyme responsible for lamotrigine inactivation. When a woman stabilized on lamotrigine for epilepsy begins a combined hormonal method containing EE (COC, patch, or ring), EE-driven UGT1A4 induction accelerates lamotrigine glucuronidation and reduces lamotrigine plasma concentrations by 40 to 65% within 2 to 4 weeks of COC initiation, potentially precipitating breakthrough seizures in previously well-controlled epilepsy. The inverse occurs when the EE-containing method is discontinued: UGT1A4 activity falls back to baseline over 1 to 2 weeks and lamotrigine levels rebound sharply, creating a risk of lamotrigine toxicity manifesting as dizziness, diplopia, ataxia, or confusion. This same rebound occurs during the hormone-free interval of cyclic 21/7 combined pill regimens, where lamotrigine levels fluctuate cyclically in parallel with EE exposure. Because pure progestin-containing methods contain no EE, they do not induce UGT1A4 and do not affect lamotrigine levels; they are therefore the pharmacologically preferred hormonal contraceptive option in women stabilized on lamotrigine monotherapy, and the LNG-IUD or etonogestrel implant represent the ideal choices combining efficacy, safety, and freedom from lamotrigine interaction.12
Among antiretroviral drugs, the clinical significance of interactions with hormonal contraception varies substantially by drug class. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine are potent CYP3A4 inducers that reduce EE and progestin AUCs by 40 to 60%; the WHO MEC classifies COC use with efavirenz as Category 2 (acceptable with caution) and reinforces the use of barrier methods in addition to hormonal contraception. Rilpivirine (an NNRTI) and integrase strand-transfer inhibitors (INSTIs) including dolutegravir, raltegravir, elvitegravir, and bictegravir do not meaningfully alter EE or progestin pharmacokinetics and are the preferred antiretroviral agents in women prioritizing reliable hormonal contraception. Ritonavir-boosted protease inhibitors (PIs) present a complex interaction: ritonavir is a potent CYP3A4 inhibitor but paradoxically reduces EE AUC by 40 to 50% through induction of EE glucuronidation via UGT enzymes, requiring caution with all combined hormonal methods. Cobicistat, used as a pharmacokinetic booster in several fixed-dose antiretroviral combinations, similarly reduces EE exposure and renders combined hormonal methods unreliable.6
Enzyme-inducing AEDs (carbamazepine, phenytoin, phenobarbital, oxcarbazepine, topiramate above 200 mg/day): avoid oral, patch, and ring combined methods; LNG-IUD is Category 1 (use freely); DMPA is Category 2; implant is Category 2–3 depending on guidance used. Non-inducing AEDs (valproate, levetiracetam, lamotrigine, gabapentin, pregabalin): any hormonal method is pharmacokinetically acceptable, but specifically for lamotrigine: avoid EE-containing methods (UGT1A4 induction reduces lamotrigine levels); prefer progestin-only or non-hormonal methods to eliminate the bidirectional interaction risk.
The WHO Medical Eligibility Criteria for Contraceptive Use (WHO MEC) provides a four-category classification system grading the safety of contraceptive use in the presence of specific conditions. Category 1 designates no restriction; Category 2 indicates that advantages generally outweigh theoretical or proven risks; Category 3 indicates that theoretical or proven risks generally outweigh the advantages, meaning the method is not recommended unless other options are unavailable or unacceptable; and Category 4 is an absolute contraindication where the method represents an unacceptable health risk. The framework separates initiation from continuation, recognizing that a condition developing during ongoing use may require discontinuation of a previously appropriate method.6
The combined hormonal contraceptive methods (combined oral contraceptive [COC], combined patch, combined vaginal ring) share a common Category 4 contraindication profile driven largely by the estrogen component, particularly ethinyl estradiol (EE). Venous thromboembolism history or active deep vein thrombosis (DVT) or pulmonary embolism (PE) is a Category 4 absolute contraindication because EE-induced coagulation factor synthesis and reduced activated protein C (APC) sensitivity create an additive thrombotic risk with underlying thrombophilia or prior thrombotic events. Known thrombogenic mutations including factor V Leiden homozygosity, prothrombin gene mutation G20210A [prothrombin 20210A variant] homozygosity, protein C or S deficiency, and antithrombin III deficiency are Category 4 absolute contraindications for combined methods because the combined thrombotic risk may produce a 50-fold or higher elevation over baseline venous thromboembolism (VTE) risk. Migraine with aura is Category 4 for combined methods because EE is associated with a two-fold increase in ischemic stroke risk in women with migraine with aura, a risk that is multiplicative rather than additive when combined with the underlying aura-associated stroke risk.13613
Hypertension is graded by severity: adequately controlled hypertension is WHO MEC Category 3 for combined methods (not recommended but not absolutely contraindicated) because EE-driven hepatic angiotensinogen production raises blood pressure and amplifies cardiovascular risk; systolic blood pressure above 160 mmHg or diastolic above 100 mmHg is Category 4 for combined methods because the risk of stroke and myocardial infarction is unacceptably elevated. Smoking in women over age 35 is Category 3 for combined methods and Category 4 in women over 35 who smoke more than 15 cigarettes per day, reflecting the synergistic arterial thrombotic risk between EE-mediated platelet activation and smoking-induced endothelial injury. Valvular heart disease complicated by pulmonary arterial hypertension, atrial fibrillation, or a history of subacute bacterial endocarditis is Category 4 because EE-related VTE risk combines with the already elevated arterial and venous thrombotic risk of these cardiac lesions.6
Active liver disease, hepatocellular carcinoma, or hepatic adenoma is Category 4 for combined methods because EE is metabolized and extensively processed in the liver, and hepatic first-pass stimulation of an already compromised liver can worsen hepatic function or stimulate hepatic tumor growth. Breastfeeding women in the first 6 weeks postpartum are Category 4 for combined methods because neonatal exposure to exogenous estrogen through breast milk during the critical period of hepatic enzyme maturation in the neonate carries theoretical risk, and because early postpartum estrogen use increases VTE risk in an already hypercoagulable period. Known or suspected estrogen- or progestogen-sensitive malignancy, specifically current breast cancer, is Category 4 for all hormonal methods (combined and progestin-only alike) because exogenous hormone administration in the context of a hormone receptor-positive tumor carries an unacceptable risk of stimulating tumor growth or recurrence.6
Progestin-only methods carry a substantially narrower contraindication profile because they do not contain EE and do not produce the hepatic coagulation factor induction or endothelial effects associated with estrogen. The WHO MEC classifies progestin-only pills, the etonogestrel implant, and depot medroxyprogesterone acetate (DMPA) as Category 1 or 2 for most conditions that are Category 3 or 4 for combined methods, including prior VTE, thrombophilia, migraine with aura, hypertension (except very severe or with vascular disease), breastfeeding, and age over 35 with smoking. The levonorgestrel-intrauterine device (LNG-IUD) is similarly Category 2 for most conditions that are Category 3 or 4 for combined methods. The most important residual concern with progestin-only methods is current breast cancer, which remains Category 4 for all hormonal methods, and severe decompensated cirrhosis or hepatic tumors, which are Category 3 for implants and Category 3 or 4 for DMPA owing to possible hepatic metabolism concerns with systemic progestin exposure in severely compromised livers.6
Migraine with aura carries a two-fold baseline increase in ischemic stroke risk, likely related to cortical spreading depression and platelet activation during aura episodes. EE in combined methods additively increases this risk, making combined methods an absolute contraindication. Progestin-only methods do not carry this arterial risk amplification and are classified as Category 2 (safe with advantages outweighing risks). This distinction is clinically critical because migraine is common in women of reproductive age, and many clinicians incorrectly apply the combined method contraindication to all hormonal methods. The LNG-IUD or etonogestrel implant are the preferred hormonal options in this population.
Hatcher RA, Nelson AL, Trussell J, et al. Contraceptive Technology, 21st ed. Ayer Company Publishers; 2018. ISBN: 978-1-597080-02-6.
McCann MF, Potter LS. Progestin-only oral contraception: a comprehensive review. Contraception. 1994;50(6 Suppl 1):S1–195. PMID: 10226677.
Trussell J. Contraceptive failure in the United States. Contraception. 2011;83(5):397–404.
doi:10.1016/j.contraception.2011.01.021Schindler AE. Non-contraceptive benefits of oral hormonal contraceptives. Int J Endocrinol Metab. 2013;11(1):41–47.
doi:10.5812/ijem.4158Lidegaard O, Nielsen LH, Skovlund CW, Skjeldestad FE, Lokkegaard E. Risk of venous thromboembolism from use of oral contraceptives containing different progestogens and oestrogen doses. BMJ. 2011;343:d6423.
doi:10.1136/bmj.d6423World Health Organization. Medical Eligibility Criteria for Contraceptive Use, 5th ed. WHO Press; 2015. Available at: https://www.who.int/publications/i/item/9789241549158
Mansour D, Inki P, Gemzell-Danielsson K. Efficacy of contraceptive methods: a review of the literature. Eur J Contracept Reprod Health Care. 2010;15(1):4–16.
doi:10.3109/13625180903427675Nilsson CG, Haukkamaa M, Vierola H, Luukkainen T. Tissue concentrations of levonorgestrel in women using a levonorgestrel-releasing IUD. Clin Endocrinol (Oxf). 1982;17(5):529–536.
doi:10.1111/j.1365-2265.1982.tb01625.xGlasier AF, Cameron ST, Fine PM, et al. Ulipristal acetate versus levonorgestrel for emergency contraception: a randomised non-inferiority trial and meta-analysis. Lancet. 2010;375(9714):555–562.
doi:10.1016/S0140-6736(10)60101-8Brache V, Cochon L, Deniaud M, Croxatto HB. Ulipristal acetate prevents ovulation more effectively than levonorgestrel: analysis of pooled data from three randomized trials of emergency contraception regimens. Contraception. 2013;88(5):611–618.
doi:10.1016/j.contraception.2013.05.010Simmons KB, Haddad LB, Nanda K, Curtis KM. Drug interactions between rifamycin antibiotics and hormonal contraception: a systematic review. BJOG. 2018;125(7):804–811.
doi:10.1111/1471-0528.15027Reimers A, Brodtkorb E, Sabers A. Interactions between hormonal contraception and antiepileptic drugs: clinical and mechanistic considerations. Seizure. 2015;28:66–70.
doi:10.1016/j.seizure.2015.03.006Lidegaard O, Lokkegaard E, Jensen A, Skovlund CW, Keiding N. Thrombotic stroke and myocardial infarction with hormonal contraception. N Engl J Med. 2012;366(24):2257–2266.
doi:10.1056/NEJMoa1111840