Drug Classification · Questions 1–6
Identify the pharmacological class or categorical label for each drug or receptor. Vocabulary preparation is sufficient to answer every question in this section.
Question 1 · Drug Classification
Which of the following antidepressant drug classes includes fluoxetine as one of its members?
Correct Answer
B — Selective serotonin reuptake inhibitors
Rationale
Fluoxetine belongs to the selective serotonin reuptake inhibitor class of antidepressants. The selective serotonin reuptake inhibitors are the most widely prescribed antidepressant class and include six agents: fluoxetine, sertraline, paroxetine, citalopram, escitalopram, and fluvoxamine. Tricyclic antidepressants include agents such as amitriptyline and nortriptyline. Serotonin-norepinephrine reuptake inhibitors include venlafaxine and duloxetine. Monoamine oxidase inhibitors include phenelzine and tranylcypromine.
Question 2 · Drug Classification
Phenelzine is classified as a member of which of the following antidepressant drug classes?
Correct Answer
A — Monoamine oxidase inhibitors
Rationale
Phenelzine is a monoamine oxidase inhibitor, one of the oldest antidepressant drug classes. Other monoamine oxidase inhibitors include tranylcypromine and the reversible agent moclobemide. Selective serotonin reuptake inhibitors include fluoxetine, sertraline, and paroxetine. Serotonin-norepinephrine reuptake inhibitors include venlafaxine and duloxetine. Tricyclic antidepressants include amitriptyline and nortriptyline.
Question 3 · Drug Classification
Amitriptyline is classified as a member of which of the following antidepressant drug classes?
Correct Answer
C — Tricyclic antidepressants
Rationale
Amitriptyline is a tricyclic antidepressant, named for the three-ring chemical structure shared by agents in this class. Other tricyclic antidepressants include nortriptyline, imipramine, desipramine, clomipramine, and doxepin. Selective serotonin reuptake inhibitors include fluoxetine and sertraline. Monoamine oxidase inhibitors include phenelzine and tranylcypromine. Norepinephrine-dopamine reuptake inhibitors is the class to which bupropion belongs.
Question 4 · Drug Classification
Bupropion is classified as a member of which of the following antidepressant drug classes?
Correct Answer
D — Norepinephrine-dopamine reuptake inhibitors
Rationale
Bupropion is classified as a norepinephrine-dopamine reuptake inhibitor, making it pharmacologically distinct from all other antidepressant classes. It is the only widely used antidepressant that primarily targets the norepinephrine and dopamine transporters without meaningful serotonin transporter activity. Tricyclic antidepressants include amitriptyline and nortriptyline. Selective serotonin reuptake inhibitors include fluoxetine and sertraline. Serotonin-norepinephrine reuptake inhibitors include venlafaxine and duloxetine.
Question 5 · Drug Classification
Venlafaxine is classified as a member of which of the following antidepressant drug classes?
Correct Answer
B — Serotonin-norepinephrine reuptake inhibitors
Rationale
Venlafaxine is a serotonin-norepinephrine reuptake inhibitor, a class that also includes duloxetine, desvenlafaxine, and levomilnacipran. Serotonin-norepinephrine reuptake inhibitors are distinguished from selective serotonin reuptake inhibitors by their additional blockade of the norepinephrine transporter. Monoamine oxidase inhibitors include phenelzine and tranylcypromine. Selective serotonin reuptake inhibitors include fluoxetine and sertraline. Tricyclic antidepressants include amitriptyline and nortriptyline.
Question 6 · Drug Classification
Which of the following drugs is NOT classified as a selective serotonin reuptake inhibitor?
Correct Answer
C — Venlafaxine
Rationale
Venlafaxine is a serotonin-norepinephrine reuptake inhibitor, not a selective serotonin reuptake inhibitor. The six selective serotonin reuptake inhibitors are fluoxetine, sertraline, paroxetine, citalopram, escitalopram, and fluvoxamine. Sertraline, fluoxetine, and paroxetine all belong to the selective serotonin reuptake inhibitor class. Venlafaxine is distinguished by its additional blockade of the norepinephrine transporter, placing it in a separate drug class.
Core Pharmacology · Questions 7–14
Apply your understanding of drug mechanisms, pharmacokinetics, and adverse effects. Each question requires one reasoning step.
Question 7 · Core Pharmacology
The monoamine hypothesis proposes that major depressive disorder results from a functional deficiency of one or more monoamine neurotransmitters. Which of the following neurotransmitters are the principal targets of this hypothesis?
Correct Answer
A — Serotonin, norepinephrine, and dopamine
Rationale
The monoamine hypothesis of depression identifies functional deficiency of three principal monoamine neurotransmitters: serotonin, norepinephrine, and dopamine. Serotonin, projecting from the dorsal raphe nucleus, regulates mood, anxiety, sleep, and appetite. Norepinephrine, projecting from the locus coeruleus, modulates attention, arousal, and the stress response. Dopamine, acting through mesolimbic and mesocortical pathways, governs motivation and reward and underlies the anhedonia of severe depression. Acetylcholine, histamine, glutamate, gamma-aminobutyric acid, and glycine are neurotransmitters associated with other pharmacological systems; the monoamine hypothesis centers specifically on serotonin, norepinephrine, and dopamine.
Question 8 · Core Pharmacology
A selective serotonin reuptake inhibitor begins blocking the serotonin reuptake transporter within hours of the first dose, yet patients typically require two to four weeks of continuous treatment before experiencing meaningful antidepressant benefit. Which of the following best explains this delay?
Correct Answer
C — Presynaptic autoreceptors initially limit serotonin release and must desensitize before full therapeutic benefit occurs
Rationale
When a selective serotonin reuptake inhibitor first blocks the serotonin reuptake transporter, synaptic serotonin levels rise acutely. This rise activates presynaptic autoreceptors, which respond by reducing serotonin synthesis and release — a negative feedback response that partially counteracts the drug's effect. With continuous treatment over two to four weeks, these autoreceptors gradually desensitize and lose their inhibitory responsiveness. Once desensitized, serotonin release is no longer suppressed, allowing the full synaptic serotonin elevation to develop and produce antidepressant benefit. Selective serotonin reuptake inhibitors reach steady-state plasma concentrations within days, ruling out the accumulation explanation. Postsynaptic receptor downregulation does occur over time but is a consequence of treatment, not the explanation for the delay in therapeutic onset.
Question 9 · Core Pharmacology
Selective serotonin reuptake inhibitors are described as "selective" because at standard therapeutic doses they show strong preference for one monoamine reuptake transporter over the others. Which transporter is the primary target of this drug class?
Correct Answer
B — The serotonin reuptake transporter
Rationale
Selective serotonin reuptake inhibitors are far more potent at blocking the serotonin reuptake transporter than at blocking the norepinephrine or dopamine transporters at standard therapeutic doses. This selectivity is why their primary clinical effects and adverse effects are serotonin-mediated. Selectivity is relative, not absolute — paroxetine, for example, has meaningful anticholinergic activity at therapeutic doses — but the serotonin reuptake transporter remains the defining pharmacological target of the class. Dual inhibition of both the serotonin reuptake transporter and the norepinephrine transporter at comparable potency defines the serotonin-norepinephrine reuptake inhibitor class, not the selective serotonin reuptake inhibitor class.
Question 10 · Core Pharmacology
Bupropion blocks the norepinephrine and dopamine transporters but has no meaningful activity at the serotonin reuptake transporter. Based on this mechanism, which of the following adverse effects would be least expected with bupropion compared to selective serotonin reuptake inhibitors?
Correct Answer
D — Sexual dysfunction and nausea
Rationale
Sexual dysfunction and nausea are the two most clinically prominent serotonin-mediated adverse effects of selective serotonin reuptake inhibitors. Because bupropion has no activity at the serotonin reuptake transporter, it does not produce these serotonergic adverse effects — a property that makes it a common augmentation choice for patients who develop sexual dysfunction on a selective serotonin reuptake inhibitor. Insomnia, agitation, headache, and dry mouth can occur with bupropion through its dopaminergic and noradrenergic activity and are not serotonin-specific. Seizure risk at high doses is a bupropion-specific adverse effect related to its dopaminergic and noradrenergic activity and is present with bupropion but absent with selective serotonin reuptake inhibitors.
Question 11 · Core Pharmacology
Both selective serotonin reuptake inhibitors and monoamine oxidase inhibitors increase synaptic monoamine availability, but they do so through entirely different mechanisms. Which of the following best describes how monoamine oxidase inhibitors achieve this effect?
Correct Answer
A — They inhibit the enzyme responsible for breaking down monoamines in the presynaptic neuron and synaptic cleft
Rationale
Monoamine oxidase is the principal enzyme responsible for degrading serotonin, norepinephrine, and dopamine within presynaptic neurons and at the synapse. Monoamine oxidase inhibitors block this enzymatic breakdown, causing monoamines to accumulate to higher concentrations — the same pharmacological goal as reuptake inhibition, achieved by an entirely different mechanism. Blocking the serotonin reuptake transporter describes the mechanism of selective serotonin reuptake inhibitors. Stimulating monoamine synthesis describes a mechanism that no approved antidepressant class uses as its primary action. Blocking the norepinephrine and dopamine transporters without affecting serotonin describes the mechanism of bupropion, a norepinephrine-dopamine reuptake inhibitor.
Question 12 · Core Pharmacology
Selective serotonin reuptake inhibitors are approved for a broad range of conditions beyond major depressive disorder. Which of the following conditions represents an approved indication for this drug class?
Correct Answer
C — Generalized anxiety disorder
Rationale
Selective serotonin reuptake inhibitors are first-line pharmacotherapy for generalized anxiety disorder, as well as for panic disorder, social anxiety disorder, post-traumatic stress disorder, and obsessive-compulsive disorder. The serotonergic mechanism that underlies their antidepressant effect also mediates anxiolytic activity, which accounts for their broad utility across both mood and anxiety conditions. Bipolar disorder requires mood stabilizers; selective serotonin reuptake inhibitors are used cautiously in bipolar disorder and are not approved as monotherapy because they can precipitate mania. Schizophrenia is treated with antipsychotic agents. Attention deficit hyperactivity disorder is treated primarily with stimulants and norepinephrine-targeted agents such as atomoxetine, not with selective serotonin reuptake inhibitors.
Question 13 · Core Pharmacology
Fluoxetine is administered orally, but a portion of the absorbed drug is metabolized by the liver before reaching the systemic circulation. Which pharmacokinetic term describes this process, and what is its primary consequence?
Correct Answer
B — First-pass metabolism — reduces the fraction of the dose that reaches systemic circulation
Rationale
First-pass metabolism refers to the hepatic metabolism of a drug that occurs between oral absorption from the gut and entry into the systemic circulation. Because the portal circulation delivers absorbed drug directly to the liver before it reaches other tissues, a drug that is extensively metabolized by the liver will have a reduced oral bioavailability — meaning the fraction of the administered dose that reaches systemic circulation is less than 100 percent. Fluoxetine undergoes first-pass metabolism, contributing to its effective bioavailability after oral dosing. Enterohepatic recirculation involves drugs that are secreted into bile and reabsorbed from the intestine — a process that can prolong drug exposure, but is not the term for hepatic extraction before systemic distribution. Renal clearance removes drug from plasma after systemic distribution. Volume of distribution describes how a drug partitions between plasma and tissues once in systemic circulation.
Question 14 · Core Pharmacology
Tricyclic antidepressants produce their antidepressant effect through blockade of monoamine reuptake transporters. Which of the following correctly describes which transporters tricyclic antidepressants inhibit?
Correct Answer
D — Both the serotonin reuptake transporter and the norepinephrine transporter, producing dual monoaminergic enhancement
Rationale
Tricyclic antidepressants inhibit both the serotonin reuptake transporter and the norepinephrine transporter, producing dual monoaminergic enhancement analogous to the serotonin-norepinephrine reuptake inhibitor class. This dual mechanism underlies their antidepressant efficacy and their particular usefulness in depression accompanied by pain, fatigue, or prominent noradrenergic symptoms. The critical pharmacological distinction between tricyclic antidepressants and modern serotonin-norepinephrine reuptake inhibitors lies in off-target receptor binding rather than reuptake mechanism — tricyclic antidepressants also block muscarinic, histamine H1, and alpha-1 adrenergic receptors at therapeutic doses, producing substantial adverse effects. Selective serotonin reuptake inhibitors, not tricyclic antidepressants, preferentially target the serotonin reuptake transporter alone. Dopamine transporter blockade as a primary mechanism describes bupropion.
Clinical Correlations · Questions 15–18
Apply pharmacological knowledge to clinical scenarios. Each vignette presents a patient situation; the question tests mechanism of action or drug selection.
Question 15 · Clinical Correlations
A 34-year-old woman is started on a selective serotonin reuptake inhibitor for major depressive disorder. One week later she calls to report that she feels no better and asks whether the medication is working. Her physician explains that the drug is acting at the serotonin reuptake transporter immediately but that clinical improvement typically requires two to four weeks. Which of the following best explains why antidepressant benefit is delayed despite immediate transporter blockade?
Correct Answer
C — Presynaptic autoreceptors initially suppress serotonin release in response to rising synaptic serotonin levels and must desensitize over weeks before full serotonergic tone develops
Rationale
When a selective serotonin reuptake inhibitor begins blocking the serotonin reuptake transporter, synaptic serotonin rises acutely. Presynaptic autoreceptors detect this rise and respond by reducing serotonin synthesis and release — a compensatory feedback mechanism that limits the net serotonergic gain. With two to four weeks of continuous treatment, these autoreceptors desensitize and their inhibitory response diminishes. The full increase in synaptic serotonin can then develop, producing the antidepressant effect. This autoreceptor desensitization timeline corresponds to the observed delay in clinical benefit across all monoaminergic antidepressant classes. Selective serotonin reuptake inhibitors reach steady-state plasma concentrations within days, not weeks. Postsynaptic receptor upregulation and neuronal growth do not account for the clinical onset timeline.
Question 16 · Clinical Correlations
A 28-year-old man presents to his primary care physician with a six-week history of low mood, anhedonia, poor sleep, and difficulty concentrating. He also reports persistent worry and restlessness that has been present for over a year. His physician diagnoses him with both major depressive disorder and generalized anxiety disorder and decides to start a single pharmacological agent that is first-line for both conditions based on its mechanism of action. Which of the following drug classes is most appropriate?
Correct Answer
A — Selective serotonin reuptake inhibitors
Rationale
Selective serotonin reuptake inhibitors are first-line pharmacotherapy for both major depressive disorder and generalized anxiety disorder, making them the appropriate single-agent choice when both conditions are present. The serotonergic mechanism that produces antidepressant effects — increased synaptic serotonin through transporter blockade — also mediates anxiolytic activity in limbic circuits, accounting for the class's approved indications across both mood and anxiety disorders. Monoamine oxidase inhibitors are effective antidepressants but carry dietary restrictions and drug interaction risks that limit their use as first-line agents. Tricyclic antidepressants are effective but are avoided as first-line therapy due to their off-target receptor adverse effects and overdose lethality. Norepinephrine-dopamine reuptake inhibitors such as bupropion are approved for major depressive disorder but are not first-line agents for generalized anxiety disorder.
Question 17 · Clinical Correlations
A 41-year-old woman with major depressive disorder has had a partial response to a selective serotonin reuptake inhibitor but reports persistent fatigue and anhedonia, along with sexual dysfunction she attributes to the antidepressant. Her physician adds bupropion to her regimen, explaining that it works through a mechanism different from the selective serotonin reuptake inhibitor and is unlikely to worsen her sexual dysfunction. Which of the following best describes the mechanism of action of bupropion?
Correct Answer
D — Blockade of the norepinephrine and dopamine transporters without meaningful activity at the serotonin reuptake transporter
Rationale
Bupropion is a norepinephrine-dopamine reuptake inhibitor. It blocks the norepinephrine and dopamine transporters but has no meaningful activity at the serotonin reuptake transporter. Because sexual dysfunction and nausea are serotonin-mediated adverse effects, bupropion does not produce them — making it a useful addition for patients experiencing these adverse effects on a selective serotonin reuptake inhibitor. The dopaminergic activity also addresses fatigue and anhedonia, symptoms that reflect dopamine pathway involvement. Monoamine oxidase inhibition describes the mechanism of phenelzine and tranylcypromine. Equal potency at the serotonin reuptake transporter and norepinephrine transporter describes the serotonin-norepinephrine reuptake inhibitor class. Alpha-2 receptor antagonism describes the mechanism of mirtazapine.
Question 18 · Clinical Correlations
A 58-year-old man with hypertension is started on reserpine and returns four weeks later reporting low mood, loss of interest in activities he previously enjoyed, and persistent fatigue. His physician recognizes this as a drug-induced depressive syndrome and discontinues the medication. Which of the following best explains the mechanism by which reserpine produced these symptoms?
Correct Answer
B — Reserpine depletes vesicular stores of serotonin, norepinephrine, and dopamine, producing a functional monoamine deficiency at synapses
Rationale
Reserpine blocks the vesicular monoamine transporter, which is responsible for packaging serotonin, norepinephrine, and dopamine into synaptic vesicles for release. Without vesicular storage, monoamines accumulate in the cytoplasm and are degraded by monoamine oxidase. The result is a profound depletion of releasable monoamine stores, producing a functional deficiency at serotonergic, noradrenergic, and dopaminergic synapses. This monoamine depletion manifests clinically as a depressive syndrome, and it provided one of the earliest lines of evidence supporting the monoamine hypothesis of depression. Reserpine does not block postsynaptic receptors, inhibit monoamine oxidase, or interfere with the serotonin reuptake transporter — each of those mechanisms produces distinct pharmacological effects.