You’ve seen it in UWorld/AMBOSS: a teen or young adult comes in “acting weird,” the stem mentions red eyes and snacks, and the question asks what drug or complication fits best. Cannabis questions look straightforward—but the real points come from knowing what cannabis does, what it doesn’t do, and how to separate it from common distractors (alcohol, stimulants, hallucinogens, opioids, PCP). Let’s break down a classic vignette and make every answer choice teach you something.
Tag: Psychiatry > Substance Use & Development
The Clinical Vignette (Q-bank style)
A 17-year-old boy is brought to clinic by his mother because his grades have dropped over the last semester. She says he has become “unmotivated” and spends most evenings in his room. He denies alcohol use. On exam, he is relaxed with conjunctival injection and a faint odor on his clothes. He reports that music sounds “more vivid” and that he eats a lot at night. Vitals are normal.
Which of the following additional findings is most likely?
A. Vertical nystagmus and severe hypertension
B. Dilated pupils, diaphoresis, and jaw clenching
C. Depressed respiratory rate and pinpoint pupils
D. Short-term memory impairment and slowed reaction time
E. Visual hallucinations with flashbacks months later
Correct Answer: D. Short-term memory impairment and slowed reaction time
Why cannabis fits the stem
This stem is packed with classic cannabis clues:
- Conjunctival injection (red eyes)
- Increased appetite (“munchies”)
- Altered perception (music “more vivid”)
- Amotivation / academic decline (especially in adolescents with heavy use)
- Often (but not always): tachycardia, dry mouth, impaired coordination
High-yield cannabis effects (Step-friendly list)
Acute intoxication
- Euphoria, relaxation
- Perceptual changes (time slows, heightened sensory perception)
- Impaired attention, concentration, and short-term memory
- Impaired coordination → increased risk of motor vehicle accidents
- Physical: conjunctival injection, tachycardia, increased appetite, dry mouth
Withdrawal (tested more than you’d think)
- Irritability, anxiety, insomnia
- Decreased appetite
- Restlessness, depressed mood
- Symptoms begin within ~1 day, peak in a few days, can last 1–2 weeks
Long-term/heavy use (esp. adolescents)
- Problems with learning and memory
- Poor academic/work performance
- Cannabis-induced anxiety or psychosis in vulnerable patients (risk increases with potency/frequency)
Mechanism
- THC acts on CB1 receptors (Gi-coupled) in CNS → alters neurotransmitter release (e.g., GABA/glutamate modulation)
“Why Every Answer Choice Matters”: Systematic Distractor Autopsy
A. Vertical nystagmus and severe hypertension → PCP (phencyclidine), not cannabis
This option screams PCP intoxication, a classic USMLE favorite.
PCP key findings
- Vertical or horizontal nystagmus (high yield)
- Hypertension, tachycardia
- Agitation, combativeness, psychosis
- Analgesia + “superhuman strength”
- Can cause severe violence and rhabdomyolysis
Cannabis doesn’t cause: vertical nystagmus or severe sympathetic instability as a hallmark.
B. Dilated pupils, diaphoresis, and jaw clenching → MDMA / amphetamines, not cannabis
This is the “rave stimulant” toxidrome.
MDMA/amphetamine features
- Mydriasis, diaphoresis, tachycardia, hypertension
- Bruxism/jaw clenching
- Euphoria + increased energy
- Dangerous complications: hyperthermia, serotonin syndrome (esp. MDMA), hyponatremia (MDMA)
Cannabis can cause: mild tachycardia, but not the classic stimulant triad of mydriasis + diaphoresis + bruxism.
C. Depressed respiratory rate and pinpoint pupils → Opioid intoxication, not cannabis
If you see miosis + respiratory depression, think opioids until proven otherwise.
Opioid intoxication triad
- CNS depression
- Respiratory depression
- Miosis
Management note: naloxone for overdose.
Cannabis does not typically cause clinically significant respiratory depression (important differentiator on exams).
D. Short-term memory impairment and slowed reaction time → Cannabis (correct)
This is the most Step-relevant cognitive effect of cannabis and explains real-world harm (driving, school, work).
Clinchers
- Conjunctival injection + increased appetite + perceptual changes + memory/attention impairment
E. Visual hallucinations with flashbacks months later → Hallucinogens (LSD) and hallucinogen persisting perception disorder (HPPD), not cannabis
“Flashbacks months later” is a hallmark association with LSD-class hallucinogens.
LSD intoxication
- Visual hallucinations, synesthesia
- Panic, paranoia
- Autonomic signs: mydriasis, tachycardia, hypertension
- Generally no severe respiratory depression
HPPD
- Re-experiencing perceptual symptoms after stopping hallucinogens
Cannabis can alter perception, but true formed visual hallucinations + flashbacks is far more consistent with hallucinogens.
Rapid Toxidrome Table (USMLE speed)
| Substance | Pupils | Key physical signs | Key psych/behavior | High-yield distinguishing clue |
|---|---|---|---|---|
| Cannabis | Normal or mild mydriasis | Conjunctival injection, ↑ appetite, tachycardia | Euphoria, relaxation, impaired short-term memory | “Red eyes + munchies + slowed reaction time” |
| PCP | Often normal | Vertical nystagmus, HTN, analgesia | Agitation, violence, psychosis | Nystagmus + “superhuman strength” |
| MDMA/amphetamines | Mydriasis | Diaphoresis, hyperthermia | Euphoria, energy, agitation | Bruxism + hyperthermia risk |
| Opioids | Miosis | Respiratory depression | Sedation | Triad: coma + miosis + resp depression |
| LSD | Mydriasis | Autonomic activation | Visual hallucinations | Flashbacks/HPPD |
Development Angle: Why Adolescents Are a Favorite Test Population
NBME-style questions love cannabis in teens because developmentally they’re vulnerable to:
- Academic and motivational decline (functional impairment)
- Cognitive effects (learning, attention, memory)
- Higher risk of cannabis use disorder with early initiation
- Increased likelihood of psychiatric comorbidity (anxiety; psychosis risk in predisposed individuals)
If the stem mentions:
- “Grades slipping,” “no longer plays sports,” “always in his room,” “new friend group,” or poor school attendance …think substance use + screen for cannabis, alcohol, nicotine/vaping, and depression.
Exam-Day Takeaways (what to memorize)
- Cannabis intoxication: conjunctival injection + ↑ appetite + impaired short-term memory/coordination
- Cannabis withdrawal: irritability, insomnia, decreased appetite, anxiety
- Distinguish from:
- PCP: vertical nystagmus, violent agitation
- Stimulants/MDMA: mydriasis + diaphoresis + hyperthermia/bruxism
- Opioids: miosis + respiratory depression
- LSD: hallucinations + flashbacks (HPPD)
When you review questions, don’t just learn the right drug—learn the “signature feature” that rules in the correct choice and rules out the distractors. That’s how you turn one cannabis question into five toxidromes you’ll never mix up again.