Everything You Need to Know About Opioid use disorder (naloxone, methadone) for Step 1

Opioid questions on Step 1 are “free points” if you can (1) recognize intoxication vs withdrawal, (2) know naloxone cold, and (3) understand maintenance therapy (methadone vs buprenorphine vs naltrexone). This post is your high-yield, exam-ready deep dive—with the classic associations and the traps that love to show up on test day.

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What counts as an opioid?

Opioids include:

• Heroin
• Morphine
• Codeine
• Oxycodone, hydrocodone
• Fentanyl
• Methadone
• Loperamide (yes—peripheral opioid agonist; abuse can still cause issues)
• Buprenorphine (partial agonist; used for OUD)

First Aid cross-reference (Psychiatry—Substance Use Disorders): Opioid intoxication/withdrawal, methadone/buprenorphine/naltrexone, naloxone.

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Definition: Opioid Use Disorder (OUD)

OUD is a problematic pattern of opioid use leading to clinically significant impairment or distress.

DSM-5 pattern recognition (Step-style)

You’ll often see:

• Craving
• Tolerance
• Withdrawal
• Time spent obtaining/using/recovering
• Failure to fulfill obligations
• Continued use despite harm (medical, legal, social)

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High-yield nuance: DSM-5 criteria are not typically tested verbatim on Step 1, but tolerance/withdrawal + functional impairment often appear in vignettes.

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Pathophysiology (why opioids cause what they cause)

Opioids primarily act at $\mu$-opioid receptors (Gi-coupled):

• ↓ Adenylyl cyclase → ↓ cAMP
• ↓ Ca$^{2+}$ influx presynaptically → ↓ neurotransmitter release (e.g., substance P, glutamate)
• ↑ K$^+$ efflux postsynaptically → hyperpolarization

Key physiologic effects (tie these to symptoms)

• Analgesia (spinal cord + brain)
• Euphoria/sedation (reward pathways; disinhibition of dopamine)
• Respiratory depression (brainstem—medullary respiratory centers)
• Constipation (↓ GI motility)
• Miosis (parasympathetic outflow)

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HY mechanism: Opioids can increase dopamine in the nucleus accumbens by inhibiting GABAergic neurons that normally suppress dopamine release (disinhibition).

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Clinical presentation: Intoxication vs Withdrawal

Opioid intoxication (think: “down and pinpoint”)

Classic triad:

1. CNS depression
2. Respiratory depression
3. Miosis (pinpoint pupils)

Other common findings:

• Bradycardia, hypotension
• Decreased bowel sounds/constipation
• Track marks (IV use), abscesses, endocarditis risk
• Pulmonary edema (can occur in overdose)

Step trap: “Pinpoint pupils” isn’t always present

• Severe hypoxia can cause mydriasis later.
• Co-ingestions can muddy pupil findings.

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Opioid withdrawal (think: “up and miserable”)

Withdrawal is usually not life-threatening (unlike alcohol/benzos), but it is intensely uncomfortable.

Symptoms:

• Rhinorrhea, lacrimation
• Yawning
• Piloerection (“cold turkey”), chills
• Myalgias
• Diarrhea, abdominal cramping
• Nausea/vomiting
• Mydriasis
• Tachycardia, hypertension
• Anxiety, irritability

Mnemonic vibe: “Dilated pupils + diarrhea + dysphoria.”

Timing (high-yield)

• Short-acting opioids (heroin): withdrawal begins ~6–12 hours
• Long-acting (methadone): withdrawal begins ~24–48 hours, lasts longer

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Diagnosis: How it shows up in vignettes

Overdose diagnosis is clinical

If the stem screams opioid overdose (somnolence + slow breathing ± pinpoint pupils), treat immediately—don’t wait.

Likely clues:

• RR is low (e.g., 6/min), patient difficult to arouse
• Needle nearby / pill bottles / fentanyl patches
• Cyanosis

Labs you might see (Step 1 logic)

• ABG: respiratory acidosis (hypoventilation)
• Urine drug screen: may miss synthetic opioids (e.g., fentanyl) depending on assay

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Treatment: The Step 1 must-knows

1) Acute opioid overdose: Naloxone

Naloxone = opioid receptor antagonist (competitive; highest yield at $\mu$ receptors)

When to give it

• Suspected opioid toxicity with respiratory depression or significant CNS depression

What happens after naloxone?

• Rapid reversal of respiratory/CNS depression
• Can precipitate acute withdrawal in dependent patients (agitation, vomiting, tachycardia)

HY pitfall: Duration mismatch

Naloxone has a short half-life, so recurrent respiratory depression can occur—especially with long-acting opioids (methadone, extended-release oxycodone) or potent fentanyl analogs.

Practical implication tested on boards:

• Monitor and redose or infusion if needed.

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2) Long-term management of OUD (maintenance + harm reduction)

Medication for opioid use disorder (MOUD) saves lives

Expect Step questions asking which med decreases mortality/relapse.

Core options

• Methadone (full $\mu$ agonist)
• Buprenorphine (partial $\mu$ agonist; $\kappa$ antagonist)
• Naltrexone (opioid antagonist; for relapse prevention after detox)

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Methadone (high-yield deep dive)

What it is: Full $\mu$-opioid receptor agonist used for maintenance therapy and chronic pain.

Why it works for OUD:

• Long-acting → prevents withdrawal
• Reduces cravings
• Blunts euphoric effects of other opioids via receptor occupancy

Where it’s given (classic board point):

• Often through specialized opioid treatment programs (more regulated than buprenorphine)

Major adverse effects (memorize)

• Respiratory depression (especially when starting or mixing sedatives)
• QT prolongation → torsades de pointes
• Constipation, sedation

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HY association: Methadone + QT prolongation is a recurring Step fact. If you see syncope + prolonged QT on ECG in a patient on methadone, think torsades risk.

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Buprenorphine (quick contrast)

Partial agonist at $\mu$ receptor → has a ceiling effect on respiratory depression.

Why Step loves it:

• Safer in overdose than full agonists
• Can be prescribed in office-based settings (less restrictive than methadone in many contexts)

Pearl: If started too soon after full agonist use, buprenorphine can precipitate withdrawal (it displaces full agonists but provides less agonism).

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Naltrexone (where it fits)

Opioid receptor antagonist used for relapse prevention.

High-yield rule:

• Must be opioid-free before starting (otherwise precipitated withdrawal)

Also used for alcohol use disorder (boards like cross-linking).

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Quick comparison table (Step-friendly)

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High-yield associations & classic Step stems

1) Overdose vignette

Stem: Somnolent, RR 6/min, pinpoint pupils, needle nearby
Answer: Naloxone (and airway/ventilation support)

2) “He wants to quit heroin and avoid withdrawal”

Best long-term: MOUD (methadone or buprenorphine)
Not just “detox and counseling” as sole therapy (relapse risk high)

3) Methadone adverse effect

Stem: On methadone maintenance, episodes of syncope; ECG shows prolonged QT
Answer: Torsades risk (QT prolongation)

4) Withdrawal vs intoxication pupil clue

• Intoxication: miosis
• Withdrawal: mydriasis

5) Opioids and constipation

Stem: Chronic opioid use + abdominal distention, no bowel movement
Concept: Opioids decrease gut motility (often treated clinically with stimulant laxatives/peripherally acting antagonists—Step more often tests the association than the specific drug)

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First Aid-style rapid review (what to memorize)

• Opioid intoxication: CNS depression + respiratory depression + miosis
• Opioid withdrawal: mydriasis, lacrimation/rhinorrhea, yawning, piloerection, diarrhea, cramps, aches
• Naloxone: acute reversal; short duration
• Methadone: maintenance; QT prolongation
• Buprenorphine: partial agonist; ceiling effect; can precipitate withdrawal
• Naltrexone: antagonist for relapse prevention; must detox first

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Mini self-check (1-minute)

1. Patient overdosed on heroin, improved after naloxone, then worsens again 45 minutes later. Why?
   Naloxone wears off before the opioid—needs repeat dosing/infusion and monitoring.

2. Which maintenance med is associated with QT prolongation?
   Methadone.

3. Withdrawal pupil size?
   Dilated (mydriasis).