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Opioid use disorder matters because overdose and withdrawal look almost opposite to each other, and telling them apart quickly can be life-saving. It is diagnosed as a problematic pattern of opioid use causing significant impairment, with toleranceNeeding a larger dose of a drug over time to get the same effect.Read more →, craving, and continued use despite harm. For example, imagine a patient found unresponsive with pinpoint pupils and slow, shallow breathing after opioid use: this picture is an emergency requiring immediate reversal. In practice, recognising this specific pupil and breathing pattern instantly should trigger naloxone (an opioid antagonistA drug that blocks a receptor, stopping it from being activated.Read more → that reverses overdose) administration.

Overdose (intoxication) causes pinpoint (constricted) pupils, respiratory depression, and reduced consciousness, and is treated urgently with naloxone, an opioid antagonistA drug that blocks a receptor, stopping it from being activated.Read more → that displaces opioids from their receptors. Withdrawal, by contrast, is markedly different: dilated pupils, watery eyes, yawning, muscle aches, diarrhoea, and intense craving, all deeply unpleasant but not typically life-threatening. Picture a dependent patient forty-eight hours after their last dose, with dilated pupils, cramping, and diarrhoea, actively asking for more opioids: this is withdrawal, not overdose, and needs symptomatic treatment or opioid substitution rather than naloxone. In practice, mixing up overdose and withdrawal would mean giving naloxone to a patient in withdrawal, which offers no benefit and would worsen symptoms.

• A man is given buprenorphine two hours after his last heroin dose and rapidly becomes acutely unwell with withdrawal. Why did this happen?
• After naloxone reverses an opioid overdose, why must the patient stay under observation?
• During which period is the risk of death highest for a patient newly started on methadone maintenance?

• Opioid overdose, pinpoint pupils and life-threatening respiratory depression, unlike opioid withdrawal's dilated pupils and non-fatal course.
• Opioid withdrawal, intensely unpleasant but not typically fatal, whereas overdose can cause death from respiratory depression without prompt naloxone.
• Alcohol withdrawal, can cause seizures and delirium tremens, unlike opioid withdrawal, which causes severe discomfort but rarely seizures or delirium.
• Stimulant intoxication, causes dilated pupils and agitation from a different mechanism, rather than the sedation and pinpoint pupils of opioid overdose.

• A pure antagonistA drug that blocks a receptor, stopping it from being activated.Read more → describes naloxone or naltrexone, whereas buprenorphine retains partial agonistA drug that activates a receptor but produces a smaller effect than a full agonist, even at a high dose.Read more → activity.
• Buprenorphine does not raise heroin blood levels.
• Delayed seizures are not a recognised effect of naloxone.
• Naloxone has no significant effect on blood glucose.
• Gastrointestinal bleeding is not a naloxone effect.

• Extract the defining phenomenology, duration, severity and functional-impact clues.
• Match the pattern to the most specific diagnostic or assessment construct.
• Actively test the closest look-alike against the missing or contradictory clue.
• Choose the precise term rather than a broader category that is merely compatible.