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Withdrawal: A syndrome of drug-specific symptoms, usually characterised by rebound effects in the same physiological systems initially altered by the drug, which occur when the drug is withdrawn partially or totally, not increased to overcome the effects of tolerance, or counteracted by a specific antagonist.

While all psychoactive drugs can produce psychological dependence, only those with a direct effect on neuronal receptors produce physical dependence and the potential for a withdrawal syndrome.

All misused psychoactive substances produce pleasure or euphoria

All withdrawal syndromes are unpleasant or dysphoric and most are associated with marked lability of mood.

Alcohol, benzodiazepines and other central nervous system (CNS) depressants produce a sense of relaxed calmness, decreased alertness, hyporeflexia, reduced muscle tone, loss of motor control, somnolence. All have anticonvulsant effects.

Withdrawal presents as psychomotor agitation, hypervigilance, tremors, diaphoresis, muscle tension and hyperreflexia, insomnia and disturbed sleep -- often with vivid dreams or nightmares. Withdrawal seizures and delirium tremens (in alcohol withdrawal) may occur.

Benzodiazepine withdrawal
Time to onset: one to five days
Average duration: two to six weeks

Alcohol withdrawal
Time to onset: 12-48 hours
Average duration: 2-10 days

Opioids (heroin, methadone, morphine, pethidine) produce a sense of calmness, drowsiness, flushing of skin, miosis, decreased respiratory rate and depth, drying of mucosa, analgesia.

Withdrawal manifests as psychomotor agitation, hot-and-cold flushes with piloerection, mydriasis, tachypnoea with yawning, diaphoresis, lacrimation, rhinorrhoea, muscle twitching or spasms, aching muscles, bones and joints.
Time to onset, duration and severity of withdrawal syndrome depends on which opioid has been used. Short-acting opioids, such as morphine, pethidine and heroin, have onsets within 4-6 hours of last dose and syndromes lasting 5-10 days. Long-acting opioids, such as methadone, have onsets of about 2-2.5 days and can last for up to 3-4 weeks.

CNS stimulants (amphetamine, cocaine) produce increased alertness, confidence, energy and sociability, loquacity, mydriasis, restlessness, sleeplessness, anorexia.

Withdrawal presents as lethargy, anergia, loss of confidence, social withdrawal, miosis, generalised fatigue and somnolence and increased appetite. Delusions or paranoid ideation may occur.
Time to onset: 4-8 hours
Average duration: 2-7 days

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