Acute and chronic effects, including overdose, from the use of - opioids

Description

Opioids (heroin, prescription opioids, fentanyl analogues, methadone, buprenorphine)
Acute: see toxidromes-opioid for the overdose picture
Chronic: tolerance, dependence, constipation, androgen deficiency (hypogonadism), immunosuppression, opioid-induced hyperalgesia, dental disease

Opioid-induced deaths in Australia now driven substantially by pharmaceutical opioids, not just heroin
Illicit fentanyl contamination of the heroin/counterfeit pill supply is an escalating driver of unpredictable overdose

Chronic mu-receptor agonism -> receptor downregulation/tolerance -> dose escalation -> withdrawal on cessation (locus coeruleus noradrenergic rebound)
Opioid-induced hyperalgesia: paradoxical increase in pain sensitivity with chronic high-dose use - distinct from tolerance, worsens rather than improves with further dose escalation
Chronic suppression of hypothalamic-pituitary-gonadal axis -> hypogonadism (both sexes)
Chronic GI mu-receptor effects -> persistent constipation (does not develop tolerance, unlike most other effects)

Dependence - clinical (tolerance, withdrawal, loss of control, continued use despite harm); consider validated screening (e.g. ORT for risk before prescribing)
Opioid-induced hyperalgesia - suspect when pain worsens despite dose escalation, especially with diffuse, poorly localised pain
Endocrine - testosterone/oestrogen levels if symptomatic hypogonadism (fatigue, low libido, amenorrhoea) with chronic use

Acute overdose

See toxidromes-opioid (naloxone titrated to respiration, observation, take-home naloxone)

Chronic use / dependence

See substance-use-disorder-opioids note for OAT (methadone/buprenorphine) and relapse prevention
Opioid-induced hyperalgesia: reduce/rotate opioid rather than escalating further; consider multimodal non-opioid analgesia
Prophylactic laxatives for anyone on regular opioids - constipation does not resolve with tolerance
Manage hypogonadism if symptomatic and confirmed (endocrinology input)

Dependence is a chronic relapsing condition - relapse after a period of abstinence carries high overdose risk from lost tolerance
OAT substantially reduces mortality, overdose, and blood-borne virus transmission compared with no treatment

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