A known heroin user stops using the drug and 12 hours later develops yawning, lacrimation, rhinorrhoea, piloerection, abdominal cramps and diarrhoea. These features reflect which underlying physiological state?

• A Acute adrenal insufficiency following chronic opioid suppression of ACTH
• B Rebound parasympathetic discharge from denervated enteric neurons
• C Rebound sympathetic overactivity unopposed by exogenous opioid ✓
• D Serotonin excess from supersensitized raphe neurons

Explanation

Chronic opioids suppress noradrenergic activity in the locus coeruleus; on withdrawal, rebound noradrenergic firing produces the classic abstinence syndrome of yawning, lacrimation, rhinorrhoea, piloerection, cramps and diarrhoea. Clonidine relieves these symptoms by suppressing locus coeruleus firing. Parasympathetic rebound, adrenal insufficiency and serotonergic mechanisms do not account for the constellation, although diarrhoea reflects increased secretions and motility driven by the adrenergic-cholinergic imbalance.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.