PMHNP certification cheat sheet
Serotonin syndrome, NMS and anticholinergic toxicity compared
The three look-alike toxidromes, side by side.
Reviewed by a licensed nurse · 25 October 2026
Side by side
| Feature | Serotonin syndrome | Neuroleptic malignant syndrome | Anticholinergic toxicity |
|---|---|---|---|
| Cause | Serotonergic drug, often a combination | Dopamine antagonist or withdrawal of a dopamine agonist | Antihistamines, tricyclics, antimuscarinics |
| Onset | Hours | Days | Hours |
| Tone and reflexes | Clonus and hyperreflexia | Lead-pipe rigidity, slow reflexes | Normal |
| Pupils | Dilated | Normal | Dilated |
| Skin | Sweating | Sweating | Hot, dry, flushed |
| Bowel | Diarrhea, hyperactive | Variable | Reduced bowel sounds, urinary retention |
| Key lab | Usually unremarkable | High CK | Unremarkable |
| Treatment | Stop agents, benzodiazepines, cyproheptadine if needed | Stop agent, cooling, supportive, dantrolene or bromocriptine in severe cases | Supportive, benzodiazepines for agitation, physostigmine only in selected cases |
Educational content for exam preparation. It is not clinical guidance and does not replace your facility's policies, current professional guidelines or the advice of a qualified clinician.
boardreadynurse.com · NCBI StatPearls: Serotonin Syndrome · NCBI StatPearls: Neuroleptic Malignant Syndrome