Mood pharmacology has a small number of ways to kill somebody, and each one announces itself with a discriminator you can find at the bedside. Tick only the findings you actually have — drug change, timing, reflexes, skin, vitals — and watch the differential re-rank itself. Then read what clinches the leader, and what would make it the other one.
Load a handover
The findings you have
The differential
The discriminator students lose marks on
Serotonin syndrome
Neuroleptic malignant syndrome
Trigger
Serotonergic agent started, raised or combined
Antipsychotic (or dopamine blocker) exposure
Onset
Hours
Days
Neuromuscular
Hyperreflexia and clonus, worse in the legs; myoclonus, shivering
Lead-pipe rigidity with hyporeflexia; bradykinesia
Creatine kinase
May rise
Markedly raised
Bowel sounds
Hyperactive, with diarrhoea
Normal or reduced
Antidote pathway
Benzodiazepines, then cyproheptadine
Dantrolene or bromocriptine
Resolution
Within about 24 hours once the agent stops
Days to weeks
One sentence to carry. Fast and jumpy is serotonin; slow and stiff is neuroleptic. Both are hot, confused and unstable — so the reflexes and the clock are what you examine first.
Lithium is a salt, and the kidney cannot tell the difference
Coarse tremor is the one to notice. A fine tremor can be a benign early effect. A new coarse tremor, with vomiting, drowsiness or unsteadiness, is the level climbing — hold the dose and get a stat level before you do anything else.
Two more that are not emergencies but change everything
The activation window. Physical side effects of an SSRI appear in days; the mood effect takes two to four weeks and sometimes six. In between, energy and drive can return before hopelessness lifts — which is why every antidepressant carries a boxed warning for increased suicidal ideation and behaviour in people under 25 during early treatment and dose changes. The answer is not to withhold the drug. It is closer contact, weekly check-ins, a written safety plan and asking the person directly at every visit.
Priapism on trazodone. Teach one sentence: an erection lasting more than four hours, or any painful erection, means emergency care now. It is a surgical emergency and delay costs function permanently.