Associated with adverse drug interactions - mental state changes

Red flags

New psychosis/mania in a patient started on corticosteroids, dopamine agonists, or stimulants
Confusion + fever + rigidity - NMS/serotonin syndrome, not primary psychiatric decompensation
Suicidal ideation emerging after starting an antidepressant (esp. under 25 - black box warning, close early monitoring)
Delirium in the elderly after starting/increasing an anticholinergic drug

Anticholinergic drugs -> delirium

TCAs, first-generation antihistamines, oxybutynin, some antipsychotics - anticholinergic burden accumulates across the drug list

Steroid-induced mental state change

Corticosteroids - mood elevation, mania, psychosis, insomnia; dose-dependent, usually within days to weeks

Dopaminergic

Levodopa, dopamine agonists (pramipexole, ropinirole) - psychosis, impulse control disorders (gambling, hypersexuality)

Sedative/withdrawal

Antidepressant-related

SSRI/SNRI - activation syndrome (agitation, insomnia) especially in early treatment and in the young; rare induction of hypomania in undiagnosed bipolar disorder

Other

Beta-blockers (depression - weaker evidence than historically taught), isotretinoin (depression/mood change - warned but causality debated), varenicline (historically flagged, evidence since reassuring), interferon (depression)

Timeline relative to new drug/dose change
Personal/family history of bipolar disorder (antidepressant-induced switch risk)
Steroid dose and duration
Collateral history for behaviour change, impulse control symptoms (gambling, hypersexuality on dopamine agonists)

Mental state exam - mood, thought form/content, perceptual disturbance
Delirium screen (attention, fluctuation, level of consciousness) vs primary psychiatric presentation
Vital signs, tone, reflexes - exclude serotonin syndrome/NMS masquerading as psychiatric agitation

Exclude organic cause first - glucose, UEC, calcium, TSH, infection screen, CT if focal/first presentation
Drug levels where relevant (lithium, digoxin)
Review full medication list for cumulative anticholinergic burden

Identify and stop/taper the causative agent where possible rather than adding an antipsychotic reflexively
Steroid-induced mania/psychosis - dose reduction if clinically feasible, antipsychotic if severe/dose cannot be reduced
Anticholinergic delirium - deprescribe, supportive care
Antidepressant-induced activation/suicidality - close review, consider dose/agent change, do not simply stop abruptly (discontinuation syndrome)
Dopamine agonist impulse control disorder - dose reduction, switch to levodopa monotherapy if severe

New psychiatric symptoms in a patient on a new drug are a drug effect until excluded, not automatically a primary psychiatric relapse
Anticholinergic burden is cumulative across multiple "safe" drugs - no single agent may look causative in isolation
Under-25s starting antidepressants need closer early follow-up given the suicidality signal, but this should not deter appropriate treatment
Dopamine agonist impulse control disorders are frequently concealed by patients out of shame - ask directly

1. New drug, new mental state - assume causation first

"I look for the temporal link to a new prescription before assuming psychiatric relapse."

2. Add up the anticholinergic burden

"No single drug looks dangerous alone, but four mildly anticholinergic drugs together can cause delirium in an elderly patient."

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