Antipsychotics · Psychiatry
Quetiapine
Seroquel®(brand names vary by market)
Three different drugs depending on the dose, and a metabolic bill at all of them.
Also: modified release
Mechanism
Dose-dependent receptor occupancy: antihistamine sedation at low doses, antidepressant 5-HT and noradrenergic effects in the middle, meaningful D2 blockade only at antipsychotic doses.
Indications
- Schizophrenia
- Bipolar disorder, mania and depression
- Adjunct in major depressive disorder
Formulations
Dosing concepts
Dose defines the drug
A low bedtime dose is essentially an antihistamine; the antipsychotic dose is many times higher. Describing a patient as 'on quetiapine' says almost nothing without the dose.
Off-label sedation
It is widely used as a hypnotic, an indication it does not have and does not deserve given the metabolic and cardiac profile of long-term use.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~9% for the parent, with an active metabolite carrying much of the effect
- Half-life
- ~6 h; norquetiapine ~12 h
- Elimination
- hepatic: CYP3A4 substrate: inhibitors raise it substantially
- Protein binding
- ~83%
Adverse effects
- Sedationcommon
- Weight gain and metabolic syndromecommon & serious
- Orthostatic hypotensioncommon
- QT prolongationserious
- Extrapyramidal symptomscommonLeast of the common antipsychotics, which is a genuine advantage in Parkinson disease psychosis.
- Neuroleptic malignant syndromeserious
- Increased mortality in older adults with dementiaserious
Contraindications & precautions
Contraindications
- Concurrent strong CYP3A4 inhibitors, relative
- Known QT prolongation with other risk factors
Precautions
- Metabolic syndrome or diabetes
- Older adults
- Cardiac disease
- Falls risk
Interactions
Monitoring
Weight, waist circumference, glucose and lipids
The dominant long-term harm · Baseline, 3 months, then annually
ECG where QT risk factors exist
Dose-dependent effect
Movement examination
Less common than with other agents but not absent
Whether the indication is still valid
Off-label hypnotic use accumulates silently
Counselling points
- Take it at bedtime; it is sedating.
- Stand up slowly, especially early on.
- We will monitor your weight and blood tests: this medicine affects them.
- Do not stop it suddenly.
Clinical pearls
- Finding a low bedtime dose on an older patient's list with no psychiatric diagnosis attached is one of the most common deprescribing opportunities in geriatrics.
- Its low extrapyramidal burden makes it, with clozapine, one of the few antipsychotics usable in Parkinson disease psychosis.
References & review
- Quetiapine product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.