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Olanzapine

Prescription ·Strong evidence ·Reviewed May 2026

Prescription second-generation (atypical) antipsychotic approved for schizophrenia, bipolar I disorder (manic or mixed episodes), and in combination with fluoxetine for treatment-resistant depression. Highly effective for psychotic symptoms but carries the highest metabolic risk among atypical antipsychotics, including significant weight gain, dyslipidemia, and risk of new-onset diabetes. Dosage must be determined by your prescribing physician.

Evidence tier
Strong
Indexed sources
10 2008–2024
Interactions
4
Category
Prescription
Read the sources → Compare profiles
What it's good for
  • Strong psychotic symptom control
  • Bipolar mania treatment
  • Treatment-resistant depression (with fluoxetine)9,2
  • Acute agitation management
  • Anti-emetic properties8,10
What to watch for
  • Significant weight gain
  • Drowsiness and sedation
  • Hyperglycemia and diabetes risk
  • Known hypersensitivity to olanzapine1,2
  • Do not use IM olanzapine with parenteral benzodiazepines1,2

The bottom line

Evidence rating strong. Most-documented uses: strong psychotic symptom control, bipolar mania treatment, treatment-resistant depression (with fluoxetine). 10 sources indexed (2008–2024), with 4 interaction records on file.

The science

How it works, mechanistically.

Core mechanism

Antagonizes multiple neurotransmitter receptors including dopamine D1–D4, serotonin 5-HT2A/2C/3/6, histamine H1, muscarinic M1–M5, and alpha-1 adrenergic receptors. The broad receptor binding profile accounts for both its clinical efficacy and significant metabolic side effects. 5-HT2C and H1 antagonism are particularly implicated in weight gain and metabolic effects.

Class
Atypical Antipsychotic
Absorption
Fat-soluble; take with food
Dosing

Dosing & protocol.

Common range
5–20 mg daily (as prescribed by your physician)
Recommended form
Tablet, orally disintegrating tablet, or intramuscular injection

Can be taken with or without food. Well absorbed orally. IM injection available for acute agitation.2

Safety

Full safety detail.

Side effects

  • Significant weight gain
  • Drowsiness and sedation
  • Hyperglycemia and diabetes risk
  • Dyslipidemia
  • Orthostatic hypotension
  • Dry mouth
  • Constipation
  • Elevated prolactin

Contraindications

  • Known hypersensitivity to olanzapine1,2
  • Do not use IM olanzapine with parenteral benzodiazepines1,2
  • Uncontrolled diabetes (relative)
Interactions

Interaction records.

SeriousConflict

St. John's Wort

St. John's Wort induces CYP1A2, the primary metabolic pathway for olanzapine. This can reduce olanzapine levels, causing psychotic relapse.

Recommendation: Avoid St. John's Wort with olanzapine.

SeriousConflict

Cannabis (THC-Dominant)

THC-dominant cannabis can undermine olanzapine treatment by increasing relapse risk and worsening psychosis outcomes. Systematic reviews link continued cannabis use in psychosis with more relapse, poorer adherence, and antipsychotic treatment failure. The combination can also add impairment and sleepiness in people already sensitive to olanzapine sedation.

Recommendation: Avoid THC-dominant cannabis while taking olanzapine for psychosis or mood stabilization. If cannabis use continues, your prescriber should know so relapse risk, adherence, and sedation can be monitored. Dose timing separation is not a reliable safety strategy.

SeriousCaution

Alcohol

Alcohol can add to olanzapine-related sedation, slowed reaction time, dizziness, and impaired coordination. Olanzapine can already cause sleepiness and orthostatic symptoms, so alcohol increases the chance of falls, unsafe driving, blackouts, and accidental injury. The risk is higher during dose starts or increases, in older adults, or with other sedating medicines.

Recommendation: Avoid alcohol while taking olanzapine, especially during titration or if you already feel sleepy. If you drink despite this, do not drive or use machinery and do not take extra sedatives. Seek urgent help for severe confusion, slow breathing, repeated falls, or inability to wake.

InfoSynergy

Melatonin

Melatonin has been studied as an adjunct to reduce some metabolic side effects of olanzapine, including weight and cardiometabolic changes. Randomized trials and meta-analyses suggest possible benefit, but the effects are modest and do not replace diet, activity, or metabolic monitoring. Melatonin may also add bedtime sleepiness in patients who already feel sedated on olanzapine.

Recommendation: Use melatonin with olanzapine only as an adjunct, preferably at bedtime and with your prescriber's awareness. Continue routine weight, glucose, lipid, and blood-pressure monitoring. Reduce or stop melatonin and ask for guidance if morning grogginess, falls, or worsening daytime sedation occurs.

Search all 4 interaction records for Olanzapine →

Sources

Sources, by evidence tier.

Numbered references. Citations throughout the page link here.

Meta-analyses & systematic reviews

6

Reviews & position papers

1
  • 7Olanzapine: review of safety 2008Needs reviewPMIDKantrowitz JT, Citrome L · Expert opinion on drug safety · 2008

    Kantrowitz JT, Citrome L. Olanzapine: review of safety 2008. Expert opinion on drug safety. 2008

Reference material

3
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