Fluoxetine/Olanzapine (Symbyax) Drug Interactions: What to Avoid and What to Tell Your Doctor

Fluoxetine/Olanzapine (Symbyax) interacts with a wide range of medications, supplements, and foods. Because it contains two active ingredients — an SSRI (fluoxetine) and an atypical antipsychotic (olanzapine) — both of which affect multiple brain pathways and liver enzymes, the interaction profile is extensive. This article covers the most important interactions every patient needs to know.

Always tell your doctor and pharmacist about every medication you take — including prescription drugs, over-the-counter medications, vitamins, herbal supplements, and recreational drugs.

Contraindicated Drugs: Do Not Take With Symbyax

The following drugs are absolutely contraindicated with Fluoxetine/Olanzapine — meaning they should not be used together under any circumstances:

MAO inhibitors (MAOIs): Including phenelzine, tranylcypromine, isocarboxazid, selegiline, and rasagiline. Combining an SSRI with an MAOI can cause serotonin syndrome — a potentially life-threatening condition. Wait at least 14 days after stopping an MAOI before starting Symbyax. After stopping Symbyax, wait at least 5 weeks before starting an MAOI (because fluoxetine has a very long half-life).

Pimozide: An antipsychotic used for Tourette syndrome. Fluoxetine can dramatically increase pimozide blood levels, which can lead to life-threatening cardiac arrhythmias (QT prolongation).

Thioridazine: A phenothiazine antipsychotic. Similarly, fluoxetine raises thioridazine levels and increases the risk of QTc prolongation and fatal arrhythmias.

Linezolid: An antibiotic that also inhibits MAO. Combined with the SSRI fluoxetine, it significantly increases the risk of serotonin syndrome. If linezolid is urgently needed, Symbyax must be stopped immediately.

Intravenous methylene blue: Also an MAO inhibitor when given intravenously. Contraindicated for the same reasons as linezolid.

Other fluoxetine or olanzapine formulations: Do not take Symbyax while also taking Prozac, Sarafem, Selfemra, Zyprexa, or any other product containing fluoxetine or olanzapine — this would result in double-dosing.

Serotonin Syndrome Risk: Drugs That Increase Serotonin

Serotonin syndrome is a dangerous drug interaction involving excessive serotonin activity. Because fluoxetine is a potent SSRI, combining it with other serotonergic drugs increases this risk. Medications to use with caution or discuss with your doctor:

Triptans (sumatriptan, rizatriptan, etc.) — migraine medications that activate serotonin receptors

Tramadol — a pain medication with serotonergic activity

Other SSRIs or SNRIs — combining two serotonergic antidepressants increases risk

St. John's Wort — an herbal supplement with SSRI-like serotonergic effects

Lithium — may increase serotonergic effects; monitor for serotonin syndrome symptoms

CYP2D6 Interactions: Fluoxetine Is a Potent Enzyme Inhibitor

Fluoxetine is one of the most potent inhibitors of the CYP2D6 liver enzyme. This enzyme metabolizes many medications — inhibiting it can cause those drugs to build up to potentially toxic levels. Drugs metabolized primarily by CYP2D6 include:

Tricyclic antidepressants (amitriptyline, nortriptyline, imipramine) — levels may increase significantly

Certain beta-blockers (metoprolol, propranolol) — enhanced blood pressure lowering effects possible

Certain antipsychotics (risperidone, aripiprazole) — levels may be elevated

Codeine and tramadol — reduced conversion to active metabolites (may decrease pain relief)

Carbamazepine: A Two-Way Interaction

Carbamazepine (Tegretol) is a common anticonvulsant and mood stabilizer that has a complex two-way interaction with Symbyax:

Carbamazepine induces CYP1A2, which metabolizes olanzapine — this DECREASES olanzapine blood levels, potentially reducing effectiveness

Fluoxetine inhibits CYP2C9 and CYP3A4, which metabolize carbamazepine — this INCREASES carbamazepine blood levels, potentially causing carbamazepine toxicity (dizziness, nausea, vomiting, vision changes)

Bleeding Risk: NSAIDs, Aspirin, and Warfarin

Fluoxetine and other SSRIs can impair platelet function by reducing serotonin uptake into platelets. This increases the risk of abnormal bleeding, especially in the GI tract. When combined with anticoagulants (warfarin) or antiplatelet agents (aspirin, NSAIDs like ibuprofen or naproxen), the risk of bleeding increases further. If you take these medications regularly, discuss this interaction with your prescriber.

CNS Depressants and Alcohol

Symbyax causes drowsiness, and combining it with other central nervous system depressants (CNS depressants) significantly amplifies this effect. Avoid or use with great caution:

Alcohol — enhances CNS depression, increases fall and accident risk

Benzodiazepines (alprazolam, lorazepam, diazepam) — potentiates sedation and orthostatic hypotension. The combination of diazepam and Symbyax specifically has been shown to increase orthostatic hypotension.

Opioids — additive CNS depression; use with extreme caution and only under close medical supervision

Sleep aids and antihistamines — additional sedation

Antihypertensive Medications

Olanzapine can cause orthostatic hypotension (a drop in blood pressure when standing). If you take antihypertensive medications (blood pressure drugs), this effect may be enhanced, increasing the risk of dizziness and falls. Your doctor may need to adjust your blood pressure medication dose.

Fluvoxamine: Increases Olanzapine Levels

Fluvoxamine (an SSRI used for OCD) is a potent CYP1A2 inhibitor and can significantly increase olanzapine blood levels when taken together. This can increase the risk of olanzapine side effects like sedation and metabolic effects.

What to Tell Your Doctor Before Starting Symbyax

Before starting Fluoxetine/Olanzapine, give your prescriber a complete list of everything you take — including over-the-counter pain relievers, herbal supplements like St. John's Wort, sleep aids, and any vitamins. Drug interactions are one of the most preventable causes of adverse effects. For information about side effects, see our Symbyax side effects guide.