Zyprexa Side Effects: What to Expect and When to Call Your Doctor

Like all antipsychotic medications, Zyprexa (olanzapine) can cause side effects. Understanding what to expect — and what signs require prompt medical attention — is an important part of taking this medication safely. This guide covers olanzapine's most common side effects, its serious warnings, and what to do if you experience them.

Common Side Effects of Zyprexa (Olanzapine)

These side effects are frequently reported and often manageable with guidance from your healthcare provider:

Weight gain: One of the most common and clinically significant side effects. Many patients gain 5-10 lbs in the first months of treatment; some gain significantly more. Regular weight monitoring is important.

Sedation/drowsiness: Olanzapine is sedating, especially at higher doses. This can be beneficial if taken at night but may impair daytime alertness in some patients.

Increased appetite: Related to weight gain. Olanzapine can increase cravings for carbohydrates and calories.

Dry mouth: Due to anticholinergic effects. Staying hydrated and using sugar-free gum can help.

Constipation: Another anticholinergic effect. Increasing fiber, fluid intake, and physical activity often helps.

Orthostatic hypotension: A drop in blood pressure when standing up. This can cause dizziness, lightheadedness, or fainting, especially when first starting the medication. Rise slowly from sitting or lying positions.

Dizziness and headache: Common early in treatment and often improve over weeks.

Elevated blood sugar: Olanzapine can cause hyperglycemia, even in patients without a history of diabetes. Blood sugar monitoring is recommended, especially in higher-risk patients.

Serious Side Effects — When to Call Your Doctor or Go to the ER

Some side effects are rare but serious and require immediate medical attention:

Neuroleptic malignant syndrome (NMS): A rare but life-threatening reaction. Signs include high fever, very stiff muscles, sweating, confusion, and rapid heartbeat. Call 911 or go to the ER immediately.

Tardive dyskinesia (TD): Involuntary, repetitive movements of the face, tongue, lips, or limbs. Risk increases with duration of use. Report any abnormal movements to your doctor promptly.

Severe hyperglycemia or diabetic ketoacidosis (DKA): Symptoms include extreme thirst, frequent urination, fatigue, and fruity breath. Seek emergency care if you suspect DKA.

DRESS syndrome: Drug Reaction with Eosinophilia and Systemic Symptoms — a rare, serious allergic reaction that can affect the liver, kidneys, and heart. Symptoms include fever, rash, and flu-like symptoms. Stop the medication and seek immediate care.

Stroke or TIA (in elderly patients with dementia): Zyprexa carries a boxed warning that elderly patients with dementia-related psychosis have an increased risk of death and cerebrovascular events. Olanzapine is not approved for this population.

Post-injection delirium/sedation (Zyprexa Relprevv only): Long-acting injectable olanzapine can cause sedation and delirium within hours of injection. Patients must be observed for at least 3 hours after each injection at a REMS-certified facility.

Metabolic Monitoring: What Lab Tests You May Need

Because olanzapine affects metabolism, your provider should monitor the following, typically at baseline and periodically during treatment:

Weight and BMI

Fasting blood glucose and HbA1c

Fasting lipid panel (cholesterol and triglycerides)

Blood pressure

If you're not sure when your last labs were, ask your prescriber at your next appointment.

Can Side Effects Be Managed?

Many of olanzapine's common side effects can be managed without stopping the medication. Your prescriber may:

Adjust your dose if side effects are dose-related (like sedation)

Add dietary counseling and exercise support for weight and metabolic management

Consider switching to Lybalvi (olanzapine/samidorphan) to reduce weight gain while maintaining olanzapine's efficacy

Switch to a different antipsychotic with a more favorable metabolic profile if side effects are intolerable

Always talk to your prescriber before making any changes to your medication. See our post on Zyprexa drug interactions for more on what else can affect your safety while on olanzapine.

If you're having trouble filling your prescription, medfinder can help you find Zyprexa in stock near you.