Quetiapine vs Olanzapine: Key Differences in Use, Side Effects, and Choice

When doctors choose between quetiapine, an atypical antipsychotic used for schizophrenia and bipolar disorder and olanzapine, another atypical antipsychotic often prescribed for similar conditions, it’s not just about the diagnosis—it’s about the person. Both are used to treat schizophrenia and bipolar disorder, a mental health condition involving extreme mood swings, but they don’t act the same way in the body. One might help you sleep better. The other might make you gain weight faster. Neither is "better"—but one might be better for you.

Quetiapine, sold as Seroquel, tends to be more sedating, especially at lower doses. People often use it for trouble sleeping or anxiety alongside psychosis. Olanzapine, known as Zyprexa, is stronger at controlling active psychotic symptoms like hallucinations or delusions, but it’s also more likely to cause big weight gain and higher blood sugar. Studies show people on olanzapine gain, on average, 4–5 pounds more in the first few months than those on quetiapine. That’s not just a number—it affects confidence, heart health, and whether someone keeps taking the medicine. Quetiapine has a lower risk of metabolic side effects, but it can cause dizziness or low blood pressure when standing up. Olanzapine doesn’t usually do that, but it can raise cholesterol and triglycerides more sharply.

Both drugs can cause tremors, dry mouth, or constipation, but the balance of risks is different. If you’re already struggling with weight or have diabetes, quetiapine might be the safer pick. If your symptoms are severe and you need strong control, olanzapine might work faster—but only if you can manage the side effects. Doctors often start with one and switch if it doesn’t fit. Neither is a magic bullet. What matters is matching the drug’s profile to your life, your body, and your goals. Below, you’ll find real comparisons from people who’ve used both, side-by-side reviews of how they affect daily function, and what to watch for when switching or starting either one.