Mental Health Blog
Olanzapine Weight Gain: Real Numbers and What Helps
How much weight people gain on olanzapine, how fast it starts, why teens gain more, and the steps with real evidence behind them.
Facts updated October 2026
- Most people gain some weight. In long studies on the FDA label, 64 in 100 adults gained at least 7 percent of their starting weight.
- The average adult gain was about 12 pounds in studies of 48 weeks or longer. Short studies showed about 6 pounds in the first 6 weeks.
- Teens gain more. In long studies, teens gained about 25 pounds on average, and 89 in 100 gained at least 7 percent.
- The first two weeks are a signal. In one study, gaining about 2 pounds by week 2 flagged most of the people who went on to gain a lot.
- There are real tools. Metformin and the combination pill Lybalvi both cut gain in trials. Never stop olanzapine on your own to lose weight.
Yes, olanzapine causes weight gain in most people who take it, and the gain is often large. The reason is simple. Olanzapine raises appetite strongly, and it can change how your body handles sugar and fat.
Olanzapine, also sold as Zyprexa, is one of the strongest medicines for schizophrenia and bipolar mania. For many people it works when other choices did not. That is why we want you to know the real numbers, not a vague warning that weight "may change."
Our full olanzapine guide covers what the medicine treats, how to take it and its other side effects. This page goes deep on one question. How much weight should you expect, and what can you do about it?
How Much Weight People Gain on Olanzapine
The FDA label gives the clearest numbers, from studies the maker ran before and after approval. In 13 placebo controlled studies of adults, people on olanzapine gained an average of 2.6 kg, about 5.7 pounds. That was over a median of 6 weeks. People on a placebo pill lost about half a pound.
Longer studies tell the bigger story. In studies lasting at least 48 weeks, the average gain was 5.6 kg, or about 12.3 pounds. Those studies followed 2,021 adults for a median of about a year and a half.
| Group on the label | Adults | Teens 13 to 17 |
|---|---|---|
| Average gain, short studies | 5.7 pounds over a median of 6 weeks | 10.1 pounds over a median of 3 weeks |
| Average gain, long studies | 12.3 pounds (48 weeks or more) | 24.6 pounds (24 weeks or more) |
| Gained 7 percent or more, long studies | 64 in 100 | 89 in 100 |
| Gained 15 percent or more, long studies | 32 in 100 | 55 in 100 |
| Gained 25 percent or more, long studies | 12 in 100 | 29 in 100 |
Put those percents into pounds. For a person who starts at 170 pounds, a 7 percent gain is about 12 pounds. A 15 percent gain is about 26 pounds. This is simple math on the label percents, not a forecast for you.
One more detail stands out. The label says meaningful gain happened in every starting weight group, from lean to heavy. Starting thin does not protect you.
How Fast the Weight Comes On
Gain on olanzapine starts early. On the label, the median time to reach a 7 percent gain was 8 weeks in adults. For a 15 percent gain, it was 12 weeks.
A 2021 review in Frontiers in Psychiatry put it plainly. The bulk of the gain tends to come in the first months of treatment. The same review cites work showing that 80 in 100 people treated early in psychosis gained 7 percent or more.
The first two weeks can also predict the rest. A 2018 study in Psychiatry Research followed people with schizophrenia who started olanzapine. A gain of 1 kg, about 2.2 pounds, by week 2 picked out 92 percent of the people who went on to gain 7 percent by week 6.
That study was small, with 67 people who finished it. Still, the lesson holds up well. Week 2 is the time to speak up, not month six, when the pounds are already there.
Much of the usual advice says weight "varies" and to eat well. Both are true. But that advice skips the timing, and the timing is the most useful fact you have.
Why Olanzapine Makes You Hungry
Olanzapine blocks histamine receptors very strongly. That same action is part of why it makes people sleepy. It also turns up hunger and dulls the feeling of being full.
People often describe it as a hunger that does not shut off. Late night snacking and bigger portions creep in without a clear choice. Feeling tired adds to it, because you move less.
Weight is not the only change. The label also shows shifts in blood sugar and blood fats. In adults on olanzapine for 48 weeks or more, 26 in 100 who started with borderline fasting sugar moved into the high range. Triglycerides can rise sharply too, sometimes above 500 mg/dL.
Those changes can happen even before the scale moves much. That is why the label asks for fasting glucose and fasting lipid tests at the start of treatment and again during it, plus regular weight checks.
Teens Gain More, So Plans Start Earlier
Olanzapine is FDA approved for some teens ages 13 to 17 with schizophrenia or bipolar mania. The label is direct about the cost. Teens gained about 10 pounds in a median of 3 weeks in short studies, nearly twice the adult gain in half the time.
In longer studies of at least 24 weeks, teens gained an average of 11.2 kg, or 24.6 pounds. The label says this higher risk of weight gain and blood fat changes may lead prescribers to try other medicines first in teens.
If your teen is starting olanzapine, ask about the plan for weight on day one. Ask how often weight and blood work will be checked. A teen's growth chart makes small changes easy to miss without a written log.
What Actually Helps
Some steps have trial data behind them. Others are common advice with less proof. The list below sorts them out.
Metformin
Metformin is a diabetes medicine that is sometimes added to fight weight gain from antipsychotics. A 2011 review in the British Journal of Clinical Pharmacology pooled four placebo controlled trials in people taking olanzapine. After 12 weeks, people on metformin weighed about 5 kg, or 11 pounds, less than people on placebo.
The 2021 Frontiers review calls metformin the option with the largest and most consistent evidence. It suggests thinking about it early in treatment. Metformin is a prescription with its own side effects, so this is a talk to have with your prescriber.
Lybalvi, the Combination Pill
Lybalvi pairs olanzapine with samidorphan, a medicine that blocks opioid receptors. It is FDA approved for schizophrenia and bipolar I disorder in adults. In a 24 week trial, people on Lybalvi gained 4.2 percent of their starting weight. People on olanzapine alone gained 6.6 percent.
The share who gained 10 percent or more dropped from 29.8 in 100 to 17.8 in 100. That is a real gain still, just a smaller one. Mayo Clinic notes the same point, that Lybalvi may bring less weight gain than olanzapine alone.
Two limits matter. Lybalvi cannot be used with opioids, including opioid pain medicines, and the label calls for a waiting period after the last dose. The trial also did not study people already stable on olanzapine, so the effect of switching is unknown.
Food, Movement and Sleep
Lifestyle plans help most when they are built for you and run by trained staff, such as a dietitian or an exercise coach, according to the Frontiers review. A handout alone does less.
- Plan your evenings. Hunger often peaks at night. Keep filling foods, like vegetables, beans and plain yogurt, ready to eat.
- Drink water, not calories. Soda, juice and sweet chai add up fast when appetite is high.
- Eat at set times. Regular meals make it easier to notice true hunger.
- Walk after meals. Short daily walks help, even when you feel tired.
- Protect your sleep. Poor sleep raises hunger. Ask about the best time of day for your dose.
Switching Medicines
Some antipsychotics carry a lower risk of weight gain. Mayo Clinic lists aripiprazole, ziprasidone, lurasidone, cariprazine and lumateperone among them. But the Frontiers review found little evidence that switching reliably undoes gain that has already happened. A switch also carries a real risk of relapse, so it is a careful decision, made together, never a quick fix.
Never stop olanzapine on your own to lose weight. Stopping suddenly can bring back voices, mania or severe agitation fast. Call your prescriber first. There is almost always a safer move.
A Simple Way to Track It at Home
You do not need fancy tools. A scale, a tape measure and a notebook are enough. The steps below are a plan you can bring to your visits.
- Weigh in before your first dose. Write down your weight and your waist size at the belly button.
- Weigh once a week, on the same day, in the morning, before eating.
- Watch week 2. If you are up 2 pounds or more, tell your prescriber at once.
- Know your 5 and 7 percent marks. Multiply your starting weight by 0.05 and 0.07, and write both numbers down.
- Note your hunger. A word or two a day, like "snacking at night," helps your prescriber see the pattern.
- Ask for your lab results. Keep your fasting glucose, A1C and lipid numbers in the same notebook.
Bring the log to every visit. Numbers on paper turn a vague worry into a clear choice about the next step.
Olanzapine Care by Telehealth in California
Weight tracking fits video visits well. You weigh in at home, share your log on screen and talk through the next step without a drive. Your lab work can be done at a nearby lab.
At Mindful Sewa Psychiatry, Harpal Singh, PMHNP-BC, provides medication management by secure video anywhere in California. That includes care for schizophrenia and bipolar disorder. Care is available in English, Punjabi, Hindi and Spanish.
If you are on olanzapine and worried about your weight, a psychiatric second opinion can help you weigh your options. We would rather plan for weight on day one than chase it later.
We are not a crisis or emergency service. In an emergency, call 911. For a mental health crisis, call or text 988, or see our crisis resources. For everything else, book an appointment or call (888) 457-8124.
Outside Sources
- ZYPREXA (olanzapine) prescribing information, on DailyMed, National Library of Medicine.
- LYBALVI (olanzapine and samidorphan) prescribing information, Alkermes, on DailyMed.
- Metformin for olanzapine-induced weight gain, a systematic review and meta-analysis, Praharaj SK and others, British Journal of Clinical Pharmacology, 2011.
- Early prediction of olanzapine-induced weight gain for schizophrenia patients, Lin CH and others, Psychiatry Research, 2018.
- Worth the Weight? Olanzapine Prescribing in Schizophrenia, Fitzgerald I and others, Frontiers in Psychiatry, 2021.
- Bipolar medications and weight gain, Mayo Clinic, November 2025.
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Questions From the Field
How much weight do you gain on olanzapine?
On the FDA label, adults gained about 5.7 pounds on average in the first 6 weeks and about 12.3 pounds in studies of 48 weeks or longer. Many people gain more than the average. In long studies, 32 in 100 adults gained 15 percent or more of their starting weight.
How quickly does olanzapine weight gain start?
It often starts in the first weeks. On the label, the median time to a 7 percent gain was 8 weeks. One study found that gaining about 2 pounds by week 2 flagged most people who would gain a lot by week 6.
Can you take olanzapine without gaining weight?
Some people gain little, but most gain some. Tracking from day one, a food and movement plan, and medicines like metformin can limit the gain. Talk with your prescriber about a plan before you start.
Does metformin stop weight gain from olanzapine?
It can reduce it. A 2011 review of four trials found people on metformin weighed about 11 pounds less than people on placebo after 12 weeks. It is a prescription with its own side effects, so your prescriber decides if it fits.
Is Lybalvi better than olanzapine for weight?
In a 24 week trial, people on Lybalvi gained 4.2 percent of their weight, compared with 6.6 percent on olanzapine alone. It still causes some gain. It cannot be used with opioids, and the effect of switching after long olanzapine use was not studied.
Will I lose the weight if I stop olanzapine?
Not always, and stopping on your own is risky. Symptoms can come back quickly. A 2021 review found little evidence that switching medicines reliably reverses weight already gained, so any change should be planned with your prescriber.
Why do teens gain more weight on olanzapine?
The label shows teens gained about 10 pounds in a median of 3 weeks, and about 25 pounds over 24 weeks or more. The reason is not fully known. The label says prescribers may consider other medicines first for teens.
Does olanzapine raise blood sugar even without weight gain?
It can. The label shows fasting sugar and triglyceride changes in some people on olanzapine. That is why fasting glucose and lipid tests are advised at the start and during treatment, along with regular weight checks.