What are the most common side effects of olanzapine?

The most common side effects of olanzapine are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

Lack of energy and sleepiness

Dry mouth

Constipation 

Increased appetite

Tremor (shakes)

Restlessness 

Dizziness

Change in behavior

Teenagers (age 13-17) may experience these additional side effects.

Headache

Pain in stomach area or arms and legs

Tiredness

There may be other side effects of olanzapine that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at or by calling 866-234-2345.

While less common, the most serious side effects of olanzapine are described below, along with what to do if they happen.

High Blood Sugar. Olanzapine may increase your blood sugar levels. Talk to your healthcare provider about how to maintain healthy blood sugar levels, especially if you have diabetes. Call your healthcare provider if you have any of these symptoms of high blood sugar.

Increased thirst

Increased urination (peeing)

Increased hunger

Feeling weak or tired 

Feeling sick to your stomach 

Feeling confused 

Having breath that smells fruity

High Fats (Cholesterol and Triglycerides) in Your Blood. Olanzapine may cause high cholesterol and triglyceride levels, especially in children or teenagers. You may not have symptoms of high cholesterol or triglycerides. Your healthcare provider may check your cholesterol levels before you start olanzapine and while you are taking it.

Weight Gain. Olanzapine can increase your appetite and may cause weight gain, especially in children or teenagers. Check your weight regularly and tell your healthcare provider if you experience weight gain. Talk with your healthcare provider about how to help limit weight gain, such as by exercising and eating a healthy and balanced diet.

Movement Problems. Olanzapine may rarely cause movement problems that you cannot control in your face, tongue, or body, including shakiness, stiffness, or jerkiness. This condition is called tardive dyskinesia (TD). Call your healthcare provider right away if you develop any unusual or uncontrolled movements.

Low Blood Pressure Upon Standing (Orthostatic Hypotension) and Falls. Olanzapine may cause a sudden drop in blood pressure when standing up from a seated or lying position. To help prevent this, be careful not to get up too quickly. If you feel dizzy, sit or lie down right away until the dizziness stops, then take your time getting up again. Tell your healthcare provider right away if you have any of the following symptoms of orthostatic hypotension.

Dizziness, feeling lightheaded, or fainting upon standing

Blurred vision

Confusion

Feeling weak

Trouble Swallowing. Olanzapine may cause difficulty swallowing liquids or food. Contact your healthcare provider if you experience these symptoms. This could make you more likely to get food or liquids into your lungs.

Seizures. Some people who have taken olanzapine have reported having seizures. There are many different types of seizures and some of them are not easy to recognize. Stop taking olanzapine and call your healthcare provider if you experience any of the following signs that a seizure is happening or could happen.

Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements

Stiffening of your arms and legs

Feeling anxious, nervous, confused, or a sense of dread

Feeling dizzy or lightheaded

Falling or losing consciousness

Decreased Alertness or Coordination. Olanzapine can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how olanzapine affects you.

Blood Disorders. Olanzapine can cause blood disorders, such as low white blood cell levels (leukopenia, neutropenia, or agranulocytosis). Stop using olanzapine and get help right away if you have any of the following symptoms of blood disorders.

Fever

Shortness of breath

Pale or yellowish skin

Easy bruising or bleeding

Frequent infection

Unusual weakness or tiredness

Dizziness, lightheadedness, or feeling like you are about to pass out

Headache

Fast or abnormal heartbeat

Body Temperature Regulation. Olanzapine can affect your ability to regulate your body temperature. This could make you become very hot, especially in hot weather or after exercising a lot. You should drink water and avoid overheating and dehydration. Call your healthcare provider right away if you are severely ill and have the following symptoms of dehydration.

Excessive or no sweating

Dry mouth

Feeling very hot

Feeling thirsty 

Not able to pee

Neuroleptic Malignant Syndrome (NMS). Olanzapine may cause a rare but serious condition called neuroleptic malignant syndrome, which may cause muscle stiffness and a high fever. Stop taking olanzapine and contact your healthcare provider right away if you experience any of the following symptoms.

High fever

Muscle stiffness or rigidity, where it is hard to move

Confusion 

Changes in your breathing or heart rate

Increased sweating

Excessive Prolactin (Hyperprolactinemia). Olanzapine may cause an increased level of a hormone called prolactin in your blood. These increased levels of prolactin could lead to reproductive or bone issues. Contact your healthcare provider if you experience any of the following symptoms.

Vaginal dryness 

Irregular or no periods 

Production of breast milk when not pregnant or nursing 

Inability to get or keep an erection 

Enlarged breast size (gynecomastia) 

Decreased muscle and body hair 

Severe Allergic Reactions. Olanzapine may cause allergic reactions, including a serious specific type of allergic reaction called DRESS. DRESS stands for Drug Reaction with Eosinophilia and Systemic Symptoms. It is also sometimes called multi-organ hypersensitivity. This is a reaction that can affect multiple parts of the body including your liver, kidneys, and heart. Stop taking olanzapine and get help right away if you have any of the following symptoms of a serious allergic reaction.

Post-Injection Drowsiness (Zyprexa Relprevv). When long-acting olanzapine is injected into the muscle, it may cause you to be delirious or feel sleepy. The long-acting injection must be given by a healthcare provider and you will need to wait at least 3 hours at the clinic where you got the injection to be observed for safety.