Dizziness, stomach pain, dry mouth, constipation, weight gain, drowsiness may occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly. To minimize dizziness or fainting, stand up slowly when arising from a seated or lying position; especially when you first start using this medication. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor immediately if any of these serious side effects occur: fast heartbeat, ankle/leg swelling, agitation, confusion, restlessness, weakness, difficulty speaking, numbness or tingling of hands or feet, trouble walking (abnormal gait), painful menstrual periods, pink urine, tremor. Tell your doctor immediately if any of these unlikely but serious side effects occur: yellowing of the eyes or skin, painful urination, other eye problems, seizures, difficulty swallowing, signs of infection (such as fever, persistent sore throat). Seek immediate medical attention if any of these unlikely but serious side effects occur: chest pain, weakness on one side of the body, sudden vision changes, headache. This drug may infrequently make your blood sugar level rise, which can cause or worsen diabetes. High blood sugar can rarely cause serious conditions such as diabetic coma. Tell your doctor immediately if you develop symptoms of high blood sugar, such as unusual increased thirst and urination. If you already have diabetes, be sure to check your blood sugars regularly. This drug may also cause significant weight gain and a rise in your blood cholesterol (or triglyceride) levels, especially in teenagers. These effects, along with diabetes, may increase your risk for developing heart disease. Discuss the risks and benefits of treatment with your doctor. (See also Notes section.) This medication may rarely cause a serious condition called neuroleptic malignant syndrome (NMS). Seek immediate medical attention if you develop the following: fever, muscle stiffness, severe confusion, sweating, fast or irregular heartbeat. Olanzapine may rarely cause a condition known as tardive dyskinesia. In some cases, this condition may be permanent. Tell your doctor immediately if you develop any unusual/uncontrolled movements (especially of the face or tongue). In rare instances, this medication may increase your blood level of a certain hormone (prolactin). For females, this rare increase in prolactin levels may result in unwanted breast milk, the menstrual period stopping, or difficulty becoming pregnant. For males, it may result in decreased sexual ability, inability to produce sperm, or enlarged breasts. If you develop any of these symptoms, tell your doctor immediately. For males, in the very unlikely event you have a painful or prolonged erection lasting 4 or more hours, stop using this drug and seek immediate medical attention, or permanent problems could occur. A serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.