Gaining weight when you are not trying to do so can have many causes.

Metabolism slows down as you age. This can cause weight gain if you eat too much, eat the wrong foods, or do not get enough exercise.

Drugs that can cause weight gain include:

• Birth control pills
• Corticosteroids
• Some drugs used to treat bipolar disorder, schizophrenia, and depression
• Some drugs used to treat diabetes

Hormone changes or medical problems can also cause unintentional weight gain. This may be due to:

• Cushing syndrome
• Underactive thyroid, or low thyroid (hypothyroidism)
• Polycystic ovary syndrome
• Menopause
• Pregnancy

Bloating, or swelling due to a buildup of fluid in the tissues can cause weight gain. This may be due to menstruation, heart or kidney failure, preeclampsia, or medicines you take. A rapid weight gain may be a sign of dangerous fluid retention.

If you quit smoking, you might gain weight. Most people who quit smoking gain 4 to 10 pounds (2 to 4.5 kilograms) in the first 6 months after quitting. Some gain as much as 25 to 30 pounds (11 to 14 kilograms). This weight gain is not simply due to eating more.

A healthy diet and exercise program can help you manage your weight. Talk to your health care provider or a dietitian about how to make a healthy eating plan and set realistic weight goals.

Do not stop any medicines that may be causing the weight gain without talking with your provider.

Contact your provider if you have the following symptoms with the weight gain:

• Constipation
• Excessive weight gain without a known cause
• Hair loss
• Feel cold more often than before
• Swollen feet and shortness of breath
• Uncontrollable hunger accompanied by palpitations, tremor, and sweating
• Vision changes

Your provider will perform a physical exam and calculate your body mass index (BMI). The provider may also ask questions, such as:

• How much weight have you gained? Did you gain the weight quickly or slowly?
• Are you anxious, depressed, or under stress? Do you have a history of depression?
• What medicines do you take?
• What other symptoms do you have?

You may have the following tests:

• Blood tests
• Tests to measure hormone levels
• Nutritional assessment

Your provider may suggest a diet and exercise program or refer you to a dietitian. Weight gain caused by stress or feeling sad may require counseling. If weight gain is caused by a physical illness, treatment (if there is any) for the underlying cause will be prescribed.

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Kumar RB, Aronne LJ. Obesity. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 7.

Maratos-Flier E. Obesity. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 40.

Updated by: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.