What might cause unexplained weight gain in a teenage girl?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Unexplained weight gain in teenage girls often stems from hormonal shifts, and common causes include:

Birth control side effects (especially hormonal contraceptives)
Cushing's syndrome, a condition involving excess cortisol
Polycystic ovary syndrome (PCOS)
Hypothyroidism, which slows metabolism
Obesity-related factors, including lifestyle and genetics

Because these causes range from easily managed to more serious, identifying the underlying issue early matters. A free, instant, online symptom check can help clarify possible conditions in minutes, giving you a clearer picture of what may be happening and confident next steps to discuss with a doctor.

Reviewed for medical accuracy: 07/20/2026

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Explanation

Unexplained weight gain in teenage girls can have several causes:

Hormonal Changes: One potential reason is the use of hormonal birth control. Some studies suggest that hormonal contraceptives can lead to weight changes in adolescents.
Cushing's Syndrome: Another possible cause is Cushing's syndrome, a condition where the body produces too much cortisol, leading to weight gain, especially around the face and belly.
Obesity Factors: Lastly, general factors contributing to obesity can also lead to weight gain. These include lifestyle choices, genetics, and other health conditions.

If you are worried about sudden weight changes, you can use a free symptom checker to help identify possible causes and determine whether you should talk to a healthcare provider for proper guidance.

(References)

Risser WL, Gefter LR, Barratt MS, & Risser JM. (1999). Weight change in adolescents who used hormonal .... The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 10401972.
Magiakou MA, Mastorakos G, Oldfield EH, Gomez MT, Doppman JL, Cutler GB Jr, et al. (1994). Cushing's syndrome in children and adolescents. .... The New England journal of medicine, 8052272.
Pomahacova R, Paterova P, Nykodymova E, Polak P, Sladkova E, Skalicka E, & Sykora J. (2023). Overweight and obesity in children and adolescents with .... Biomedical papers of the Medical Faculty of the University Palacky, Olomouc, Czechoslovakia, 37712247.

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