Can hyperthyroidism cause weight loss?

The thyroid helps regulate how quickly the body uses energy. When thyroid hormone is excessive, the body may burn more energy at rest. Appetite can increase, stay the same or fall, so weight may decrease despite eating normally. Muscle can also become weaker when the body remains overactive. Weight loss is not specific to hyperthyroidism; digestive illness, medication effects, emotional strain and other conditions can also contribute. Diarrhoea, sweating, heat intolerance, difficulty sleeping and palpitations may provide useful context. See the overview of [Hyperthyroidism](/conditions/hyperthyroidism/).

Arrange a medical review for unexplained or ongoing weight loss, especially with a fast heartbeat, tremor, heat intolerance or frequent bowel movements. Record your weight trend, appetite, bowel pattern and any changes in medicines. A clinician may examine your thyroid and request thyroid-function blood tests, while checking for other explanations. Eat regular, nourishing meals and drink enough fluid; if appetite is poor or diarrhoea is present, ask for tailored dietary advice. Avoid taking thyroid medicine or supplements differently from the prescribed plan.

Seek urgent care if weight loss occurs with fainting, severe weakness, confusion, chest pain, severe breathlessness, dehydration or a very fast irregular heartbeat. Contact a clinician soon if you cannot maintain food or fluids, have persistent diarrhoea, or notice rapidly worsening symptoms. An unexplained change deserves assessment even when you otherwise feel well.

Ask which thyroid tests are appropriate, whether your medicines could affect weight, and how to protect nutrition while symptoms are investigated. Ask what weight change or new symptom should trigger an earlier review.