Hypothyroidism means the thyroid gland does not produce enough thyroid hormone. Because thyroid hormone influences energy use throughout the body, hypothyroidism can contribute to weight gain—but the relationship is often misunderstood.
How much weight gain does hypothyroidism cause?
Weight gain is a recognized symptom of hypothyroidism, but thyroid disease does not usually explain very large increases in body weight by itself. Part of the increase can come from salt and water retention, not only body fat.
If substantial weight gain continues after thyroid hormone levels are normalized, other contributors—diet, activity, sleep, medicines, menopause, fluid retention or another health condition—should also be considered.
Common symptoms of hypothyroidism
NIDDK lists symptoms that can include:
- fatigue;
- weight gain;
- feeling unusually cold;
- constipation;
- dry skin or thinning hair;
- joint or muscle pain;
- heavy or irregular menstrual periods;
- depression or memory problems;
- a slower heart rate.
These symptoms are not specific to thyroid disease, so diagnosis requires appropriate blood testing rather than symptoms alone.
How is hypothyroidism tested?
Clinicians commonly measure thyroid-stimulating hormone (TSH) and thyroid hormone levels, especially free T4. In primary hypothyroidism, TSH is typically elevated because the pituitary gland is signaling the thyroid to make more hormone.
What about hyperthyroidism?
An overactive thyroid generally increases energy expenditure and more often causes weight loss, heat intolerance, tremor, a rapid or irregular heartbeat and other symptoms. The older version of our rapid-weight-gain article incorrectly suggested the opposite; that has now been corrected.
Will thyroid medication make you lose weight?
Levothyroxine replaces deficient thyroid hormone; it is not a weight-loss drug. Treating true hypothyroidism may reverse some thyroid-related weight gain, particularly fluid-related weight, but it should not be used to push thyroid levels above normal in an attempt to lose more weight.
Do not use thyroid or “metabolism” supplements as treatment
Over-the-counter products marketed as thyroid support, metabolism boosters or fat burners are not substitutes for diagnosis and treatment. Some supplements have contained thyroid hormones or stimulant ingredients that can cause harm.
When to seek medical assessment
Discuss testing with a healthcare professional if you have persistent symptoms such as unexplained weight gain combined with fatigue, cold intolerance, constipation, menstrual changes, a neck swelling or a family history of thyroid disease.
Bottom line
Hypothyroidism can contribute to weight gain, but it usually does not explain every kilogram gained. Diagnosis is based on thyroid blood tests, and treatment aims to restore normal thyroid hormone levels—not to use thyroid hormone as a weight-loss aid.
Sources
Medical note: Thyroid symptoms overlap with many other conditions. Diagnosis and medication adjustment require appropriate laboratory testing and clinical assessment.
