The short explanation
Yes, that is quite possible. An underactive thyroid can cause some weight gain, mostly from fluid and a slower metabolism, but once thyroid levels are brought into the normal range with treatment, the thyroid is usually no longer the main thing holding weight on. Many people expect a large weight drop after starting thyroid treatment, but usually only a modest change happens. If your TSH is well controlled, other common factors are more likely to be involved, such as eating patterns, low physical activity, poor sleep, stress, PCOS, insulin resistance or certain medicines. This is frustrating, but it also means there are other areas you can work on with your doctor.
What depends on your situation
The parts of this that change from woman to woman. Uncertainty is stated, not hidden.
- Ask your doctor how your TSH and free T4 compare with the target range; sometimes small adjustments are needed.
- Weight loss usually requires a combination of food changes and activity over months.
- If you have irregular periods, acne or excess hair, ask about PCOS, which often affects weight.
What this answer cannot determine
The boundary of online education. These need a clinician who can see you.
- This cannot tell you why you are not losing weight. Your doctor can review your tests, medicines and lifestyle.
Questions for your clinician
Take these with you. You can add any of them to an appointment card.
- Is my thyroid treatment at the right level?
- Could PCOS or insulin resistance be affecting my weight?
- Could any of my medicines be contributing?
- Can I see a dietitian?
When to seek help
Clinician-approved guidance for this topic. When in doubt, being seen is never the wrong choice.
Book an appointment soon
- See a doctor within a few days if you have rapid weight gain with swelling, breathlessness or extreme tiredness.
Raise it at a routine appointment
- Book a routine appointment to review your thyroid tests and plan weight management.
Sources
The evidence this explanation is built on.
- Underactive thyroid (hypothyroidism) NHS
- Weight control MedlinePlus (US National Library of Medicine)
- Polycystic ovary syndrome (PCOS) NHS
Who wrote and reviewed this
Every AskHer answer names its author. A clinically reviewed answer also names the clinician who signed it off — if no clinician is named below, it has not been clinically reviewed.
- Author
- AskHer Editorial (AI-assisted draft) AskHer's editorial team — not an individual clinician Works in English, தமிழ், हिन्दी
- Clinical reviewer
- Nobody yet No clinician has signed this answer off, and no person on the editorial team has read it yet. That is what the “Written with AI assistance” label means. It is queued for an editor to read, and then for a clinician who works in this area. The sources it was drafted against are listed above.
- Review status
- Written with AI assistance — not yet reviewed by a person
- Last reviewed
- Not yet reviewed by a person
- Version
- 1
Correction history
Substantive changes are listed, not quietly edited away.
No corrections have been made since this answer was first published.
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