Does HRT cause weight gain?

No, HRT does not cause weight gain. The weight changes women notice in midlife are driven by menopause itself and ageing, not by the treatment.

This is a common worry that puts women off HRT unnecessarily, and the evidence is reassuring: pooled data from randomised trials show no effect of oestrogen, alone or with progestogen, on body weight beyond what women gain at menopause anyway. The honest other half is that the same evidence found HRT does not prevent that gain either, so it is not a weight-loss treatment. What does cause midlife weight gain is a combination of factors that happen with or without HRT:

• Falling oestrogen, which redistributes fat to the middle
• Muscle loss with age, which lowers the calories you burn each day
• Often poorer sleep and lower activity

Note what is not on that list: a slowing metabolism. The largest study of daily energy expenditure to date found that, once you account for how much lean tissue someone carries, metabolic rate is stable from 20 to 60 with no visible menopause effect. Your metabolism has not slowed; you are simply carrying less of the muscle that was burning the calories, which is a problem you can do something about.

This is the same picture set out in menopause weight gain, and the treatment is being blamed for the timing rather than the cause. Some women do notice temporary bloating or fluid retention when starting HRT, which can feel like weight gain but is not fat and usually settles, and it sits among the other adjustment effects in HRT side effects. The type and dose can be adjusted if it bothers you, and distinguishing fluid from fat is the key, since the former passes while genuine fat gain has the causes above behind it.

The gap between perception and data is the heart of it. Because women often start HRT at exactly the age midlife weight gain sets in anyway, the two coincide and the treatment gets the blame. Controlled studies that separate the two consistently fail to pin weight gain on HRT, which is why fear of it is a poor reason to decline a treatment that could help.

What to do: do not avoid HRT for fear of weight gain, since that fear is not supported by the evidence. To manage midlife weight, focus on what works at this stage: strength training to rebuild muscle, enough protein, a Mediterranean-style diet, good sleep and limiting alcohol. If you start HRT and feel bloated, ask your GP about adjusting the regimen.

Go deeper: our full guide, does HRT cause weight gain?, walks through the trial numbers, where the myth began, and what to do if your scale is moving.