Short answer: The trials say no. A Cochrane review of 22 randomized trials found no significant difference in weight gain between women on estrogen alone or estrogen plus progestin and women not on hormones, and concluded that hormone therapy does not add weight beyond what is normally gained around menopause. In the Premarin label's first-year data, weight gain was reported by 2 to 3% of women on Premarin and 4% on placebo.
Many women gain weight in midlife, and weight gain is listed among the possible effects in estrogen labels. The authors of the Cochrane review wrote that many women decline estrogen because of concern about weight gain. The question for trials is whether women on hormones gain more than similar women who are not.
The review pooled randomized trials that compared hormone therapy with placebo or no treatment and reported weight or body fat. It included 22 trials, with results analyzed separately for estrogen alone and for estrogen plus a progestogen.
| Comparison | Difference vs no hormones | Result |
|---|---|---|
| Estrogen alone, weight | +0.66 kg | Not significant |
| Estrogen plus progestogen, weight | -0.47 kg | Not significant |
| Estrogen plus progestogen, BMI | -0.50 | Not significant |
There was not enough data to pool waist-hip ratio, fat mass or skinfold measurements. Another 24 trials were still waiting on details from their authors when the review was written, so the pooled result rests on fewer studies than exist. The review counted trials where hormones were combined with diet, supplements or exercise, as long as there was a comparison group. The searches ran to 1998, so newer products and routes such as patches and gels are not well represented.
The Premarin label includes a table from the first year of a 2-year trial in 2,333 postmenopausal women aged 40 to 65. Weight gain was reported as a treatment-related reaction in about the same share of women at every dose as on placebo:
| Group | Women | Weight gain reported |
|---|---|---|
| Premarin 0.625 mg | 348 | 11 (3%) |
| Premarin 0.45 mg | 338 | 10 (3%) |
| Premarin 0.3 mg | 326 | 8 (2%) |
| Placebo | 332 | 14 (4%) |
The same label lists fluid retention (edema) and changes in weight, up or down, among reactions reported with estrogens in general. Fluid retention is different from fat gain and can come and go.
Because weight tends to change around menopause whether or not hormones are used, a single number is hard to read. Dose Track can log weight next to hormone doses over months, which makes a trend easier to show the prescriber than a memory of how clothes fit.
Read more on Dose Track: Menopause · Premarin side effects · Meta-analysis · Edema