Does Progesterone-Only Birth Control Cause Weight Gain?

I was recently prescribed progesterone-only birth control to help with bleeding. I have had my fallopian tubes removed, so this is not to prevent pregnancy. I am worried about potential weight gain. Is there any evidence that a progesterone-only IUD could have less of an effect on weight gain, since the hormones are more isolated to the uterus?
—Anonymous

Heavy uterine bleeding is not unusual among women in their 40s and 50s and can be caused by a number of factors. For some women, this bleeding is more than just a nuisance. It impacts their daily functioning and in some cases can lead to anemia and iron deficiency. Managing heavy bleeding can significantly improve how you feel.

Progesterone and progestins — progesterone-like substances — can be very effective in managing heavy uterine bleeding. They can be given in a variety of ways, including birth control pills (with or without estrogen), intrauterine devices (IUDs) — Mirena and Kyleena are common brands — implants like Nexplanon, and injections like Depo-Provera.

Many of my patients have concerns about weight gain when they start hormonal contraception. They, like you, would prefer the option least likely to impact their weight. Do progesterone-only contraceptives cause weight gain? And does the type of progesterone or progestin used or the method of delivery matter?

A Cochrane review from 2016 looked to address these questions. The researchers reviewed data from 22 studies (five were randomized controlled trials; the others were non-randomized) that included 11,450 women and assessed weight gain related to several forms of progesterone-only contraception, including progestin-only pills and progestin-eluting IUDs.

One of the included studies found a small increase in fat mass in women taking desogestrel (a type of progestin) pills compared with women taking no hormonal contraception. A second study found no difference in weight between women taking desogestrel pills and women taking norethindrone (another type of progestin) pills.

Of the four studies included assessing progestin-eluting IUDs, there was no significant change in weight found in two studies and a modest increase in body fat percentage in two of the studies.

Of the four delivery methods included (pills, IUDs, implants, and injections), depot medroxyprogesterone acetate (Depo-Provera) appears to increase weight most significantly. This weight gain seems to be more common among women and girls in their teens and 20s.

The authors note that the weight gain seen across all the forms of progesterone-only contraceptives was less than 2 kilograms (4.4 pounds) and that the quality of the data available is poor.

The upshot: There may be a small increase in weight associated with progesterone-only contraception. With the exception of progesterone injections, which may cause more weight gain, especially among younger women, the degree of weight gain is similar across all forms of progesterone-only contraception. Either method you are considering — pill or IUD — is fine.