What’s the Difference Between Progestin and Progesterone?

What is the difference between progestin and progesterone? I sometimes hear them used interchangeably, but I find it confusing — is progesterone the same thing that’s in a progestin-only birth control pill?

—Anonymous

This is one of those times when using language imprecisely can be confusing. Progesterone and progestin are two slightly different things that are used in the same way. If they aren’t used carefully, it can be hard to know whether the difference matters. So let’s discuss the differences and whether they matter or not.

Progesterone is a hormone made in the ovary and placenta. It is synthesized from cholesterol through a series of steps. There are several other hormones that are also synthesized from cholesterol and are similar in chemical structure, including estrogen, testosterone, and cortisol.

Injection needles, birth control pills and a flower — Areeya Ann / Getty

A progestin is any progesterone-like substance made outside the body. Micronized progesterone (Prometrium) is identical to the progesterone our bodies make. Other progestins are chemically very similar to progesterone, so they can bind to the progesterone receptor and act like progesterone.

There are many different progestins, each chemically slightly different from both progesterone and from each other. There are reasons to choose one progestin over another depending on what indication you are using it for and how you want to take it — orally, vaginally, through the skin, in an IUD, or injected into the muscle.

Different progestins are more or less likely to bind to other receptors such as the testosterone receptor, which can then cause side effects like acne. If you are looking for progestin pills, you can find many different forms, including micronized progesterone, medroxyprogesterone, norethindrone, and drospirenone, just to name a few. If one doesn’t work well for you, another one might. This can be as simple as switching pills. When it comes to IUDs, the options are more limited. All progestin-eluting IUDs use the same progestin, levonorgestrel.

The takeaway: Progestins are synthetic progesterone-like molecules. Micronized progesterone is identical to the progesterone that our body makes, but all other progestins are slightly different.