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Not All Progesterone Is the Same: Understanding Micronized Progesterone vs. Synthetic Progestins

One of the biggest sources of confusion in menopause care is the belief that all progesterone medications are the same. They’re not... If you’re taking estrogen therapy and still have your uterus but are not using an IUD like Mirena or Liletta, you’ll also need a progestogen to protect your uterine lining. Estrogen alone can cause the lining to thicken, increasing your risk for uterine (endometrial) cancer. A progestogen balances this effect and reduces that risk. But the type of progestogen used MATTERS, a lot!.

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Articles of Interest

In Brief: Does Micronized Progesterone Relieve Perimenopausal Symptoms?

For decades, estrogen was used as a component of hormone replacement therapy to treat menopausal symptoms, including hot flashes, night sweats, and sleep disturbance; however, after several large, prospective studies (e.g., HERS, WHI) questioned the safety of long-term use of HRT, as well as its efficacy to prevent cardiovascular disease, many women have decided to avoid traditional HRT regimens. While most studies have focused on the use of estrogen to treat menopause-related symptoms, a few studies have explored the use of progesterone in this setting.

Micronized Progesterone: Why It Matters in Hormone Therapy

When we talk about hormone replacement therapy (HRT), most of the attention goes to estrogen — but progesterone is just as important for many women. If you still have your uterus and are taking estrogen, progesterone helps protect the uterine lining from overgrowth. But that’s not the only reason it’s worth talking about.

Progesterone– Switching Between Routes of Administration

Progesterone is often prescribed in conjunction with estradiol treatment in menopausal or postmenopausal women with an intact uterus for the prevention of endometrial hyperplasia and resultant endometrial cancer that is associated with estrogen treatment alone in this population. Though synthetic progestins with enhanced oral bioavailability such as medroxyprogesterone acetate are available, progesterone micronized is recommended as first line for endometrial protection given the enhanced risk of coronary heart disease (CHD) and breast cancer associated with this progestin as compared to progesterone.

Using Micronised Progesterone

In women who are menopausal and their periods have ceased, one Prometrium® capsule should be taken every evening before bed for at least 25 days per month. Most women use their Prometrium® every night of the month without a break without any issues. In women who are perimenopausal and are still having periods, Prometrium® may be dosed cyclically to try and mimic the cycle and reduce breakthrough bleeding. This approach involves taking two X Prometrium® capsules for 12 consecutive days of the month (Day 15-26) and none for the other 16-19 days of the month.

What If I Can’t Take Oral Progesterone?

Compare that to medroxyprogesterone acetate (MPA), a synthetic progestin that was used in older hormone therapy regimens, especially during the Women's Health Initiative study. While both protect the uterine lining, MPA has been associated with an increased risk of cardiovascular disease and breast cancer. Micronized progesterone, by contrast, is considered metabolically neutral—it doesn’t interfere with the beneficial effects of estrogen on cholesterol levels and hasn’t shown the same risks in studies.

Why Compounded Progesterone is Not Recommended

Dr. Mary Claire Haver does not recommend using compounded progesterone cream due to safety concerns. Progesterone is a large molecule that is difficult to get absorbed through the skin in high enough levels from compounded creams to adequately protect the uterine lining when taking estrogen. For these reasons, medical societies like ACOG and the Menopause Society are wary of compounded progesterone, and oral micronized progesterone is generally preferred.