For decades, “HRT” meant one thing: a pill containing Premarin (Estrogen) and Provera (Progestin). These are Synthetic Hormones. Today, they have a bad reputation. People call them “Horse Urine” or “Chemicals.” But millions of women still take them, and for some, they are actually the better choice. It is important to separate the fear from the pharmacology.
What is “Synthetic”?
“Synthetic” does not mean “Fake.” It means the molecule has been altered slightly from nature to make it more potent, longer-lasting, or patentable.
1. Conjugated Equine Estrogens (CEE)
- Brand Name: Premarin.
- Source: Yes, it comes from the urine of pregnant mares. It contains a complex mix of over 10 different estrogens.
- The Difference: It is not identical to human estradiol. However, it is incredibly potent. Because it is a mix, some women find it controls hot flashes better than the “pure” bioidentical estradiol.
2. Synthetic Progestins
- Brand Names: Provera (Medroxyprogesterone Acetate), Norethindrone, Levonorgestrel (in the Mirena IUD).
- The Difference: These mimic progesterone, but they are chemically closer to testosterone.
- The Effect: They are very strong. They are excellent at thinning the uterine lining and preventing bleeding (often better than bioidentical progesterone).
The Risks: Why We Shifted
The shift away from synthetics came from the Women’s Health Initiative (WHI) study. The study found that the specific combination of Premarin + Provera was linked to a slightly higher risk of:
- Breast Cancer: This risk was driven primarily by the Provera (synthetic progestin), not the estrogen.
- Blood Clots/Stroke: Because these were oral pills, they were processed by the liver, increasing clotting factors.
So, Why Use Them?
If Bioidenticals are safer, why does Route B still exist?
1. Heavy Bleeding Control Bioidentical Progesterone (Prometrium) is a gentle sedative. It is great for sleep, but it is sometimes too weak to stop heavy perimenopausal bleeding. Synthetic Progestins (like the Mirena IUD or Provera pills) are the heavy artillery. If you are flooding through your clothes, you need the synthetic strength to stop the flow.
2. Convenience and Cost Bioidentical therapy often involves two separate prescriptions (a patch + a pill). Synthetic HRT often comes in a single tiny pill (like Prempro). For a busy woman who hates patches or forgets pills, the single synthetic pill is easier. It is also often much cheaper on insurance.
3. Tolerance Some women simply don’t absorb patches well, or they get skin irritation. Others feel “sedated” or groggy on bioidentical progesterone. For these women, synthetic oral HRT is a valid, effective option that gives them their life back.
The Middle Ground: The Mirena IUD
The most popular “Route B” option today is the Hybrid Approach:
- Estrogen: Bioidentical Patch (Safe, transdermal).
- Progesterone: Synthetic IUD (Mirena).
This gives you the safety of bioidentical estrogen with the bleeding control and convenience of a synthetic progestin, but because the IUD stays in the uterus, the systemic risk is lower than taking a Provera pill.
Synthetic is not “poison.” It is just a stronger tool. Sometimes, you need the power drill, not the screwdriver.