Dydrogesterone has been on the market for a very long time, often sold as Duphaston. Why do some women take this type of progesterone during early pregnancy, and could you benefit from Duphaston?
What Is Dydrogesterone And What Is It Used For?
Dydrogesterone, also sold under the brand name Duphaston, is a progestin — a synthetic version of the hormone progesterone that is used for many gynecological conditions. Duphaston has been in use since the 1960s. 
You'll find progestins in birth control pills and hormone replacement therapy, for instance. Duphaston, concretely, is used to help conditions caused by progesterone insufficiency. These include:
- Dysmenorrhea (painful periods)
- Endometriosis (in which the tissues that line the uterus also grow outside of it)
- Secondary amenorrhea (where your periods have stopped occurring)
- Irregular menstrual cycles
- Dysfunctional uterine bleeding, that is, bleeding that happens when it shouldn't
- Infertility caused by a luteal insufficiency 
New uses are still being discovered — research shows that the administration of Duphaston can reduce the risks involved in having an amniocentesis, for example. 
Why Do Some Women Take Duphaston During Early Pregnancy?
In the case of a threatened miscarriage, the usual dosage is 40 mg of Duphaston right away, followed by 10 mg every eight hours until the danger passes. Women with a history of recurrent miscarriage may be prescribed 10 mg of Duphaston twice a day until their twentieth week of pregnancy. 
How effective is Duphaston at preventing miscarriage in women with a history of unexplained recurrent miscarriage? Research reveals mixed results, with some studies finding that the administration of Dydrogesterone doesn't contribute to such women's chances of having a baby very much , and others finding that Duphaston makes a significant difference .
Following several miscarriages, testing for hormonal deficits can help you get to the bottom of their case, allowing your healthcare provider to determine what may help you prevent another miscarriage more easily . Women whose repeated miscarriages are found to be linked to low progesterone levels are those who are most likely to benefit from Duphaston. It may still help women who, after testing, still don't know why they are having miscarriages, however. 
Duphaston has been discontinued in several countries, including the United States and United Kingdom, for commercial reasons. In the process, the World Health Organization did note that it is unclear how effective the drug is in preventing miscarriage, as research is both contradictory and often outdated, not in line with today's scientific standards. 
What Side Effects Does Duphaston Have?
The most common side effects of Duphaston are migraine headaches and nausea, along with tender breasts and menstrual irregularities (exactly of the kind it's also used to treat!). Duphaston also occasionally causes dizziness, vomiting, allergic reactions, weight gain, and liver problems. Other side effects are extremely rare.
Is Duphaston safe during pregnancy?
Since this is a frequently asked question, we'll tackle that too. Duphaston has been used in over 10 million pregnancies thus far, meaning there's a very large sample to draw conclusions for. There's absolutely no evidence that Dydrogesterone is harmful to fetuses. There have been suggestions — but no definite evidence — that fetal exposure to progestogens in general can lead to a higher incidence of hypospadias, a condition in which the urethral opening isn't at the tip of the penis. Hypospadias can be corrected surgically. [9, 10]
Since it is not clear whether Duphaston passes into a mother's breast milk, it is not recommended to breastfeeding mothers. 
Keep in mind that Duphaston (Dydrogesterone) is a prescription medication. Even if you happen to live in a country where you can easily buy this medication without first consulting a doctor, you shouldn't do it. Only under the care of a doctor can you be sure that the benefits of Duphaston outweigh its risks in your particular case, and that it is safe for you to take this drug.
The Bottom Line
Depending on where in the world you live, it's possible that you'll be prescribed Duphaston (Dydrogesterone) if you have suffered multiple unexplained miscarriages, if you have suffered miscarriages due to a proven progesterone deficiency, or if you are facing a threatened miscarriage. Despite the fact that it's no longer used in some countries, there is no evidence that this previously widely-used drug poses any major risks to your fetus. As long as Duphaston is prescribed by a qualified doctor who is fully aware of your medical history, it is also unlikely to pose a risk to you.