Progesterone suppositories deliver the hormone progesterone directly through the vaginal lining to thicken the uterus and support pregnancy. They’re most commonly prescribed during fertility treatments like IVF, to prevent miscarriage in early pregnancy, and to reduce the risk of preterm birth in women with a short cervix. Some women also use them as part of hormone replacement therapy during menopause.
How They Work in the Body
Progesterone is a hormone your body naturally produces after ovulation. Its main job is to prepare and maintain the uterine lining so a fertilized egg can implant and grow. When your body doesn’t produce enough on its own, or when a medical procedure disrupts normal hormone production, suppositories step in to fill that gap.
The vaginal route has a notable advantage over oral progesterone pills. When you swallow progesterone, your digestive system and liver break down a large portion of it before it ever reaches your uterus. This is called first-pass metabolism, and it significantly reduces how much active hormone gets where it needs to go. Vaginal suppositories bypass the liver entirely. The progesterone absorbs directly through the vaginal lining and travels to the uterus through what researchers call the “first uterine pass effect,” a preferential transport route from the vagina to the uterus. This means vaginal suppositories deliver higher concentrations of progesterone to the uterine lining than you’d expect based on blood levels alone.
The suppository base also dissolves slowly, creating a reservoir effect that releases progesterone steadily over hours rather than in a single spike. This produces more stable hormone levels across a full 24-hour period compared to oral forms.
Supporting Pregnancy During IVF
The most common reason women are prescribed progesterone suppositories is luteal phase support during IVF or other assisted reproductive treatments. During IVF, the egg retrieval process disrupts the ovary’s ability to produce progesterone naturally. Without supplementation, the uterine lining won’t develop properly, and an embryo is unlikely to implant successfully.
The typical protocol starts the day after egg retrieval, with 100 mg inserted vaginally two to three times daily. Treatment continues through the early weeks of pregnancy, usually up to 10 to 12 weeks, until the placenta has developed enough to take over progesterone production on its own. Your fertility clinic will tell you exactly when to stop.
Preventing Preterm Birth
For women with a short cervix (typically discovered on a mid-pregnancy ultrasound), vaginal progesterone can significantly lower the chance of delivering too early. A National Institutes of Health study found that progesterone reduced the rate of preterm birth before 33 weeks by 45 percent in at-risk women. In that study, only 8.9 percent of women using progesterone delivered before 33 weeks, compared to 16.1 percent in the placebo group.
The exact mechanism isn’t fully understood, but progesterone appears to help keep the cervix stable and reduce the inflammatory signals that can trigger early labor.
Reducing Miscarriage Risk
Women who have experienced previous miscarriages may be prescribed progesterone suppositories in early pregnancy. UK guidelines from NICE recommend starting vaginal progesterone at the first sign of bleeding and continuing through 16 weeks of pregnancy. The logic is straightforward: low progesterone can prevent the uterine lining from sustaining a pregnancy, and supplementation corrects that.
This use is distinct from IVF support, where the timeline is shorter (10 to 12 weeks). For miscarriage prevention, the 16-week endpoint reflects the duration used in clinical trials that showed benefit.
Hormone Replacement Therapy
Women taking estrogen during menopause need progesterone to protect the uterine lining. Estrogen alone can cause the lining to thicken excessively, a condition called endometrial hyperplasia that raises the risk of uterine cancer. Progesterone counteracts this by triggering the lining to shed regularly.
Vaginal progesterone is sometimes used for this purpose, though it’s worth noting that many vaginal formulations aren’t specifically licensed for endometrial protection in menopause. Progesterone gels and creams can have variable absorption, which makes it harder to guarantee consistent lining protection. Your prescriber will choose the form and dose based on your specific situation.
What to Expect When Using Them
Progesterone suppositories are small, waxy inserts that you place high in the vaginal canal, typically at the same time each day. A few practical realities that most women want to know about:
- Leakage is normal. The suppository base melts at body temperature, and some of it will come back out. This doesn’t mean the medication isn’t working. Enough progesterone absorbs through the vaginal lining before the residue exits.
- Lie down for 20 minutes after insertion. This gives the suppository time to dissolve in place and improves absorption.
- Increased vaginal discharge is expected. You’ll likely notice more clear discharge than usual throughout treatment. This is a normal effect of progesterone on vaginal mucus production.
- Timing around procedures matters. On the day of an embryo transfer, many clinics recommend inserting the suppository rectally that morning rather than vaginally, then returning to vaginal use afterward.
Side effects can include bloating, breast tenderness, headaches, and drowsiness, all of which mirror the symptoms of naturally elevated progesterone in the second half of your menstrual cycle. The vaginal route tends to produce fewer systemic side effects than oral progesterone because less of the hormone circulates through your bloodstream.
Vaginal vs. Oral Progesterone
The key difference comes down to where the progesterone ends up. Oral progesterone gets heavily metabolized by the liver, converting much of it into breakdown products before it reaches the uterus. These metabolites can cause more drowsiness and mood effects. Vaginal suppositories deliver progesterone directly to the target organ, achieving higher uterine tissue concentrations with lower blood levels. For fertility and pregnancy applications, this targeted delivery is why the vaginal route is strongly preferred. For menopause-related use, oral micronized progesterone remains the more commonly prescribed and licensed option in many countries.