Endometrin begins absorbing through the vaginal lining shortly after insertion, with progesterone levels in the blood peaking around 8 to 12 hours after a single dose. The insert itself is small and dissolves relatively quickly, but the full absorption process takes several hours as progesterone gradually enters your bloodstream through the surrounding tissue.
How Quickly Progesterone Enters Your System
After you insert an Endometrin tablet, the progesterone doesn’t hit your bloodstream all at once. According to FDA clinical pharmacology data, a single 100 mg dose reaches peak blood levels at roughly 8 hours, with some variation from person to person (the average in clinical trials was about 8 hours, plus or minus 3 to 4 hours). So for most people, absorption ramps up over the first few hours and peaks somewhere between 5 and 12 hours post-insertion.
Once you’ve been taking Endometrin for a day or so, your body reaches a steady state, meaning progesterone levels stay more consistent throughout the day rather than sharply rising and falling with each dose. This is one reason the medication is prescribed two or three times daily: the overlapping doses keep your progesterone levels within the range needed to support early pregnancy.
What Happens to the Physical Insert
The tablet itself dissolves inside the vaginal canal as moisture breaks it down. You may notice a chalky or gritty discharge afterward, which is normal. This residue is the inactive filler material from the tablet, not unabsorbed progesterone. The progesterone absorbs directly through the vaginal walls (a process called mucosal absorption), so the medication is working even as the leftover filler makes its way out.
Some people worry that discharge means the medication “fell out” or didn’t work. In reality, the active ingredient absorbs locally through the tissue. The waxy or powdery residue you see later is expected and doesn’t indicate a problem with absorption.
How Long to Lie Down After Insertion
The FDA prescribing information for Endometrin doesn’t specify a required rest period after insertion. That said, many fertility clinics recommend lying down for 10 to 15 minutes afterward to help keep the insert in place while it begins to dissolve. This is a practical suggestion rather than a pharmacological requirement. The vaginal tissue absorbs progesterone effectively whether you’re lying down or upright, but staying horizontal briefly can reduce the chance of the tablet shifting before it softens.
If your schedule doesn’t allow you to lie down (for instance, if you’re inserting your midday dose at work), don’t stress. The insert is designed to stay in the upper vaginal canal, and absorption occurs regardless of your position.
Does Physical Activity Affect Absorption
A common concern during IVF and fertility treatment is whether exercise, swimming, or sex might interfere with how well vaginal progesterone absorbs. A prospective randomized trial specifically tested whether sexual intercourse reduced progesterone absorption from vaginal inserts. The results showed no significant difference in serum progesterone levels whether participants had intercourse (with or without a condom) or abstained entirely. Progesterone levels remained comparable across all groups.
The concern made theoretical sense: sexual activity can temporarily change the vaginal environment’s pH and moisture levels, which could theoretically affect drug absorption. But in practice, it didn’t matter. Normal daily activities, including walking, light exercise, and going about your routine, are not expected to interfere with absorption either.
Standard Dosing and Duration
Endometrin is prescribed as a 100 mg vaginal insert taken two or three times daily. Treatment typically begins on the day of egg retrieval in an IVF cycle and continues for up to 10 weeks. Spacing your doses evenly throughout the day helps maintain consistent progesterone levels. For a twice-daily schedule, morning and bedtime doses are typical. For three times daily, morning, afternoon, and bedtime is a common pattern.
If you miss a dose or insert it later than planned, the steady-state effect means your levels won’t drop dramatically from a single delayed dose. That said, keeping a consistent schedule gives your body the most stable hormonal support during the critical early weeks of treatment.
Signs the Insert Is Working Normally
You can generally expect some vaginal discharge throughout your time on Endometrin. This can range from white and chalky to slightly watery. Some people also experience mild bloating, breast tenderness, or drowsiness, all of which are effects of elevated progesterone rather than signs of a problem. These side effects actually suggest the medication is absorbing and doing its job.
If the tablet comes out intact shortly after insertion (within the first few minutes, before it has a chance to dissolve), reinserting a new one is reasonable. But once 15 to 20 minutes have passed and the tablet has softened, the progesterone is already being absorbed into the tissue, even if residue appears later.