Wait… I thought progesterone controlled the uterine lining—so why am I bleeding?
Progesterone is critical in balancing estrogen’s effects on the uterine lining.
In a normal menstrual cycle:
Estrogen builds up the uterine lining (called the proliferative endometrium).
Progesterone is produced after ovulation and stabilizes and matures the lining, converting it into a secretory endometrium—a plush, nutrient-rich environment ready for a fertilized egg to implant.
If pregnancy doesn’t happen, progesterone levels drop, and the lining sheds—this is your period.
Why Would a Woman Bleed on HRT?
One key reason we include progesterone in hormone therapy is to protect the uterine lining. Estrogen on its own can stimulate that lining to grow too much, which, if left unchecked, can lead to thickening or even increase the risk of uterine cancer. But progesterone does so much more than balance out estrogen. Its benefits go far beyond the uterus (and that deserves a whole blog post of its own).
But here’s the key part:
If enough progesterone builds up in the endometrial tissue, it can trigger a withdrawal bleed, just like in a natural cycle.
This can happen when:
You increase your progesterone dose or duration (for example, switching from 12 days/month to continuous dosing)
Or when your tissues finally "catch up" and respond to a therapeutic level of progesterone after an imbalance.
Carol Petersen, a compounding pharmacist and hormone therapy expert, explains this beautifully. She’s a strong advocate for bioidentical hormone therapy. She emphasizes that bleeding after increasing progesterone can be a sign that the endometrium is responding appropriately—it’s shedding what was previously built up, and had been left unchecked.
As Carol shared in one of our interviews, progesterone doesn’t cause uncontrolled bleeding—it prevents it when dosed correctly. Bleeding often means your uterus is doing what it should in response to hormonal cues. I highly recommend that you listen to this conversation about progesterone.
The bottom line
Progesterone doesn’t just prevent endometrial overgrowth—it also helps clear out what’s already there. When enough of it builds up in the tissue, the lining may shed, mimicking a natural menstrual cycle.
If you’re on HRT and start to bleed after increasing progesterone:
It’s usually not something to panic about.
It’s often a sign your hormones are beginning to do their job.
But: If bleeding continues or is heavy, it’s worth checking in with your provider to ensure your dose is optimal and your endometrial lining isn’t too thick.
Want to learn more about progesterone?
This webinar features guest experts Dr. Phyllis Bronson and Carol Peterson, who emphasize the importance of progesterone and address misinformation about it.