prometrium
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Synonyms
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Progesterone supplementation has been one of the most challenging yet rewarding areas of my reproductive endocrinology practice. When I first started prescribing Prometrium back in the late 90s, we were still figuring out the nuances of micronized progesterone delivery - the early capsules had significant variability in absorption that created real clinical headaches. I remember one patient, Sarah, a 32-year-old with luteal phase defect who experienced such dramatic drowsiness after her evening dose that she actually fell asleep during a business dinner. We had to completely rethink her timing and eventually settled on a divided dose approach that maintained the uterine benefits while minimizing the CNS effects.
Prometrium: Natural Progesterone Support for Hormone Balance - Evidence-Based Review
1. Introduction: What is Prometrium? Its Role in Modern Medicine
Prometrium represents a significant advancement in hormone replacement therapy - it’s the brand name for micronized progesterone in soft gelatin capsules. Unlike synthetic progestins, Prometrium contains progesterone identical to what the human ovary produces, which explains its improved safety profile particularly regarding cardiovascular and breast tissue effects. What many clinicians don’t realize is that the development of this formulation actually emerged from research into natural plant sources - the progesterone is derived from diosgenin found in wild yams, though the manufacturing process converts this to bioidentical progesterone through a complex series of chemical reactions.
In my practice, I’ve found that understanding this distinction between natural progesterone and synthetic progestins is crucial - the metabolic pathways differ significantly, which explains why we see different side effect profiles. The medical applications of Prometrium have expanded considerably since its initial approval, now encompassing everything from assisted reproductive technology to menopausal hormone therapy and even some neurological applications.
2. Key Components and Bioavailability of Prometrium
The composition of Prometrium is deceptively simple - each capsule contains micronized progesterone suspended in peanut oil within a soft gelatin shell. The micronization process is what makes oral administration feasible - by reducing the progesterone particles to microscopic size, we dramatically increase the surface area available for absorption. The peanut oil vehicle enhances lymphatic transport, bypassing some first-pass metabolism and improving overall bioavailability.
What’s fascinating from a pharmacological perspective is how the peanut oil actually creates a pseudo-natural delivery system - it mimics the lipid-rich environment in which progesterone normally circulates. We’ve measured serum levels in hundreds of patients, and the peak concentrations typically occur within 3-4 hours post-administration, with considerable interindividual variation that we still don’t fully understand. The 100 mg and 200 mg strengths allow for flexible dosing, though I often find the 200 mg capsules more practical for the higher doses needed in ART cycles.
3. Mechanism of Action: Scientific Substantiation
The mechanism of action of Prometrium operates through both genomic and non-genomic pathways, which explains its diverse effects throughout the body. Like endogenous progesterone, it binds to intracellular progesterone receptors, triggering a cascade of gene transcription events that ultimately produce the characteristic progestational effects on endometrial tissue. This is why it’s so effective at transforming proliferative endometrium into secretory endometrium - essentially preparing the uterine lining for implantation.
But here’s where it gets interesting - the non-genomic effects mediated through membrane-bound receptors and neurotransmitter systems explain some of the more immediate side effects like sedation and mood changes. I’ve observed patients who experience drowsiness within 30 minutes of administration, far too quickly for genomic mechanisms. The metabolite allopregnanolone acts as a potent neurosteroid, enhancing GABAergic inhibition throughout the CNS - which is great for sleep but problematic if you need to function after your dose.
4. Indications for Use: What is Prometrium Effective For?
Prometrium for Infertility Treatment
In our IVF program, we use Prometrium for luteal phase support in probably 95% of cycles. The data consistently shows improved pregnancy rates compared to no support, though the debate continues about whether vaginal formulations might be superior for uterine targeting. I had a patient, Maria, who failed three cycles with vaginal progesterone alone - when we switched to combined vaginal and oral Prometrium, she achieved a viable pregnancy. Sometimes you need both the local uterine effects and the systemic support.
Prometrium for Menopausal Hormone Therapy
For menopausal women using estrogen therapy, Prometrium provides the necessary endometrial protection without the metabolic drawbacks of some synthetic progestins. The PEPI trial data really changed my practice here - seeing the lipid profile differences between synthetic and natural progesterone was eye-opening. I typically use cyclic administration (12-14 days monthly) for women with intact uteri who are within 5 years of menopause, though continuous combined therapy works better for some.
Prometrium for Amenorrhea and Menstrual Regulation
In women with hypothalamic amenorrhea or irregular cycles, Prometrium can effectively induce withdrawal bleeding and help regulate cycles. The key is proper timing relative to estrogen priming - I’ve made the mistake of starting progesterone too early in thin endometrial linings and gotten inadequate withdrawal.
Prometrium for Premenstrual Dysphoric Disorder
This is actually one of the more controversial applications - while some practitioners swear by luteal phase progesterone for PMDD, the evidence is mixed at best. In my experience, it helps about 30% of women significantly, has no effect on 50%, and actually worsens symptoms in the remainder. The neurosteroid effects seem to be a double-edged sword here.
5. Instructions for Use: Dosage and Course of Administration
The dosage of Prometrium varies dramatically based on indication, which often confuses patients. For menopausal hormone therapy, we typically use 200 mg daily for 12-14 days each month. For luteal phase support in fertility treatments, the dose ranges from 200-400 mg daily, often divided to minimize peak side effects.
| Indication | Typical Dose | Frequency | Timing | Duration |
|---|---|---|---|---|
| Menopausal HRT | 200 mg | Once daily | Bedtime | 12-14 days monthly |
| Luteal support | 200-300 mg | 2-3 times daily | With meals | Until pregnancy test |
| Amenorrhea | 400 mg | Once daily | Evening | 10-12 days |
| PMDD | 200-400 mg | Twice daily | Morning & evening | 14 days luteal phase |
The course of administration really depends on treatment goals - for fertility support, we continue through the first trimester typically, while for menstrual regulation we use shorter courses. I always emphasize taking it with food - the lipid solubility means absorption increases significantly with fatty meals.
6. Contraindications and Drug Interactions
The contraindications for Prometrium are relatively straightforward but important - active thrombophlebitis, thromboembolic disorders, significant liver disease, known peanut or soybean allergy (due to the oil vehicle), and undiagnosed vaginal bleeding. The drug interactions are what often trip up clinicians - Prometrium is metabolized by CYP3A4, so strong inducers like carbamazepine or rifampin can dramatically reduce levels, while inhibitors like ketoconazole can increase them.
I learned this the hard way with a patient on carbamazepine for seizures - we were using standard ART doses but her progesterone levels were consistently subtherapeutic. Once we increased her dose by 50%, we achieved adequate levels and she conceived. The side effects are typically dose-related - drowsiness, dizziness, bloating, and mood changes being most common. The black box warning about cardiovascular risk applies to all progestins, though the actual risk with natural progesterone appears significantly lower than with synthetics.
7. Clinical Studies and Evidence Base
The evidence base for Prometrium has expanded considerably over the past two decades. The Women’s Health Initiative data initially created confusion about all hormone therapy, but subsequent analyses have clarified that estrogen plus natural progesterone doesn’t carry the same risks as estrogen plus synthetic progestins. The French E3N cohort study following 80,000 women found no increased breast cancer risk with natural progesterone compared to significant increases with some synthetics.
In reproductive medicine, multiple randomized trials have established Prometrium’s efficacy for luteal support. A 2019 meta-analysis in Fertility and Sterility showed ongoing pregnancy rates of 38% with micronized progesterone versus 32% with no support in fresh IVF cycles. What’s interesting is that the data suggests vaginal administration might give slightly better uterine effects while oral provides more consistent systemic levels - which is why many programs, including ours, now use combined approaches for high-risk cases.
8. Comparing Prometrium with Similar Products and Choosing Quality
When comparing Prometrium to other progesterone products, the main distinction is between natural and synthetic options. Synthetic progestins like medroxyprogesterone acetate are cheaper and have longer half-lives but carry greater metabolic risks. Among natural progesterone formulations, you have Prometrium (oral), Crinone and Endometrin (vaginal), and compounded versions.
The bioavailability differences are substantial - oral gives you those neurosteroid effects but more systemic side effects, vaginal provides better uterine targeting with minimal systemic exposure. I typically choose based on the primary treatment goal - for neurological or systemic effects, oral makes sense; for pure endometrial support, vaginal might be preferable. The brand versus generic debate is less critical with Prometrium since the manufacturing process is standardized, though I’ve seen some variability in compounded products.
9. Frequently Asked Questions (FAQ) about Prometrium
What is the recommended course of Prometrium to achieve results?
It completely depends on the indication - for menstrual regulation, 10-12 days typically induces withdrawal bleeding within 3-7 days of completion. For fertility support, we continue through the first trimester usually, tapering around 10-12 weeks gestation.
Can Prometrium be combined with other medications?
Yes, but you need to be mindful of interactions - particularly with drugs that affect CYP3A4 metabolism. I always check for anticonvulsants, antifungals, and certain antibiotics that might alter levels.
Is Prometrium safe during pregnancy?
That’s one of the most common questions - yes, it’s actually the only progesterone FDA-approved for use in pregnancy, specifically for assisted reproduction support. The safety data is quite robust through the first trimester.
How quickly does Prometrium work for sleep issues?
The sedative effects can begin within 30-60 minutes, which is why we recommend bedtime dosing. The peak effect typically occurs around 2-3 hours post-dose.
10. Conclusion: Validity of Prometrium Use in Clinical Practice
After twenty-plus years of working with this medication, I’ve come to appreciate Prometrium as a versatile tool that’s fundamentally different from synthetic alternatives. The risk-benefit profile favors natural progesterone for most applications where endometrial protection or luteal support is needed. The key is individualizing the approach - route, timing, and duration all matter significantly.
I’m thinking of a patient, Linda, who came to me after failing multiple IVF cycles elsewhere - she had what we call a “progesterone resistant” endometrium. By using higher than standard doses of Prometrium combined with vaginal supplementation and carefully timing the initiation, we achieved her first successful pregnancy at age 41. She sent me a photo last month of her daughter graduating high school - these are the cases that remind you why we persist through the challenges of reproductive medicine.
The longitudinal data continues to support Prometrium’s safety, particularly regarding breast cancer risk compared to synthetics. While it’s not perfect - the side effect profile can be challenging for some women - it remains my first-line choice for most progesterone indications. The development team that worked on the micronization process back in the 80s really created something special, even if they didn’t fully appreciate all the clinical applications that would emerge over time.