Prometrium Food & Supplement Interactions: A Complete Clinical Guide

Prometrium is the brand name for oral micronized progesterone, a bioidentical progestogen capsule (100 mg and 200 mg) suspended in peanut oil and used mainly for endometrial protection during estrogen-based hormone therapy and for secondary amenorrhea. It is not the same molecule as synthetic progestins such as medroxyprogesterone acetate (MPA), and that distinction matters for interactions, because micronized progesterone generates a sedating metabolite that MPA does not.

The core answer: Prometrium interacts with food and supplements through two separate mechanisms that require different management. Taking it with food increases absorption, so bedtime dosing with a meal is the FDA-labeled approach. Grapefruit and St. John's Wort act on the CYP3A4 enzyme that clears progesterone, in opposite directions, and the St. John's Wort interaction is the one clear "avoid" on this page. Separately, supplements that act on the GABA-A receptor (valerian, kava, high-dose melatonin, alcohol) can add to Prometrium's own sedating metabolite, allopregnanolone, which is a dose-response and fall-risk issue rather than a metabolic one. Most other common supplements (magnesium, vitamin D, calcium citrate) have no known interaction with progesterone at typical supplement doses.

Why food changes the dose you actually absorb

The FDA-approved prescribing information for Prometrium describes a substantial food effect: taking the capsule with food increases absorption compared with a fasted state, which is the basis for the standard once-daily bedtime dosing instruction taken with an evening meal, as described in FDA-approved prescribing information. Older pharmacokinetic literature on oral micronized progesterone is often cited to attach a specific magnitude (a commonly repeated figure is a roughly 173% increase in AUC with a high-fat meal versus fasting). We are not able to verify that specific number against a primary source we can link with confidence here, so treat the percentage as a figure that needs confirmation against the current label text rather than a settled fact. What is established is the direction and clinical relevance: taking Prometrium fasted on some days and with food on others will produce inconsistent blood levels, and consistency in how you take it matters more than which specific meal composition you choose.

Bedtime dosing with food also has a practical rationale beyond absorption: it places the peak sedative effect during sleep rather than during waking hours.

Grapefruit, Seville orange, and the CYP3A4 question

Progesterone is metabolized primarily through hepatic CYP3A4. Grapefruit and Seville orange contain furanocoumarins that inhibit intestinal CYP3A4, an effect the FDA has described generally for CYP3A4 substrate drugs (FDA consumer update on grapefruit juice). Because progesterone is a CYP3A4 substrate, the plausible effect of grapefruit consumed close to a Prometrium dose is higher, less predictable progesterone exposure, which could mean more pronounced sedation or other dose-related effects. This is a mechanistically reasonable extrapolation from the general CYP3A4 warning rather than a progesterone-specific clinical trial finding, and it should be presented to readers that way. Regular navel oranges and typical orange juice do not contain meaningful furanocoumarin levels and are not part of this concern.

St. John's Wort: the one supplement with a clear "avoid"

St. John's Wort (Hypericum perforatum) is a well-documented inducer of CYP3A4 and P-glycoprotein, an effect established for multiple CYP3A4-substrate medications in interaction studies. Applied to progesterone, sustained CYP3A4 induction would be expected to lower progesterone exposure meaningfully, which matters clinically because inadequate progesterone activity while estrogen therapy continues raises the theoretical risk of unopposed endometrial stimulation. We could not verify a progesterone-specific interaction trial to attach a precise percentage reduction to this claim, so the safest framing is: St. John's Wort is a known strong CYP3A4 inducer, progesterone is a known CYP3A4 substrate, and the combination is one a prescriber should be told about rather than one a patient should manage alone. Because enzyme induction is a sustained effect on enzyme synthesis, spacing the two agents apart during the day does not remove the interaction. Anyone using St. John's Wort for mood symptoms who is starting or continuing Prometrium should discuss this with the prescribing clinician before combining them, and stopping St. John's Wort abruptly can itself change drug levels, so that decision should also go through the prescriber.

Sedating supplements: an additive-effect problem, not a metabolic one

Prometrium's active metabolite, allopregnanolone, is a positive modulator of the GABA-A receptor, the same receptor targeted by benzodiazepines. This is the accepted mechanism behind Prometrium's sedative side-effect profile and is described in the neurosteroid literature broadly, though we are not citing a specific PubMed identifier here because the exact source could not be verified against the claim.

Several common supplements act on the same receptor system:

• Valerian root contains valerenic acid, described in the literature as a GABA-A modulator. Combined with Prometrium at bedtime, the plausible effect is additive sedation, which raises fall-risk concern in older women in particular.
• Kava kava also acts on GABA-A pathways and separately has been associated with reports of hepatotoxicity that are independent of any sedation interaction, a concern noted by regulators in the past.
• Alcohol is a GABA-A modulator as well. Combining it with a bedtime Prometrium dose plausibly deepens sedation beyond what either produces alone.
• Melatonin is different: it is metabolized mainly through CYP1A2 rather than CYP3A4, so there is no clear metabolic conflict with progesterone. The concern with melatonin is purely additive sedation at higher doses (5 to 10 mg), not a pharmacokinetic interaction. A lower starting dose (0.5 to 1 mg) is a reasonable way to use melatonin alongside Prometrium if a clinician agrees it is appropriate.

None of these combinations are absolute contraindications on their own. The concern scales with dose, with age, and with whether the person already has other sedation risk (sleep apnea, other CNS-active medications, mobility issues).

Supplements with no established interaction

Magnesium (glycinate, citrate, or oxide, typically 200 to 400 mg per day) does not inhibit or induce CYP3A4 at supplemental doses, and the NIH Office of Dietary Supplements does not list a known interaction with steroid hormones (NIH ODS magnesium fact sheet). Vitamin D is metabolized through CYP27B1 and CYP24A1, not CYP3A4, and the NIH fact sheet similarly does not describe a progesterone interaction (NIH ODS vitamin D fact sheet). Calcium citrate does not require gastric acid for absorption and is flexible in timing; calcium carbonate does, and separating it from Prometrium by an hour is a reasonable, low-cost precaution even though it is not confirmed by a specific trial.

Black cohosh, saw palmetto, and DHEA are commonly used by perimenopausal women and are sometimes described online as having progesterone interactions. We could not verify progesterone-specific pharmacokinetic data for any of the three strong enough to state a defined interaction. What can be said honestly: black cohosh's mechanism of action is debated and it is not established as a meaningful CYP3A4 modulator at standard doses, though rare hepatotoxicity case reports exist for black cohosh in general (independent of Prometrium) and support periodic liver-function checks with long-term use. Saw palmetto has weak 5-alpha-reductase inhibiting activity in vitro, which is theoretically relevant because progesterone is partly metabolized via that same enzyme to allopregnanolone, but there is no established clinical-dose interaction to report. DHEA raises circulating estrogens peripherally in postmenopausal women, which is a reason to monitor estradiol and progesterone levels if DHEA is added, rather than a direct progesterone interaction.

Peanut allergy: a real contraindication, not a supplement issue

Prometrium capsules are formulated in peanut oil, and the FDA label carries a contraindication for patients with known peanut hypersensitivity. For patients who need micronized progesterone but cannot tolerate peanut oil, compounded micronized progesterone in alternative oil bases is sometimes used. Compounded preparations are not FDA-approved, are not subject to the same manufacturing oversight, and can vary batch to batch, a distinction described in FDA's compounding guidance (FDA compounding policy). This is a decision for the prescriber, not a self-directed substitution.

Older adults and liver disease: where the stakes are higher

Sedation from allopregnanolone, layered onto GABA-A-active supplements, is a plausible and clinically meaningful fall-risk factor in women over 65, consistent with general geriatric prescribing caution around GABA-A-active agents, though Prometrium itself is not a benzodiazepine and is not on standard high-risk medication lists in the same category. In hepatic impairment, reduced CYP3A4 and CYP2C19 capacity would be expected to slow clearance of progesterone and its metabolites, which is a pharmacologic inference from how the liver handles steroid metabolism generally rather than a Prometrium-specific outcome trial. The Endocrine Society's hormone therapy guidance recommends general caution with hormonal therapies in active liver disease (Endocrine Society clinical practice guidelines). Anyone with known liver disease should have this discussed explicitly with the prescribing clinician, including which supplements add hepatic burden (kava and high-dose black cohosh are the two on this page worth flagging).

What guideline bodies say about micronized progesterone generally

Menopause society guidance has generally favored micronized progesterone over some synthetic progestins for certain metabolic and tolerability reasons. ACOG's guidance on menopausal symptom management similarly notes that the choice of progestogen affects tolerability and metabolic effects (ACOG practice bulletin on menopausal symptoms). We are paraphrasing rather than quoting these documents directly because the exact wording in the source material we started from could not be verified against the primary documents; readers who need the precise language should consult the linked guidance directly.

Evidence boundary: what is established versus what is plausible

Established: Prometrium's food effect is real and is the basis for FDA-labeled bedtime, with-food dosing. St. John's Wort is a genuine CYP3A4 inducer and progesterone is a genuine CYP3A4 substrate. Prometrium's sedation is mediated through allopregnanolone acting on GABA-A receptors. Peanut oil is a real contraindication for peanut-allergic patients. Grapefruit's furanocoumarin-driven CYP3A4 inhibition is an established general mechanism.

Plausible but not established with progesterone-specific trial data on this page: the exact magnitude of the food effect and the St. John's Wort effect on progesterone levels specifically; additive sedation risk with valerian, kava, or alcohol as a quantified (rather than mechanistic) risk; saw palmetto's effect on allopregnanolone generation at supplement doses; DHEA's net effect on the estrogen-progesterone balance.

Not established: any claim that black cohosh, magnesium, vitamin D, or calcium citrate meaningfully change progesterone levels. No dosing or monitoring instruction in this article should be used to self-adjust a Prometrium regimen; changes should go through the prescribing clinician.

A decision framework for a bedtime Prometrium dose

Use this to decide whether a food or supplement choice needs a conversation with your prescriber, a timing adjustment, or no action at all.

Step 1: Is the substance a CYP3A4 inducer or inhibitor? If yes (St. John's Wort = inducer; grapefruit, Seville orange = inhibitor), this changes how much active drug is in your system, not just how sleepy you feel. St. John's Wort should not be combined with Prometrium without prescriber input, because reduced progesterone exposure can undermine endometrial protection. Grapefruit close to your dose is avoidable rather than mandatory to eliminate entirely; keep at least a 4-hour gap if you use it regularly.

Step 2: Is the substance GABA-A active (valerian, kava, alcohol, high-dose melatonin)? If yes, the question is additive sedation and fall risk, not drug failure. Lower the dose of the second agent, avoid combining two at once, and be more cautious if you are over 65, live alone, or already take another CNS-active medication.

Step 3: Does it require gastric acid for absorption (calcium carbonate)? If yes, separate by about an hour as a low-cost precaution, even without trial-level confirmation that it matters.

Step 4: Is it magnesium, vitamin D, or calcium citrate? No known interaction at supplement doses. Take on your normal schedule.

Step 5: Is it a supplement with theoretical but unconfirmed pharmacodynamic overlap (black cohosh, saw palmetto, DHEA)? Continue if your clinician is aware you take it, and bring it up if you have long-term use of black cohosh (liver-function monitoring) or are adding DHEA (estradiol and progesterone monitoring).

Next step regardless of category: if you develop breakthrough bleeding, unusual daytime sedation, or a fall, that is a reason to contact your clinician promptly rather than adjust the supplement or the dose yourself. This article does not provide individualized dosing advice.

When to seek urgent care

New or worsening abnormal bleeding, chest pain, sudden severe headache, leg swelling or pain, vision changes, or signs of a fall-related injury while on hormone therapy warrant urgent evaluation rather than a wait-and-see approach, regardless of what supplement was recently added or removed.