Medication · hrt estrogen

Supplements and Conjugated oestrogens.

Every documented pair, every citation. Below: 2 documented pairs grouped by mechanism.

Conjugated oestrogens, sold under the brand names Premarin, Prempak-C, is hormone replacement therapy (oestrogen component) for menopausal symptoms.

Conjugated oestrogens is hormone replacement therapy (the oestrogen component). UK prescribing has shifted substantially since the early 2000s WHI trial retreat. Transdermal oestradiol is now the preferred delivery route over oral conjugated equine oestrogens, because the VTE and stroke risk signals were largely associated with the oral route. The supplement surface for the transdermal route is small, because the gut wall and first-pass liver metabolism are bypassed. Oral oestrogen formulations remain in CYP3A4 territory. St John's Wort is flagged by the BNF for potentially reduced efficacy. Symptom relief supplements often co-used during HRT (black cohosh, soya isoflavones, red clover, evening primrose oil) sit on top of HRT without strong interaction signals. The evidence base for any of them as additive benefit is modest. Vitamin D and calcium status matter for the bone density conversation.

Below are the 2 documented pairs we have explicitly assessed against Conjugated oestrogens in the Distil database: 1 red and 1 amber. The pairs cluster around 2 mechanisms: CYP3A4 induction and Hormonal axis modulation. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.

Documented interactions

CYP3A4 induction

Red St John's Wort

St John's Wort can reduce circulating oestrogen levels by speeding up its breakdown. For people taking HRT with conjugated oestrogens (Premarin, Prempak-C), this can mean returning menopausal symptoms (hot flushes, sleep disruption) despite a dose that was previously working, and breakthrough bleeding is a warning sign. We treat this as a do-not-combine pair without specialist sign-off.

PMID 14663455 · PMID 27444983 · BNF: Hypericum · BNF: Conjugated-oestrogens

Reviewer-flagged: awaiting clinical-reviewer sign-off.

Hormonal axis modulation

Amber Vitex

Vitex (chasteberry) acts on the body's hormone signals: it lowers prolactin and, in lab studies, gently nudges oestrogen and progesterone receptors. HRT with conjugated oestrogens works by topping up your hormones to ease menopausal symptoms, so in theory vitex could pull against that, and the HRT could equally blunt what vitex is meant to do. There is no study showing this actually happens, so it is a caution rather than a firm warning. If you take HRT, it is worth mentioning vitex to your prescriber before adding it.

PMID 7890021 · PMID 14974442 · PMID 18204102 · PMID 39519010 · BNF: Conjugated-oestrogens

Reviewer-flagged: awaiting clinical-reviewer sign-off.

What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.

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For adults over 18. This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.

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