Written by Sarah Vadeboncoeur and the CAM-Cancer Consortium.
Updated February 8, 2017

Red clover (Trifolium pratense)

Is it safe?

Safety data in women with cancer is generally lacking; the information below refers to women without cancer.

Adverse events

Red clover is generally well tolerated but has been reported to cause minor adverse effects, some occurring at doses as low as 40 mg per day. Adverse effects include: headaches, myalgia, arthralgia, nausea, and diarrhoea2, breast tenderness, swollen neck glands, dizziness, vertigo, tremor, hypertension, acne, rash, pruritis, psoriasis, bloating, constipation, mouth ulcer, sore throat, osteoarthritis, bronchitis, low platelets, reflux, epistaxis, menstrual bleeding, urinary tract infection, and vaginal thrush. Compounds and mechanisms responsible for triggering adverse events are currently unknown33. A large trial of a red clover extract (Promensil) versus placebo reported no differences in the proportion of women who experienced any adverse events and no differences in the rate of specific adverse events between groups33.


There are no reports of clinically significant drug interactions with red clover in the published literature. Red clover isoflavones can inhibit CYP IA1, CYP IBI and CYP 2C9 metabolic liver enzymes and may increase plasma levels of drugs metabolised through these pathways34.

Use of red clover concomitantly with herbs that have constituents that might affect platelet aggregation could theoretically increase the risk of bleeding in some people. These herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, horse chestnut, turmeric, and others5.

Use of red clover with oestrogenic herbs and drugs, including tamoxifen, are theoretically contraindicated as red clover may have additive or antagonistic effects5.


Some suggest testing prothrombin time and/or partial thromboplastin time prior to initiating therapy34 and avoiding its use in those with bleeding disorders2. Individuals with thyroid conditions should use caution when consuming phytooestrogens as one animal study reported higher concentrations of some thyroid hormones with red clover use1. Red clover is contraindicated during pregnancy33.

Contamination issues

There are some concerns about the potential presence of coumarins in some products or specific species of red clover which can affect bleeding time. It is therefore contraindicated in those with bleeding disorders.


Sarah Vadeboncoeur, CAM-Cancer Consortium. Red clover (Trifolium pratense) [online document]. http://cam-cancer.org/The-Summaries/Herbal-products/Red-clover-Trifolium-pratense. February 8, 2017.

Document history

Assessed as up to date in February 2017 by Barbara Wider.
Assessed as up to date in January 2015 by Barbara Wider.
Summary first published in February 2013 by Sarah Vadeboncoeur.


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