Can I take Black cohosh and St John's wort together?

Why this happens

Both supplements are processed by the liver. St John's wort is a potent inducer of liver enzymes (specifically CYP3A4), which can speed up the breakdown of other substances. Furthermore, both herbs have been independently linked to rare cases of hepatotoxicity (liver damage), and taking them together may theoretically increase this risk.

What you should do

You should consult your doctor or a pharmacist before taking these two supplements together. If you do use them, watch for signs of liver trouble, such as yellowing of the eyes or skin (jaundice), dark urine, severe stomach pain, or unusual tiredness. It is also important to tell your doctor if you are taking any other prescribed medications, as St John's wort interacts with many common drugs.

Important precautions

Pregnancy

Do not use black cohosh during pregnancy. It may stimulate uterine contractions, potentially increasing the risk of miscarriage or premature labour.

Liver disease

Black cohosh has been linked to rare but serious cases of liver failure. You must stop taking it and see a doctor immediately if you develop yellowing of the skin or eyes, dark urine, or severe stomach pain.

Hormone-sensitive conditions (e.g. breast cancer)

Because black cohosh may act like the hormone oestrogen, you should not use it if you have a history of breast cancer, uterine cancer, or endometriosis without specialist medical supervision.

Depression and Mental Health

Like other antidepressants, St John's wort may increase the risk of suicidal thoughts or self-harm, particularly when first starting treatment. Seek immediate medical help if your mood worsens.

Drug Interactions

St John's wort significantly reduces the effectiveness of many essential medicines, including the contraceptive pill, blood thinners (warfarin), epilepsy medications, and organ transplant drugs. Do not start it without a pharmacist checking your current medications.

Serotonin Syndrome

Taking St John's wort with other antidepressants or triptans (for migraine) can cause serotonin syndrome, a potentially life-threatening condition involving high fever, agitation, and muscle rigidity.

Photosensitivity

St John's wort can make your skin significantly more sensitive to sunlight, leading to severe sunburn or skin reactions even with limited exposure.

Food and drink warnings

Alcohol

Black cohosh has been linked to rare but serious cases of liver damage. Because alcohol also puts strain on the liver, it is advisable to limit or avoid alcohol consumption while taking this supplement to reduce the risk of liver toxicity. St John's wort can increase the sedative effects of alcohol, making you feel more drowsy or dizzy than usual. It is best to limit or avoid alcohol while taking this herbal remedy.

Caffeine

St John's wort may increase sensitivity to caffeine. This can lead to increased feelings of anxiety, jitteriness, or a racing heart.

Foods high in Tyramine (e.g., aged cheeses, cured meats, fermented products)

Although the risk is lower than with older prescription antidepressants, St John's wort has some mild MAOI-like activity. Consuming very large amounts of tyramine-rich foods could potentially lead to a rise in blood pressure.

Using other medicines

Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.