Can I take Glucosamine and St John's wort together?

Why this happens

Glucosamine is primarily used by the body to build cartilage and does not significantly affect the liver enzymes (Cytochrome P450) that St John's wort is known to influence. St John's wort works by altering brain chemicals and speeding up the breakdown of certain medicines in the liver, but it does not interfere with how the body processes glucosamine.

What you should do

You can take these supplements together. However, always inform your doctor or pharmacist about all supplements you are taking, especially as St John's wort can interact with many prescription medicines (such as blood thinners, antidepressants, and the contraceptive pill).

Important precautions

Shellfish allergy

Many glucosamine supplements are derived from the shells of crustaceans. If you have a shellfish allergy, you must check the label for a shellfish-free (vegetarian) version to avoid a serious allergic reaction. Vegan or shellfish-free versions are available.

Asthma

Glucosamine may worsen asthma symptoms or cause increased wheezing. If your asthma symptoms become harder to control after starting this supplement, you should stop taking it immediately.

Diabetes

Glucosamine is an amino sugar and may affect your blood glucose levels. You should monitor your blood sugar more closely when starting or changing your dose.

Taking Warfarin (blood thinner)

Glucosamine can significantly increase the blood-thinning effect of warfarin, which increases your risk of serious bleeding. Do not take glucosamine with warfarin unless specifically monitored by your doctor.

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.

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.

Contraception and other medications

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

Surgery and anaesthesia

St John's wort can cause dangerous interactions with anaesthetics and must be stopped at least two weeks before any planned surgical procedure.

Food and drink warnings

Alcohol

It is best to avoid or strictly limit alcohol while using glucosamine. While there is no direct interaction, alcohol can contribute to inflammation or stomach irritation, which may counteract the benefits of the supplement.

It is best to avoid or strictly limit alcohol while taking St John's wort. Combining them can increase drowsiness and dizziness, and may increase the risk of a rare but serious reaction called 'serotonin syndrome'.

Caffeine (Coffee, Tea, Energy Drinks)

St John's wort can increase your sensitivity to caffeine. This may lead to feelings of anxiety, a racing heart, or difficulty sleeping. It is best to limit your caffeine intake.

Foods high in Tyramine (Aged cheeses, cured meats, soy sauce, yeast extracts like Marmite)

While less common than with older antidepressants, St John's wort may interact with tyramine-rich foods, potentially causing a sudden, dangerous rise in blood pressure. If you experience a severe headache or chest pain after eating these foods, seek medical help.

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.