Tansy Side Effects: What You Need to Know

Tansy is an old herbal remedy used as tea, extract, or essential oil. People used it for digestion, insect bites, and even as a folk remedy for worms. But tansy contains thujone and other compounds that can cause real problems. If you're thinking of trying tansy, know the risks and signs of trouble first.

Common and serious side effects

Short-term, low-dose use (like a mild tea) can still cause stomach upset, nausea, vomiting, and headache. Some people get skin irritation or allergic reactions after contact with tansy oil. The bigger risks come from concentrated forms: essential oils, tinctures, or high-dose supplements.

Thujone affects the brain by blocking parts of the GABA system, which can make the nervous system more excitable. That explains why serious side effects include tremors, confusion, hallucinations, and seizures. There are case reports of people developing seizures after taking strong tansy preparations. Other severe problems can include fainting, fast heartbeat, and in rare cases organ stress from poisoning.

One important risk: tansy can cause uterine contractions. Pregnant people should avoid it completely because it may lead to miscarriage. It’s also not safe for breastfeeding infants or young children.

How to use tansy more safely

Want to reduce risk? First, avoid tansy essential oil taken by mouth — it’s highly concentrated and can be toxic. If you try a mild tea, use a trusted source and short courses only. Don’t use tansy if you have epilepsy or a history of seizures, or if you take medicines that lower seizure threshold (certain antidepressants or antipsychotics). Always tell your doctor about any herbal product you take.

Check product labeling and avoid homemade extracts unless you know the dose and chemistry. If you have liver disease, immune problems, or are on multiple medicines, get medical advice first. Stop using tansy and call your doctor if you notice persistent vomiting, severe dizziness, unusual mood or thinking changes, or muscle twitching.

If someone has a seizure, loss of consciousness, severe breathing trouble, or can't be woken, call emergency services right away. Bring the product container to the hospital if possible — that helps clinicians identify the exact preparation and plan treatment.

Short answer: tansy can cause mild stomach upset but also serious neurologic problems, especially in concentrated forms. Avoid during pregnancy, avoid essential oils by mouth, and talk to your healthcare provider before using tansy if you have seizures, are on medication, or have chronic health issues.