Male Fern Drug Interactions, Uses, Effectiveness, Safety & More

Male fern comes from the rhizome and root of the plant Dryopteris filix-mas, a large fern that grows in woodlands and shady, damp areas across Europe, Asia, and North America. The underground parts were dried and made into an oily extract called an oleoresin.

For many centuries, male fern was one of the best-known herbal treatments for intestinal worms, particularly tapeworm. It was listed in old pharmacy reference books and used by doctors before modern anti-parasite drugs existed. Today it is rarely used, mainly because of its toxicity and the availability of safer, more reliable medicines.

Male fern contains compounds known as phloroglucinol derivatives, including a substance called filicin (and related acids such as filicic acid). These compounds are thought to paralyze the muscles of tapeworms, causing the worm to lose its grip on the intestinal wall so it can be passed out of the body, usually with the help of a laxative.

Much of what is known about these mechanisms comes from older laboratory studies and historical medical use rather than modern, high-quality research. The same compounds that act on worms can also be toxic to humans, which is the key reason male fern is no longer recommended.

Male fern is considered potentially poisonous. The dose needed to kill worms is close to the dose that can harm a person, giving it a very narrow safety margin. Overdose or even normal-seeming use can cause serious harm.

People with liver disease, kidney disease, heart problems, anemia, or digestive disorders should not use it. Children, older adults, and anyone who is frail are at higher risk. Pregnant women should avoid male fern entirely because of its toxicity and potential to harm the pregnancy. Breastfeeding women should also avoid it, since safety has not been established. Because of these risks, male fern should never be used for self-treatment — always consult a doctor or pharmacist, and rely on approved modern medicines instead.

Even at usual doses, male fern can cause nausea, vomiting, diarrhea, abdominal cramps, headache, and dizziness.

More serious and potentially life-threatening effects have been reported, including vision problems or even permanent blindness, breathing difficulty, irregular heartbeat, muscle weakness, liver injury, convulsions, coma, and death. Fats and oils taken at the same time can increase absorption and the risk of poisoning. If anyone shows signs of toxicity after using male fern, seek emergency medical care right away.

There is no safe, established self-care dose for male fern, and it is not recommended for home use. In the past it was given by medical professionals in carefully measured amounts under supervision, precisely because the line between an effective and a toxic dose is so thin.

If you ever encounter a product containing male fern, do not guess at a dose. Talk with a pharmacist or doctor first, and in nearly all cases choose a safer, modern alternative for treating worms.