Comfrey is a plant. Even though this plant contains poisonous chemicals called pyrrolizidine alkaloids (PAs), some people use the leaf, root, and root-like stem (rhizome) to make medicine.

Despite safety concerns, comfrey is used by mouth for stomach ulcers, heavy menstrual periods, diarrhea, bloody urine, cough, bronchitis, cancer, and chest pain (angina). It is also used as a gargle for gum disease and sore throat.

Comfrey is applied to the skin for ulcers, wounds, muscle soreness, bruises, rheumatoid arthritis, varicose veins, gout, and fractures.

What is Comfrey?

Comfrey is a perennial herb found in moist grasslands in western Asia as well as in North America. It has bell-shaped red-violet or yellowish flowers. It may contain small amounts of toxic pyrrolizidine alkaloids.

What is it used for?

Comfrey has been cultivated as a green vegetable and has been used as an herbal medicine for more than 2,000 years. Comfrey original name, knit bone, derives from the external use of poultices of its leaves and roots to heal burns, sprains, swelling, and bruises. In Western Europe, comfrey has been used topically for treating inflammatory disorders such as arthritis, gout, and thrombophlebitis, and internally for treating diarrhea. Comfrey has been claimed to heal gastric ulcers and hemorrhoids, and to suppress bronchial congestion and inflammation. Commercial comfrey sale and distribution is restricted in Germany and Canada because of its substantial toxicity.

What is the recommended dosage?

Oral use of comfrey is not recommended because of potential liver damage. Additionally, because its alkaloids are absorbed through the skin, use of comfrey as a poultice should not exceed an exposure of 100 mcg/day of the alkaloids. Limited trials have evaluated the effectiveness of alkaloid-free preparations for external use; however, these studies did not examine how much liver damage occurred in patients.

Contraindications

Comfrey is not recommended for internal use because of the liver damage caused by its pyrrolizidine alkaloids. Patients with hypersensitivity or allergic reactions to the plant should also avoid external use. Definitely do not use during pregnancy or nursing, with infants, and if you have liver or kidney disease.

Side Effects

The internal or extensive topical use of comfrey cannot be recommended because of numerous reports of liver damage.

How to use the healing herb comfrey

‘Once known as knit bone, Symphytum officinale has a long history of wound healing.’ Photograph: GAP Photos//Christa Brand

My back is a little broken. I blame it on a bag of compost, although my chiropractor blames it on all the tapping I do at the computer. If I’m to harvest potatoes and plant pumpkins, I need a plan of action, a multi pronged, throw‑everything-at-it approach: chiropractor, shiatsu massage, if necessary, painkillers – and comfrey.

Comfrey may not be an obvious choice, but it has always been such a kind plant to the garden that it should come as no surprise that is kind to the body, too. Once known as knitbone, Symphytum officinale has a long history of wound healing, particularly broken bones, torn muscles, sprains and aches. It was even applied internally, although many herbalists are cautious of using it this way because it contains powerful pyrrolizidine alkaloids that can cause liver damage and abdominal distress. However, only slight absorption occurs with external application. As such, a compress or poultice is considered more suitable for home use.

Part of comfrey magic is down to the presence of allantoin, a chemical that stimulates cell production and thus supports wound-healing. I have read that it was even used in the same way for plants: if a branch was damaged or a graft needed to be hurried along, a wrapping of comfrey was called for to do its wonders.

Its other use, of course, is as a plant food. For every 1kg of leaves, you need 15 litres of water, but it doesn’t need to be precise. Cut the leaves 5cm from the ground, fill a container, add the water and wait four weeks. Then use this liquid on any plant that needs nourishment: once a week for tomatoes, chillies, aubergines, cucumbers, and other fruit in pots once the flowers appear; every other week for other crops in pots and whenever anything in the ground needs a little boost. The leaves are rich in nitrogen, potassium and phosphorous because comfrey extensive tap root can mine all the good stuff deep in the soil.