Knitbone; Symphytum officinale
Comfrey ( Symphytum officinale ) is sometimes used on the skin to treat wounds and reduce inflammation from sprains and broken bones. Comfrey roots and leaves contain allantoin, a substance that helps new skin cells grow, along with other substances that reduce inflammation and keep skin healthy. Comfrey ointments have been used to heal bruises as well as pulled muscles and ligaments, fractures, sprains, strains, and osteoarthritis.
In the past, comfrey was also used to treat stomach problems. However, it has toxic substances called pyrrolizidine alkaloids that damage the liver and can lead to death. Comfrey is no longer sold in the U.S., except in creams or ointments. The United Kingdom, Australia, Canada, and Germany also have banned the sale of oral products containing comfrey.
The dangerous substances in comfrey are also absorbed through the skin, so harmful amounts may build up in the body. Be careful if you use an ointment containing comfrey (see How to Take It section), and never use comfrey on broken skin.
Comfrey is a perennial shrub that is native to Europe and some parts of Asia. Fond of moist soils, comfrey has a thick, hairy stem, and grows 2 to 5 feet tall. Its flowers are dull purple, blue or whitish, and densely arranged in clusters. The leaves are oblong, and often look different depending on where they are on the stem. Lower leaves are broad at the base and tapered at the ends while upper leaves are broad throughout and narrow only at the ends. The root has a black outside and fleshy whitish inside filled with juice.
Comfrey preparations are made from the leaves or other parts of the plant grown above the ground. New leaves tend to have more of the poisonous pyrrolizidine alkaloids than older leaves. Some preparations were also made from the roots, but roots contain up to 16 times the amount of pyrrolizidine alkaloids.
What is it Made Of?
Comfrey contains substances that help skin regrow, including allantoin, rosmarinic acid, and tannins. It also has poisonous chemicals called pyrrolizidine alkaloids.
Oral comfrey products have been banned in the U.S. and many European countries, but you can still find creams and ointments for the skin.
Comfrey ointments (containing 5 to 20% comfrey), creams, poultices, and liniments are made from the fresh or dried herb, leaf, or root of comfrey species. Use only products made from leaves of common comfrey.
Be sure to buy comfrey products from companies with good reputations. Follow dosage recommendations below.
How to Take It
Never give a child comfrey by mouth. DO NOT put creams or ointments with comfrey on a child's skin.
- Never take comfrey by mouth. Severe liver poisoning and even death may occur.
When using herb and leaf ointments, creams, and other preparations for the skin, follow these safety recommendations:
- Never apply comfrey to broken skin.
- Use only small amounts of creams with comfrey for no longer than 10 days at a time.
- DO NOT use any comfrey product for more than 4 to 6 total weeks in one calendar year.
Comfrey has toxic substances that can cause severe liver damage and even death. You should never take comfrey by mouth.
The toxic substances in comfrey can be absorbed by the skin. Even creams and ointments should be used for only a short time, and only under a doctor's supervision.
DO NOT use comfrey on open wounds or broken skin.
DO NOT use comfrey if you have liver disease, alcoholism, or cancer.
Children, the elderly, and pregnant or breastfeeding women should not use comfrey products, even ones for the skin.
Since comfrey may increase the risk of liver damage, it should not be used with other medications that may also affect the liver, such as acetaminophen (Tylenol). If you take any medications, whether prescription or over the counter, ask your doctor before using comfrey.
You should not use some herbs that have also been known to cause liver problems, such as kava, skullcap, and valerian, while using comfrey ointments or creams.
Barna M, Kucera A, Hladíkova M, Kucera M. Randomized double-blind study: wound-healing effects of a Symphytum herb extract cream (Symphytum×uplandicum Nyman) in children. Arzneimittelforschung . 2012 Jun;62(6):285-9. doi: 10.1055/s-0032-1308981.
Bleakley CM, McDonough SM, MacAuley DC. Some conservative strategies are effective when added to controlled mobilisation with external support after acute ankle sprain: a systematic review. Aust J Physiother . 2008;54(1):7-20.
D'Anchise R, Bulitta M, Giannetti B. Comfrey extract ointment in comparison to diclofenac gel in the treatment of acute unilateral ankle sprains. Arzneimittelforschung . 2007;57(11):712-6.
Frost R, MacPherson H, O'Meara S. A critical scoping review of external uses of comfrey (Symphytum spp.). Complement Ther Med . 2013;21(6):724-45.
Frost R, O'Meara S, MacPherson H. The external use of comfrey: a practioner survey. Complement Ther Clin Pract . 2014;20(4):347-55.
Grube B, Grunwald J, Krug L, Staiger C. Efficacy of comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee: results of a double-blind randomised, bicenter, placebo-controlled trial. Phytomedicine . 2007;14(1):2-10.
Koll R, Klingenburg S. Therapeutic characteristance and tolerance of topical comfrey preparations. Results of an observational study of patients. Fortschr Med Orig . 2002;120(1):1-9.
Miller LG. Herbal medicinals: selected clinical considerations focusing on known or potential drug-herb interactions. Arch Intern Med . 1998;158(20):2200-2211.
Miskelly FG, Goodyer LI. Hepatic and pulmonary complications of herbal medicines. Postgrad Med J . 1992;68:935-936.
Pabst H, Schaefer A, Staiger C, Junker-Samek M, Predel HG. Combination of Comfrey Root Extract Plus Methyl Nicotinate in Patients with Conditions of Acute Upper or Low Back Pain: A Multicentre Randomised Controlled Trial. Phytother Res . 2012 Aug 8. doi:10.1002/ptr.4790.
Ridker PM, Ohkuma S, McDermott WV, Trey C, Huxtable RJ. Hepatic venocclusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology . 1985;(88):1050-1054.
Smith DB, Jacobson BH. Effect of a blend of comfrey root extract (Symphytum officinale L.) and tannic acid creams in the treatment of osteoarthritis of the knee: randomized, placebo-controlled, double-blind, multiclinical trials. J Chiropr Med . 2011 Sep;10(3):147-56. doi: 10.1016/j.jcm.2011.01.003.
Staiger C. Comfrey: a clinical overview. Phytother Res . 2012 Oct;26(10):1441-8. doi: 10.1002/ptr.4612.
Staiger C. Comfrey root: from tradition to modern clinical trials. Wien Med Wochenschr . 2013;163(3-4):58-64.
Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr . 2000;3(4A):501-508.
Weston CFM, Cooper BT, Davies JD, et al. Veno-occlusive disease of the liver secondary to ingestion of comfrey. Br Med J . 1987;295:183.
Yeong ML, Swinburn B, Kennedy M, Nicholson G. Hepatic veno-occlusive disease associated with comfrey ingestion. J Gastroenterol Hepatol . 1990;5(2):211-214.
Review Date: 3/23/2015
Reviewed By: Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.