Endaru (Ricinus communis): Castor, the Oil Plant With a Poison in Its Seeds

Endaru (Ricinus communis) grows on every neglected roadside in Sri Lanka, its glossy, star-shaped leaves and spiky red seed capsules recognisable from a moving bus. Village medicine warms its leaves for aching joints and dispenses its oil for a stubborn bowel, and Sri Lankan grandmothers still oil a baby's scalp with it. The same seeds contain ricin, one of the most poisonous substances in nature. Understanding endaru means knowing exactly where the medicine stops and the poison starts.

Botanical and Cultural Background

Castor is a fast-growing shrub of the spurge family, native to East Africa and naturalised across the tropics. Its mottled seeds are about half oil; pressing them yields castor oil, and the pressed cake retains the ricin. Ricin does not pass into properly extracted oil, which is why castor oil has been a household laxative for thousands of years while the raw seed remains dangerous. Ayurveda calls the plant eranda and ranks its oil as the great remedy for vata disorders — stiffness, pain and constipation.

Traditional Uses in Sri Lankan Medicine

• Constipation — a spoon of castor oil, often in warm milk, as a purgative; used sparingly and never habitually.
• Joint pain and swelling — leaves warmed with a little oil and bound over arthritic knees and sprains; castor oil massage for the low back.
• Skin and hair — the oil for cracked heels, minor wounds and dandruff; scalp oiling for infants.
• Root decoction — in classical practice for rheumatism, under a physician's direction.

What the Research Shows

Castor oil's laxative and uterine effects were explained precisely in 2012: its main fatty acid, ricinoleic acid, activates prostaglandin EP3 receptors in the gut and uterus (Tunaru et al., 2012), which also explains its traditional use to induce labour and why pregnant women should avoid it. A 2026 review in Pharmaceuticals catalogued strong laboratory evidence for anti-inflammatory, analgesic, antimicrobial and wound-healing activity in the leaves and oil. Clinical evidence is thinner: castor oil is an accepted, if harsh, stimulant laxative and is used before some medical procedures, and small trials support castor-oil packs for constipation in the elderly. Claims for hair growth and "detox" have no trial support.

Evidence updated September 2026.

How Endaru Is Prepared

Buy cold-pressed, food-grade castor oil; never attempt to press seeds at home. For constipation the traditional adult dose is one to two teaspoons, taken once — it works within hours. For joints, warm a few leaves over a flame, smear with oil and bind over the painful area for an hour. For hair, massage a little warmed oil into the scalp and wash out after an hour.

Safety and Precautions

Never eat castor seeds. A few chewed seeds can kill a child; keep the plant away from play areas. Castor oil is safe externally, but taken by mouth it causes cramping and should not be used regularly, in pregnancy (it induces contractions), in children under twelve, or in anyone with intestinal obstruction or inflammatory bowel disease. Leaf poultices occasionally irritate sensitive skin.