Castor Oil

Overview

Castor oil is pressed from the seeds of Ricinus communis, a plant known since antiquity for one dominant effect: it makes you go to the bathroom. Swallowed, it is broken down in the gut into ricinoleic acid, which reduces fluid absorption in the small intestine and triggers a strong laxative effect — this is the only use for which regulators have approved it, and the European Medicines Agency classifies it as "well-established use" rather than mere tradition, for short-term relief of occasional constipation (europa.eu). That same purgative action is why midwives have used it for centuries to try to nudge labor along, and two clinical trials looked at exactly that: a Cochrane-style review found limited trial evidence on castor oil, enemas, or baths for cervical ripening¹, and a randomized trial of 81 women past their due date found castor oil did not increase the proportion entering active labor within 24–48 hours compared with sunflower oil, though it was linked to more meconium-stained fluid².

Outside the gut, the evidence thins out fast. A systematic review of hair oils popular in skin-of-color communities found only limited evidence for castor oil's effect on hair growth or quality, unlike coconut oil³. A specially engineered, solvent-based form of castor oil (polyethylated castor oil) is used as a drug-delivery vehicle for the chemotherapy drug paclitaxel — a large trial compared it against a newer nanoparticle formulation, but this tells you about a manufacturing solvent, not about castor oil as a remedy⁴. A commercial castor-oil-containing wound ointment is FDA-registered for topical use on ulcers and burns, though the label does not credit castor oil specifically, only the formulation as a whole (dailymed.nlm.nih.gov). No human evidence in our review supports the popular practice of "castor oil packs" rubbed onto the abdomen for detox, liver support, or fertility.

Dosage

The randomized trial on post-date pregnancies used a single 60 mL dose of castor oil taken by mouth, compared against 60 mL of sunflower oil as control². Regulatory guidance (EMA) approves castor oil as a short-term oral laxative for occasional constipation, not to be taken for longer than one week without medical supervision, though our review does not specify an exact mg or mL dose range for this indication beyond the labor-induction trial figure (europa.eu). For the topical wound-care ointment, the label directs applying a thin film at least twice daily, or as often as necessary (dailymed.nlm.nih.gov). No dosage data in our review support any specific amount for abdominal "castor oil packs" or hair application.

Interactions

Supp.ai, a drug-interaction database, lists 45 documented interactions for castor oil, but the specific drugs and mechanisms are not detailed in our review (supp.ai). The formal safety data reviewed here (EMA, DailyMed) do not describe specific drug interactions beyond the general contraindications listed under safety. No interactions with other herbs are documented in the reviewed studies.

Traditional Use

What biohacking says

Evidence Strength

The strongest evidence here concerns castor oil as an oral laxative — a use recognized by European regulators as "well-established" rather than merely traditional. For labor induction, a systematic review and a dedicated randomized trial both found limited or no meaningful benefit, and one trial flagged a possible downside (more meconium-stained fluid). For hair care, a systematic review found only limited evidence, weaker than for coconut oil. The popular practice of abdominal "castor oil packs" has essentially no human research behind it in our review. Skin application itself is genuinely old — a Korean formulary of 1489 paints it on the navel and soles — but it was done to expel a baby, and the earliest Western record of rubbing it on the belly attributes the effect to the same intestinal mechanism as swallowing.