Castor oil does have anti-inflammatory properties, and there’s a clear biological explanation for why. About 85% to 95% of the fatty acids in castor oil consist of ricinoleic acid, a unique compound that interacts with the body’s inflammation signaling pathways. While the research base is still limited compared to conventional anti-inflammatory drugs, the evidence that does exist supports its use for certain types of inflammatory pain.
How Ricinoleic Acid Reduces Inflammation
Ricinoleic acid is the active ingredient behind castor oil’s anti-inflammatory effects. When researchers systematically deactivated hundreds of cell receptors to figure out how ricinoleic acid works, they identified a specific target: the EP3 prostanoid receptor. This receptor belongs to a large family of cell-surface receptors involved in transmitting chemical signals, including signals related to pain and inflammation.
Prostanoid receptors are part of the same system that conventional anti-inflammatory drugs like ibuprofen target. The difference is in approach. Standard painkillers typically block the production of inflammatory molecules called prostaglandins. Ricinoleic acid instead binds directly to the EP3 receptor, which modulates how inflammation signals are processed in tissue. This interaction is what gives castor oil both its analgesic (pain-reducing) and anti-inflammatory effects.
What the Clinical Evidence Shows
The most notable clinical study on castor oil and inflammation compared it head-to-head with diclofenac sodium, a widely prescribed anti-inflammatory drug, in patients with knee osteoarthritis. In this randomized, double-blind trial published in Phytotherapy Research, 100 patients were split into two groups: one took castor oil capsules three times daily, the other took 50 mg of diclofenac three times daily, both for four weeks.
After the treatment period, both groups showed statistically significant improvements in osteoarthritis symptoms. The castor oil group reported no adverse effects, while the diclofenac group had a notably higher rate of side effects. The researchers concluded that castor oil could serve as an effective therapy for primary knee osteoarthritis. That’s a meaningful finding, because diclofenac is one of the strongest over-the-counter anti-inflammatory medications available in many countries.
It’s worth noting this was a single study with 50 patients per group. The results are promising but haven’t been replicated at scale. Most of the traditional uses of castor oil for inflammation, including headache relief, menstrual cramps, and wound healing, lack rigorous clinical trials to confirm effectiveness.
Topical vs. Oral Use
Castor oil is used both on the skin and taken by mouth, but these routes work differently. When applied topically, ricinoleic acid can help reduce localized swelling and pain at the site of application. This is the most common way people use it for joint stiffness or muscle soreness, often by massaging the oil into the skin or applying a castor oil pack (a cloth soaked in the oil and placed over the affected area).
Oral castor oil has a more complex story. The only use approved by the FDA is as a laxative for temporary constipation. When swallowed, ricinoleic acid is released from the oil in the intestine, where it activates EP3 receptors on intestinal and uterine muscle cells. This stimulates intestinal movement, which is what produces the laxative effect. Whether oral castor oil provides meaningful systemic anti-inflammatory benefits throughout the body remains an open question. The osteoarthritis trial used oral capsules and found positive results, but routine oral use of castor oil comes with digestive side effects like cramping and diarrhea that make it impractical as a daily anti-inflammatory.
Safety and Skin Reactions
Topical castor oil is well tolerated by the vast majority of people. One dermatology department that routinely patch-tests castor oil on roughly 400 patients per year as part of its cosmetic allergy screening reports that the overwhelming majority show no allergic or irritant reactions. Cases of allergic contact dermatitis from castor oil or its derivatives have been documented, but they’re rare.
If you’re using castor oil on your skin for the first time, testing a small amount on your inner forearm and waiting 24 hours is a simple way to check for sensitivity. For oral use, the laxative effect is the main concern. Even small amounts can trigger intestinal cramping, so taking it by mouth purely for anti-inflammatory purposes requires weighing that tradeoff.
How It Compares to Standard Options
Castor oil is not a replacement for conventional anti-inflammatory medications when you need reliable, fast-acting pain relief. NSAIDs like ibuprofen and naproxen have decades of large-scale clinical data behind them and predictable dosing. Castor oil has a single comparative trial showing it can match diclofenac for knee osteoarthritis over four weeks, which is encouraging but not the same level of evidence.
Where castor oil may have an advantage is in its side effect profile. Long-term NSAID use is associated with stomach ulcers, kidney strain, and cardiovascular risks. The osteoarthritis trial reported zero adverse effects in the castor oil group. For people who experience stomach problems with conventional painkillers or who prefer a plant-based option for mild to moderate inflammatory discomfort, topical castor oil is a reasonable choice to try. It works best for localized issues like sore joints, stiff muscles, or minor swelling where you can apply it directly to the area.