Like a number of other carrier oils, castor oil has developed several credentials as a useful massage treatment for sore muscles and inflammation. It is particularly effective against joint pain and has even been viewed as a natural arthritis treatment by some holistic sources. This is due to the oil's strong anti-inflammatory qualities as well as the analgesic effects found in ricinoleic acid. A 2009 study observed the effects of castor oil on severe cases of knee pain, and found that its benefits equated to those of conventional pain-relief treatments.