Researchers in the Netherlands have found fish oil supplements, and even certain fish, may make chemotherapy less effective. They first noted chemotherapy drugs, such as, cisplatin would become less effective in the presence of fish oil. They then assessed whether the average levels in the body of someone taking fish oil supplements would be enough to cause this effect if having chemo treatment. They looked at fish oil use among 118 cancer patients undergoing chemotherapy. The researchers also assessed the levels of fatty acid in 50 healthy volunteers after they consumed either fish or fish oil supplements to asses their risk of chemotherapy becoming hindered due to the presence of fish oil. They concluded, until further data become available, fish oil may best be avoided on the days surrounding chemotherapy. Published online April 2 in JAMA Oncology.