Summary
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What is CLA?
Conjugated linoleic acid (CLA) is a fatty acid found naturally in milk and meat and produced from safflower and sunflower oils. Various forms or isomers of CLA may perform different functions. CLA supplements are typically made from safflower or sunflower oil (see What It Is). -
Health benefits of CLA:
CLA has been promoted to help with slimming by increasing the ratio of muscle to fat and increasing lean body mass. However, it has not been conclusively shown to reduce overall weight. CLA may lower cholesterol levels. High intake of CLA from certain foods has been linked with decreased risk of colorectal and breast cancer in women, but there is currently no evidence that taking CLA supplements reduces cancer risk (see What It Does). 
What did CL's tests of CLA products find?
Lab tests showed that two products contained less CLA than claimed on their labels: one product contained just 38.5% of the CLA expected, while another was found to contain 85.8% of the CLA claimed on the label. Among products that contained their expected amounts of CLA and were Approved, CL identified one that provided very good quality at the best value (see What CL Found).-
Cost to obtain CLA supplements:
The cost to obtain 3,000 mg of CLA from an Approved product ranged from just 45 cents to more than triple that amount -- over $1.67! -
CLA safety, side effects, and drug interactions:
Nausea and gastrointestinal upset have been reported when taking CLA. CLA supplementation may also worsen blood sugar control, decrease insulin sensitivity, and lower HDL ("good") cholesterol. Liver enlargement and cases of acute hepatitis have also been reported (see Concerns and Cautions).
