I've not taken it, and I don't know anyone that has. However, I found the following info which may be helpful.
According to Dr. Weil:
The current excitement about CLA stems from studies suggesting it may have powerful health benefits including the ability to strengthen the immune system, protect against certain types of cancer, promote cardiovascular health, and reduce body fat.
All of the supposed benefits associated with CLA are based on the results of animal studies. However, a recently completed study by the Agricultural Research Service, an arm of the US Department of Agriculture, found no significant, positive benefits when CLA supplements were tested in women over a three-month period.
Discussing the results, the researchers reported the women ate familiar everyday foods at mealtimes and for an evening snack, but before each meal took capsules containing sunflower oil as a control. For the second and third months of the study, 10 volunteers took 3.9 grams of CLA in capsules daily.
The researchers found no significant changes in more than a dozen indicators of immune system activity, no reduction in body fat, and no increase in muscle mass. And they saw no lasting changes in levels of leptin, a hormone linked to appetite control. (The researchers did find temporary decreases in leptin levels, which would have the effect of boosting, not reducing, appetite.) In addition, no changes were seen in blood fats, which are risk factors for heart disease.
The researchers noted that the amount of CLA used was comparable to levels given to animals in studies that had found health benefits. If you’re considering CLA for weight loss, you should also be aware of the results of a Swedish study reported in December 2000: After taking CLA for 64 days, participants experienced a reduction in body fat, although none lost weight. Many participants complained of nausea and had difficulty taking the required 12 capsules of CLA daily.
I don't normally quote Dr. Weil. Oddly, I can't find references it to this supplement in any of the usual places I check, such as the Mayo Clinic site, Intelihealth, WebMD, and other health sites that are considered reputable.
I did find something quoted in an article by the BEEF industry, as they were trying to promote the health benefits of beef (apprently CLA is found naturally in meat and dairy products, although in tiny quantities) They said:
In the latest study, 53 men and women were randomly assigned to either a CLA-treated group (Natural, Inc.'s Tonalin® CLA) or to a control group that received olive oil capsules. The CLA group experienced body fat reductions of 3.8% over the 14-week trial. Additional human studies on the body fat reduction aspects of CLA are anticipated in the next six months
I may be too cynical to comment on something like this. But this is what I'm curious about.... The control group reduced fat by 3.8% over 14 weeks. I'm assuming this was not in addition to any weight loss program. You can reduce your weight by more than that percentage with a diet and exercise program. If you took the CLA at the same time, it seems to me that the additional fat loss (if any) would be very small and negligable.
Most of the references I found stated that it's just too soon too tell with CLA, due to the lack of human research so far.
So the jury is still out. If you decide to try this, please keep us updated on your progress