Do diet supplements like garcinia actually work?

Short answer

Barely. Garcinia did not beat a fake pill over 12 weeks, and chitosan, glucomannan and CLA added only 1-2 kg, short of the 2.5 kg mark for meaningful loss. Of 22 people with garcinia liver injury, 91% were hospitalized.

Do diet supplements like garcinia actually work?
'Just take it and store less fat' — does this formula hold?
Garcinia is sold as a diet supplement that supposedly blocks the body from making fat. Chitosan, glucomannan and CLA are common too. We checked trials that pitted them against a fake pill to see whether people really lost more weight.
12 weeks of garcinia: the result?
No more weight lost than with a fake pill
135 people on a low-calorie diet took garcinia or a fake pill for 12 weeks. The garcinia group lost 3.2 kg and the fake-pill group 4.1 kg, no difference, and the share of the loss that was fat did not differ either. 42 people finished in each group.
What if you pool the studies?
At most a 0.88 kg difference
An analysis that pooled 9 garcinia studies found a 0.88 kg difference from the fake pill, about 1% of body weight. A 2020 analysis of 54 herbal studies counted 2.5 kg or more as meaningful weight loss and found no effect for garcinia.
What about other popular supplements?
Chitosan 1.84 kg — all 3 under 2 kg
An analysis pooling 67 studies found extra weight loss over the fake pill of 1.84 kg for chitosan, 1.27 kg for glucomannan and 1.08 kg for CLA. None of the 3 reached the 2.5 kg mark for meaningful weight loss. For chitosan, the gap shrank further when only high-quality trials were counted.
What if you pool all 315 studies?
Only 16 of 52 solid studies found a difference
Of 315 randomized trials on diet supplements and alternative therapies, only 52 (16.5%) were solid and had enough data. Of those, 16 (31%) found a difference in body weight, ranging from 0.3 to 4.93 kg.
A bigger problem than the weak effect
22 garcinia liver injuries, 91% hospitalized
Of 1,418 people in a US registry of drug-induced liver injury, 22 were caused by garcinia (5 alone, 16 with green tea). Injury appeared 13-223 days (median 51) after starting, 91% were hospitalized, 1 died and 1 needed a liver transplant.
The diet did the work
The fake-pill group also lost 4.1 kg in 12 weeks
In the garcinia trial, the fake-pill group lost 4.1 kg in 12 weeks on a low-calorie, high-fiber diet alone. Pooling 9 garcinia studies added only 0.88 kg. Most of the weight loss came from the diet.
Bottom line: these supplements barely work
At most 1-2 kg extra; garcinia made no difference
Garcinia did not beat a fake pill over 12 weeks. Chitosan, glucomannan and CLA added only 1-2 kg, short of the 2.5 kg mark for meaningful loss. Of 22 people with garcinia liver injury, 91% were hospitalized. Diet is what drives weight loss.