The first global review of complementary medicines for weight loss in 16 years suggests their use cannot be justified based on current evidence.
Researchers found that while some herbal and dietary supplements resulted in marginal weight loss compared to a placebo, they did not benefit health.They called for more research into their long-term safety.
The sale of diet pills, powders and liquids containing plant or animal products has grown in popularity.
The global industry was estimated to be worth $41bn (£29.3m) last year.
Just 20pc of new products are audited annually to make sure they provide evidence backing their claims.
In some countries, the only requirement is that supplements contain acceptable levels of non-medicinal products.
Unlike pharmaceutical drugs, clinical evidence for their safety and effectiveness is not required before they hit the market, says the review's lead author Erica Bessell from the University of Sydney.(BBC)