Only 6 weight-loss supplements have any evidence behind them, according to a new revie. Here's what they are and whether they're safe.

• Most weight-loss products aren't backed by scientific evidence, according to a new research review.
• Studies supporting the products are flawed or don't show significant benefits, researchers found.
• Six supplements have some evidence, but more research and regulation are needed, the review says.

Most weight-loss supplements on the market are a waste of time and money, new research suggests.

A handful of products, however, have some evidence to support their effectiveness, according to a review published June 23 in the journal Obesity.

Researchers from multiple institutions, including Dartmouth College and the Medical College of Wisconsin, looked at 315 randomized controlled trials of 14 weight-loss supplements. They evaluated the quality of evidence as well as whether the supplements worked for weight loss.

They found that the vast majority of the studies had serious problems, including a small sample size, incomplete data, selective reporting, and lack of blinding for participants.

These findings highlight a need for more rigorous research, the study's coauthors wrote in an accompanying perspective on the study.

Of the 52 reliable studies, only 16 showed significant weight-loss results compared to a placebo. These are the products that might work, and the evidence behind them.

Ephedra and caffeine: An herbal supplement from traditional Chinese medicine, ephedra's active ingredient ephedrine has been shown in some studies to offer a small, short-term boost to weight loss. But while the herb is legal, ephedrine products were banned in the US because evidence emerged of serious risks such as heart palpitations, high blood pressure, vomiting, and insomnia.

Ephedra is often combined with caffeine, which has a wealth of evidence to support its weight-loss and metabolic benefits.

Green tea: There's evidence it can slightly improve weight-loss outcomes in the short term by boosting metabolism and burning fat, in part because it contains caffeine. It also has other significant health benefits, in beverage or extract form, such as improving heart health and lowering cholesterol.

Garcinia: Evidence is mixed on this Indonesian fruit, which is the active ingredient in products like Hydroxycut. It's shown in some studies to boost weight loss, but modest amounts of about two to eight pounds. Other studies have found it isn't more effective than a placebo and that it can cause side effects such as liver damage over time.

Three products were found to have one higher-quality study each that showed significant weight-loss benefits:

Chitosan: A substance extracted from the shells of crustaceans like crabs and lobster. Some research suggests this could help weight loss by binding fats in the digestive system to prevent them from being absorbed. But research is limited and found only a small, short-term effect on weight loss.

Conjugated linoleic acid: A type of omega-6 fatty acid found in meat and dairy. Research suggests this might help reduce fat and build muscle, at least when combined with exercise. But evidence is mixed, and it's not clear that is has benefits as a supplement compared to natural sources like beef, eggs, and mushrooms.

Chromium: This nonessential mineral is found in foods like whole grains, broccoli, and shellfish. In supplement form, it could interact with neurotransmitters like serotonin and might regulate appetite. The researchers found one study showing it improved weight loss by no more than six pounds in a 72-day period. It can also have side effects like dizziness and nausea.