Early evidence indicates probiotics could be helpful when it comes to weight loss, says Dr. Dariush Mozaffarian, a cardiologist, public health scientist and director of the Food Is Medicine Institute at Tufts University .
One review of research, published in 2025 in Scientific Reports, found that taking probiotic supplements helped overweight and obese people significantly reduce their body weight, waist circumference and body fat. Other trials have linked probiotics to improvements in blood sugar levels.
Some manufacturers are combining probiotics with prebiotics, a type of fiber that feeds gut bacteria. Mozaffarian says he believes those combinations, called synbiotics, are promising.
“It won’t be magical — the pounds won’t melt away — but if you have a healthy microbiome, you may be more likely to be able to lose weight or at least not gain further weight,” he says.
Although few studies have examined the safety of probiotics, they have a long history of safety, particularly in healthy people, according to the NIH.
Side effects: If you have a weakened immune system, rare side effects may occur from taking probiotics. Talk to your health care provider before taking them.
5. Caffeine
Caffeine is a stimulant found in tea, guarana, yerba mate and other herbs that is often added to weight loss supplements. It can give you a jolt of energy, boost your metabolism and increase fat breakdown, Willis says.
“It is an excellent lipolytic agent,” Willis says. “By that I mean it helps liberate fatty acids from our fatty tissues, especially for cardiovascular exercise. It helps to increase fat burning.”
Studies have shown only a moderate weight loss effect, however. The NIH says it “may help you lose a little weight or gain less weight over time.”
Willis says caffeine and other fat-burning supplements need to be accompanied by changes to diet and lifestyle. “If your diet and lifestyle aren’t conducive to losing fat, fix that first,” he says. “It won’t help you if you’ve just eaten three double cheeseburgers with an order of fries and a milkshake.”
Many people experience side effects from caffeine, such as a rise in blood pressure and heart rate, sleep problems, anxiety or jitteriness and gastrointestinal problems. In high doses, caffeine can cause vomiting, heart palpitations and seizures. The NIH recommends no more than 500 mg a day.
Side effects: People with high blood pressure or heart problems should check with their health care provider before taking a supplement with caffeine. Side effects may include headache, insomnia, nervousness, irritability, frequent urination, fast heartbeat and muscle tremors, according to the Mayo Clinic.
6. Green tea extract
Green tea contains a class of phytochemicals that are known as antioxidants, Willis says. Some people believe green tea extract, sometimes called EGCG, contributes to weight loss by boosting energy expenditure and blocking fat absorption.
A few studies do seem to indicate that green tea extracts could make you burn more calories, even when you’re at rest. But there is conflicting research on whether supplements with green tea extracts can help you actually shed pounds, Willis says. If anything, they have only a moderate effect.
Green tea may have other benefits, potentially protecting against heart disease and cancer.
Side effects: Experts warn that large doses could cause liver damage. Signs may include yellowing of the skin or eyes, nausea and stomach pain. Other side effects may include anxiety, tremors, irritability and sleeping problems, according to the University of Rochester Medical Center.
7. Berberine
Berberine is a substance found in plants that has a long history of use in Ayurvedic and traditional Chinese medicine.
The most studied benefit of berberine is its ability to improve insulin resistance in people with diabetes, according to the Cleveland Clinic.
Early research also indicates berberine could help with weight loss. In a recent review of research, published in the International Journal of Obesity, people who took berberine experienced significant drops in their weight and body mass index, compared with those who didn’t take the supplement.
However, the authors note that future studies should focus on reporting standards for the type and amount of berberine consumed, and should have more blind and randomized trials to enhance the reliability of the evidence that berberine can contribute to weight loss.
Side effects: GI symptoms such as nausea, diarrhea, bloating and constipation. Berberine may also interact with prescription medications. As with all supplements, you should talk to your health care provider before taking it.