Do These 7 Weight Loss Supplements Actually Work? What Science Says

7 weight loss supplements

Here are some popular weight loss supplements and the science behind each:

1. Chitosan

Chitosan comes from the exoskeleton of shellfish and is used in medicine to reduce bleeding from wounds. Chitosan supplements are promoted as “fat blockers” that can bind with dietary fats so the body doesn’t absorb them, Huntington says.

According to the Obesity review, one well-designed study showed trial participants taking the supplement lost on average about six pounds. A few other higher-quality trials have suggested that chitosan could reduce total cholesterol as well as LDL, or “bad cholesterol.”

However, other studies found no benefit, so more research is needed.

Side effects: Flatulence, bloating, constipation, indigestion, nausea and heartburn.

2. Chromium

Chromium is a trace mineral that plays a role in your body’s metabolism. Chromium supplements are believed to enhance the effects of insulin in the body, and some research shows chromium can improve blood sugar regulation in people with type 2 diabetes.

However, the supplement does not seem to affect blood sugar levels in people without diabetes, according to a research analysis on Examine.com, an independent site that looks at the evidence on nutritional supplements. “Even though chromium is a popular dietary supplement, the research on chromium is fairly mixed, and where benefits have been found, they tend to be small or negligible,” the site’s review says.

Of six studies on the micronutrient in the Obesity meta-analysis, three had a low risk of bias and only one of those linked it to weight loss ranging from 3 to 6 pounds. “If it works, it only helps a little bit,” Huntington says.

Side effects: Stomach pain and bloating. Additionally, there have been a few reports of kidney damage, liver damage, muscular problems and skin reactions following large doses, according to the National Center on Complementary and Integrative Health.

3. Magnesium

Magnesium is an important mineral necessary for many essential bodily functions, says Madesh Muniswamy, a tenured professor in medicine, division of cardiology at the University of Texas Health Science Center at San Antonio. Research suggests as many as half of all Americans don’t get enough magnesium. Magnesium deficiency is more prevalent in people who have obesity, diabetes and metabolic syndrome, and it has been linked to chronic inflammation.

A 2020 systematic review of 32 studies found most adults don’t lose weight when taking a magnesium supplement. However, it did help with weight loss in those with a magnesium deficiency, diabetes, obesity or high blood pressure.

You can find out if you’re magnesium deficient by asking your health care provider to run labs to check your magnesium level.

Side effects: Large doses can cause diarrhea, nausea, abdominal cramping and, in the event of extremely high intake, a risk of death from cardiac arrest. Adults should not consume more than 350 mg per day of magnesium in a supplement, according to the National Institutes of Health (NIH).

4. Probiotics/synbiotics

Probiotics are beneficial bacteria that live in your gut and help break down and digest food. You can get them from supplements or from fermented foods like kefir, sauerkraut and apple cider vinegar.

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.