No supplement will cause meaningful weight loss on its own, but a handful have enough clinical evidence to suggest they can give a modest edge when combined with a calorie deficit and exercise. The key word is modest: the best-studied options typically produce an extra 1 to 2 kilograms of weight loss over several weeks compared to placebo. Understanding what each one actually does, and how much difference it realistically makes, helps you decide whether any of them are worth your money.
Caffeine and Green Tea Extract
Caffeine is the most widely used metabolic stimulant in the world, and it does increase the rate at which your body burns calories. The catch is that the doses shown to meaningfully boost 24-hour energy expenditure on their own are quite high, in the range of 600 to 1,000 mg per day. That’s roughly six to ten cups of coffee, enough to cause jitteriness, insomnia, and a racing heart in most people.
Green tea extract offers a more practical approach. A study published in The American Journal of Clinical Nutrition found that a green tea extract providing 270 mg of its active compound (EGCG) plus 150 mg of caffeine per day increased 24-hour energy expenditure by about 4% compared to placebo. That 4% translates to roughly 80 extra calories burned per day for someone with an average metabolism. It’s not dramatic, but over weeks it adds up, and the caffeine dose involved is comparable to just one or two cups of coffee.
Glucomannan Fiber
Glucomannan is a water-soluble fiber extracted from the root of the konjac plant. It works by absorbing water in your stomach and expanding into a gel, which slows digestion and helps you feel full on less food. A systematic review and meta-analysis of randomized controlled trials found that glucomannan supplementation led to an average weight loss of about 1 kg more than placebo. In studies lasting eight weeks or less, the effect was slightly larger, around 1.3 kg.
The practical appeal of glucomannan is simplicity: you take it with water before meals, and it reduces the urge to overeat. It won’t reshape your body, but if portion control is your biggest struggle, it can take the edge off hunger without stimulants or side effects beyond occasional bloating. You do need to drink plenty of water with it, since the fiber expands significantly and can cause discomfort or even blockage if taken dry.
Protein Supplements
Protein powder isn’t marketed as a weight loss supplement, but it may be the most useful one. When you cut calories, your body doesn’t just burn fat. It also breaks down muscle, which slows your metabolism and leaves you looking less toned even at a lower weight. Higher protein intake directly counteracts this.
In a 12-week study of obese participants eating 500 fewer calories per day, those supplementing with whey protein lost significantly more fat (3.6 kg versus 2.1 kg) while preserving more lean muscle mass than those on the same calorie deficit without the extra protein. A separate study in physically active military personnel found that consuming two to three times the standard protein recommendation during a steep 40% calorie deficit preserved muscle mass entirely, while a lower protein intake did not. If you’re dieting and exercising, getting enough protein matters more than almost any other supplement on this list. Whey, casein, or plant-based protein powders are all effective ways to hit a higher target when whole food alone falls short.
L-Carnitine
L-carnitine is a compound your body naturally produces to help transport fatty acids into your cells’ energy-burning machinery. The theory behind supplementation is straightforward: more carnitine, more fat burning. The reality is more modest. A dose-response meta-analysis of randomized controlled trials found that L-carnitine supplementation led to an average weight loss of about 1.1 kg compared to control groups. The effect was most apparent when L-carnitine was combined with other lifestyle changes like exercise and dietary adjustments.
L-carnitine is generally well tolerated, though high doses can cause nausea and digestive upset. It’s unlikely to make a noticeable difference if your diet and activity levels stay the same.
Berberine
Berberine is a plant compound that has gained attention for its effects on blood sugar regulation. It activates an enzyme involved in how your cells process glucose and store fat, producing effects that overlap with some diabetes medications. A meta-analysis of randomized controlled trials found that berberine supplementation reduced BMI by about 0.5 points and significantly lowered fasting blood sugar levels.
That BMI reduction is small in absolute terms, but berberine’s real value may be for people whose weight struggles are tied to insulin resistance, blood sugar swings, or intense carbohydrate cravings. By stabilizing blood sugar, it can reduce the cycle of energy crashes and overeating that drives weight gain for some people. Side effects are mostly gastrointestinal: cramping, diarrhea, and nausea, particularly at higher doses. Berberine can also interact with several medications, so it’s worth checking with a pharmacist if you take anything regularly.
Chromium Picolinate
Chromium is a trace mineral involved in insulin signaling, and supplementing with chromium picolinate has been studied specifically for its effect on cravings. Clinical research has found that chromium supplementation can reduce food intake, hunger levels, and fat cravings in overweight women who struggle with carbohydrate cravings. It has also been studied in people with binge eating disorder, where the same craving-reduction mechanism may help break the cycle of compulsive overeating.
Chromium won’t directly burn fat or speed up your metabolism. Its value is narrow but real: if intense carb cravings are the specific barrier between you and a sustainable calorie deficit, chromium picolinate may help quiet them enough to make your diet easier to stick with.
Over-the-Counter Fat Blockers
Orlistat (sold under the brand name Alli at the over-the-counter dose) works differently from everything else on this list. Instead of changing your metabolism or appetite, it blocks your body from absorbing about 25% of the fat you eat. That unabsorbed fat passes through your digestive system and exits in your stool. In clinical trials reviewed by the FDA, orlistat at the OTC dose produced an additional 1.1 to 2.0 kg of weight loss compared to dieting alone.
The trade-off is side effects that many people find intolerable. Because undigested fat has to go somewhere, oily stools, gas, and urgent bowel movements are common, especially after high-fat meals. Some people find this actually reinforces better eating habits, since the consequences of a greasy meal become immediately unpleasant. Others stop taking it within weeks.
Supplements to Be Cautious About
The weight loss supplement market is poorly regulated, and the FDA has repeatedly identified products sold as “natural” supplements that were secretly laced with prescription drugs or controlled substances. Some contained sibutramine, a weight loss drug pulled from the U.S. market in 2010 after it was linked to increased risk of heart attack and stroke. Others contained amphetamine derivatives or powerful diuretics that can cause dangerous drops in blood pressure, seizures, and kidney damage.
These contaminated products are typically sold online with aggressive marketing, dramatic before-and-after photos, and claims that sound too good to be true. A useful rule of thumb: if a supplement promises rapid weight loss without diet or exercise changes, it either doesn’t work or contains something that isn’t listed on the label. Stick with products from established brands that undergo third-party testing, and be skeptical of anything imported from unverified sellers.
Putting It in Perspective
The supplements with the strongest evidence, green tea extract, glucomannan, protein, L-carnitine, and berberine, all produce effects in the range of 1 to 2 extra kilograms lost over weeks to months. That’s real, but it’s a small fraction of what most people are hoping for when they search for weight loss supplements. The calorie deficit you maintain through your diet and the muscle you preserve through exercise will always account for the vast majority of your results.
Where supplements can genuinely help is at the margins: making hunger more manageable, preserving muscle during a cut, stabilizing energy levels, or squeezing out a few extra percentage points of fat burning. Think of them as tools that make a good plan slightly easier to follow, not replacements for the plan itself.