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A handful of supplements have randomized trials behind them: caffeine, green tea extract, soluble fiber, and probiotics. In the pooled data, the best of them produce less than a kilogram of extra weight loss compared with placebo, usually over a few weeks to a few months. Most other products sold for weight loss have no meaningful evidence at all. If you want one, psyllium or another soluble fiber has the largest trial base and the fewest risks. This guide covers which is which, how to buy the few worth buying, what can hurt you, and where supplements actually help if you’re on a GLP-1.
What the best trials show
These four have enough trials to pool. Where they show an effect, it’s small.
Viscous fiber (glucomannan, psyllium, guar). Soluble fiber absorbs water and forms a gel in the gut. That slows how fast the stomach empties and adds bulk, which is a plausible route to feeling full sooner. A meta-analysis by Jovanovski and colleagues (American Journal of Clinical Nutrition, 2019) pooled 62 randomized trials with 3,877 participants. Viscous fiber lowered body weight by 0.33 kg compared with control, in trials lasting at least 4 weeks. Glucomannan on its own does no better. A meta-analysis of 9 trials by Onakpoya and colleagues (Journal of the American College of Nutrition, 2014) found no statistically significant weight loss versus placebo.
Probiotics. The idea is that changing gut bacteria changes how energy is harvested from food. A meta-analysis by Borgeraas and colleagues (Obesity Reviews, 2018) pooled 15 trials with 957 adults with overweight or obesity. Probiotics lowered weight by 0.6 kg and BMI by 0.27 compared with placebo. The strains, doses, and durations varied so much across trials that you can’t pick a product from this result.
Green tea and EGCG. Green tea catechins and caffeine together slightly raise energy expenditure in short lab studies. In real-world weight terms, the Cochrane review by Jurgens and colleagues (2012; 18 trials, 1,945 participants) called the weight loss from green tea preparations small, not statistically significant, and not clinically important. That review is the best single summary of the evidence, and it’s unimpressive.
Caffeine. Caffeine is a stimulant that modestly raises heart rate and energy use. A meta-analysis by Tabrizi and colleagues (Critical Reviews in Food Science and Nutrition, 2019) pooled 13 trials with 606 people and found that higher caffeine intake tracked with slightly more weight and fat loss. The trials were small and short. Tolerance to caffeine’s effects develops quickly, and nobody has shown the effect lasts.
So where the effects show up, they’re small. Half a kilogram is about a pound.
Mostly marketing
These show up on labels constantly. None has a pooled body of controlled trials showing weight loss you’d care about, and for several the trials that exist are small, short, or sponsored by the seller:
- Yerba mate
- Caralluma fimbriata
- Fenugreek
- Ginseng
- CoQ10
- Lycopene
- Plant sterols (they lower LDL cholesterol, which is real and useful, but they don’t cause weight loss)
- Garcinia cambogia and raspberry ketones, which are the older generation of the same pitch
The pattern is familiar. A lab or animal study shows something about fat cells, and a label turns it into “burns fat.” A mechanism in a dish is not weight loss in people. When a product claims to boost metabolism or block fat, ask for the human trial, how many people were in it, and how many kilograms they lost. The answer is almost always missing.
Berberine deserves one line because it’s sold as “nature’s Ozempic.” It is not a GLP-1 receptor agonist, and it has no trial showing weight loss anywhere near what semaglutide or tirzepatide produce.
Fixing a deficiency is a different thing
B12, iron, and vitamin D appear on weight-loss lists because low levels cause fatigue. If you’re deficient, correcting it makes you feel better and function normally. That can make exercise easier. It does not burn fat, and taking more when your level is already normal does nothing for weight.
Vitamin D is a common trap. Blood levels run lower in people with obesity, in part because the vitamin is fat-soluble and gets distributed into a larger fat mass. The low level is partly a result of the weight, not a cause of it. If a test your clinician orders shows it’s low, correcting it is worthwhile, but don’t expect the scale to move. Biotin and magnesium are often listed too, and they have no weight-loss evidence either.
How supplement regulation works
Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), supplements don’t need FDA approval before they go on sale. The manufacturer doesn’t have to show the FDA that the product works, or submit safety data for most ingredients, before selling it. The FDA generally acts only after a product is on the market, and the burden is on the FDA to show it’s unsafe. That’s how ephedra stayed on shelves until the FDA banned it in 2004.
Labels can make “structure/function” claims like “supports metabolism” as long as they carry the line “This statement has not been evaluated by the Food and Drug Administration.” That sentence is the tell that nobody checked.
Drugs work the other way. A prescription weight-loss drug has to show efficacy and safety in large randomized trials before approval. Even over the counter, the only FDA-approved weight-loss product is orlistat 60 mg (Alli), and it’s regulated as a drug, not a supplement.
One more distinction matters on this site. Compounded semaglutide and tirzepatide are prescription medications prepared by licensed pharmacies, but compounded preparations are not FDA-approved and have no trials of their own. The trial results below come from the brand-name drugs.
How to choose a product, if you buy one
- Look for a third-party seal. USP Verified or NSF Certified means an independent lab checked that the bottle contains what the label says, at the stated dose, without listed contaminants. It says nothing about whether the product works.
- Skip proprietary blends. If the label lists a “blend” with one total weight, you can’t know how much of anything you’re taking.
- Read the caffeine. Many products don’t state total caffeine clearly, or stack several sources (guarana, green coffee, yerba mate, kola nut) on top of each other.
- Distrust the fastest promises. “Lose 10 pounds in 2 weeks” is the most reliable sign of a product to avoid. Weight loss that fast, when it happens, is mostly water.
- Check the FDA’s tainted-products list. The FDA has repeatedly found weight-loss “supplements” spiked with undeclared prescription drugs, including sibutramine, which was withdrawn from the US market over cardiovascular risk.
Where supplements cause harm
Natural does not mean safe. A few specific risks are well documented.
Liver injury from green tea extract. Concentrated extract is a very different exposure from drinking tea. The European Food Safety Authority (2018) found that EGCG doses of 800 mg a day or more from supplements were linked to raised liver enzymes in trials. In the US Drug-Induced Liver Injury Network, the share of liver injury cases caused by herbal and dietary supplements rose from 7% to 20% between 2004 and 2014 (Navarro et al., Hepatology 2017), with multi-ingredient weight-loss and bodybuilding products prominent among them.
Stimulant blends. Stacked stimulants raise heart rate and blood pressure. Geller and colleagues (NEJM, 2015) estimated about 23,000 US emergency visits a year from dietary supplements, and weight-loss and energy products were involved in 71.8% of the visits for palpitations, chest pain, or fast heart rate. If you have high blood pressure, a heart rhythm problem, or anxiety, or you take stimulant medication, talk to your clinician before taking anything with added caffeine.
Interactions. Supplements interact with prescription drugs, and people rarely mention them at appointments. Tell your prescriber about everything you take, especially if you’re on blood thinners, blood pressure or diabetes medication, or anything for seizures or mood. Pregnancy and breastfeeding are a reason to stop weight-loss supplements entirely and ask first.
Choking on glucomannan. Glucomannan swells to many times its size in water. Taken as a tablet or capsule without enough fluid, it can expand in the throat or esophagus and cause a blockage. Take any bulk-forming fiber with a full glass of water, and don’t take it right before lying down. People with trouble swallowing should avoid it.
How the numbers compare with a GLP-1
In STEP 1 (Wilding et al., NEJM 2021; 1,961 adults), brand-name semaglutide 2.4 mg (Wegovy) produced 14.9% average weight loss at 68 weeks, compared with 2.4% on placebo. In SURMOUNT-1 (Jastreboff et al., NEJM 2022; 2,539 adults), brand-name tirzepatide (Zepbound) produced up to 20.9% at the 15 mg dose over 72 weeks, compared with 3.1% on placebo.
The supplement numbers above are already net of placebo, so compare like with like. For a 100 kg person, the drug minus placebo works out to roughly 12.5 kg (Wegovy) to 17.8 kg (Zepbound 15 mg). The best pooled supplement results are 0.3 to 0.6 kg. That is a gap of more than twentyfold in effect size, and the drug trials ran more than a year in thousands of people.
Plenty of people don’t need or qualify for medication, and that’s fine. But paying for a fat burner and expecting a result is a bad bet. If you want to know whether you’re a candidate for a GLP-1, the GLP-1 guide covers who qualifies and what treatment involves.
Supplements that make sense alongside a GLP-1
Here supplements can earn a role for some people, because they can help with problems the medication may cause. Not everyone needs them, so check with your clinician first.
- Fiber for constipation. GLP-1s slow gut movement, and smaller meals mean less fiber and fluid. If you get constipated, psyllium taken with plenty of water is one option to ask your clinician about. The full approach is in GLP-1 constipation.
- Protein powder. Appetite drops, and protein is the first thing to fall short. If you struggle to eat enough protein, a plain whey or plant protein shake is food in a convenient form. It can help you reach your target. A range often cited is 1.2 to 1.6 g of protein per kilogram of body weight a day, and your clinician can set yours. That target comes from muscle research in dieters, not from GLP-1 trials. The numbers are in protein targets on a GLP-1.
- Creatine. Part of GLP-1 weight loss is lean mass. Resistance training is what protects muscle. Creatine monohydrate is the supplement with the most trial evidence for adding to strength gains from that training, though it hasn’t been tested specifically in GLP-1 users. Dosing and the water-weight effect are in does creatine help with weight loss?.
What actually drives weight loss
No supplement replaces diet, activity, and sleep. A calorie deficit you can sustain, protein at every meal, regular strength training, and enough sleep do more than every product on this page combined. When those aren’t enough, prescription medication is the next tool with evidence behind it.
The question worth a trial is whether any supplement helps people keep weight off after stopping a GLP-1, when appetite comes back. In SURMOUNT-4 (Aronne et al., JAMA 2024), people who stopped brand-name tirzepatide (Zepbound) regained about 14% of body weight over the next year. Fiber and protein are plausible ways to blunt that, and we don’t know whether they do, because nobody has tested them.
