No weight loss supplement comes close to replacing a calorie deficit through diet and exercise. The ones with the strongest evidence behind them produce modest results at best, typically a few extra pounds lost over several months. That said, a handful of supplements have shown real, measurable effects in clinical trials, and understanding what they can and can’t do will help you spend your money wisely.
Caffeine: The Most Proven Option
Caffeine is the most well-studied metabolism booster available, and it works through a straightforward mechanism: it increases the rate at which your body burns energy at rest. A dose as low as 100 mg (roughly one cup of coffee) raises resting energy expenditure by 3% to 4%. A systematic review and meta-analysis published in the International Journal of Sport Nutrition and Exercise Metabolism confirmed that caffeine increases fat metabolism with a small but consistent effect, and interestingly, higher doses didn’t produce greater benefits than moderate ones. There were also no differences based on fitness level or sex.
The catch is that your body builds tolerance to caffeine over time, which blunts its metabolic effects. Cycling on and off (a few weeks on, a week off) may help preserve the benefit, though this hasn’t been rigorously tested in long-term weight loss trials. Caffeine is cheap, widely available, and safe for most people in moderate amounts, making it one of the more practical options on this list.
Glucomannan: A Fiber That Fills You Up
Glucomannan is a water-soluble fiber extracted from the root of the konjac plant. When it reaches your stomach, it absorbs water and expands into a thick gel, which slows gastric emptying and makes you feel full longer. This gel also reduces how quickly your intestines absorb nutrients, meaning your body processes a meal more gradually.
Multiple randomized controlled trials have shown that glucomannan supplementation leads to weight loss in overweight and obese adults, though results vary quite a bit depending on the dose, study duration, and participant characteristics. The practical takeaway is that it works best as an appetite management tool. You take it with a large glass of water before meals, and it helps you eat less without feeling as hungry. It won’t do much on its own if you’re not also watching your overall calorie intake.
Green Tea Extract: Effective Only at High Doses
Green tea extract contains a concentrated form of catechins, compounds that may boost fat oxidation. But the dose matters enormously. In a randomized, double-blind, placebo-controlled trial of obese women, a daily dose of roughly 857 mg of the active catechin (EGCG) produced significant reductions in body weight, BMI, and waist circumference over 12 weeks. Participants went from an average of 76.8 kg to 75.7 kg.
That’s about 2.4 pounds in three months, which is modest. More importantly, when researchers tested lower doses (302 mg or 360 mg of EGCG daily), there was no meaningful weight loss at all. Most green tea supplements sold over the counter contain far less than 857 mg of EGCG per serving, which likely explains why so many people find them underwhelming. There’s also a safety concern at higher doses: green tea extracts have been linked to liver injury in some cases, particularly in concentrated supplement form rather than brewed tea.
CLA: Small Fat Loss in Women
Conjugated linoleic acid (CLA) is a fatty acid found naturally in meat and dairy. A meta-analysis of eight trials in women found that CLA supplementation over 6 to 16 weeks reduced body weight by an average of 1.2 kg (about 2.6 pounds), with a body fat reduction of 0.76 kg. In overweight and obese women specifically, results were slightly better: 1.29 kg of weight loss and 0.82 kg of fat loss. Post-menopausal women saw the most significant fat reduction at just over 1 kg.
These are real, statistically significant effects, but they’re small enough that you wouldn’t notice them without a scale. CLA is generally well tolerated, though some people experience digestive discomfort. It’s best thought of as a minor addition to an existing weight loss plan rather than a primary strategy.
Alli (Orlistat): The Only FDA-Backed OTC Option
Alli is the over-the-counter version of a prescription fat-blocking medication. It works by preventing your body from absorbing about 25% of the fat you eat, so those calories pass through your digestive system instead of being stored. In clinical studies, people who combined Alli with a calorie-restricted diet and regular exercise lost an average of 5.7 extra pounds over one year compared to people who only dieted and exercised. More than 40% of Alli users in those studies lost at least 5% of their body weight within a year.
The tradeoff is digestive side effects. Because undigested fat has to go somewhere, eating high-fat meals while taking Alli can cause oily stools, gas, and urgent bowel movements. Most people learn quickly to keep their fat intake low, which arguably contributes to the weight loss as much as the pill itself. Alli is the only weight loss supplement that has gone through the rigorous approval process the FDA requires of drugs, which makes it unique in this category.
Supplements That Don’t Live Up to the Hype
Garcinia cambogia is one of the most heavily marketed weight loss supplements, but the evidence is underwhelming. A dose-response meta-analysis of eight trials covering 530 participants found that it reduced body weight by an average of just 1.34 kg (about 3 pounds) compared to placebo. That’s a real but tiny effect, and several of the individual studies showed no benefit at all. Given the cost and the fact that garcinia cambogia supplements have been specifically linked to liver toxicity in case reports, the risk-to-reward ratio is poor.
Chromium picolinate is another popular ingredient, often marketed for its role in insulin function and blood sugar regulation. A systematic review of randomized trials in people with type 2 diabetes found that chromium supplementation did not significantly reduce fat mass overall. Subgroup analysis showed a small effect in people over 55, but the evidence for its benefit in the general population looking to lose weight is inconclusive at best.
Safety Risks You Should Know About
The most important thing to understand about weight loss supplements is how they’re regulated. Under the Dietary Supplement Health and Education Act of 1994, supplement manufacturers are responsible for evaluating the safety of their own products before selling them. The FDA can only take action after a product reaches the market and causes problems. This means supplements don’t go through the same pre-market safety testing that prescription or over-the-counter drugs do.
This regulatory gap has real consequences. The National Institutes of Health maintains a database of supplements linked to liver damage, and weight loss products appear frequently. Specific products that have triggered documented cases of liver injury include Hydroxycut, Herbalife products, OxyELITE Pro, and supplements containing garcinia cambogia. Green tea extracts in concentrated form are also on that list. Beyond liver toxicity, some weight loss supplements have been found to contain undeclared pharmaceutical ingredients, including stimulants and laxatives that don’t appear on the label.
If you do choose to take a supplement, look for products that have been third-party tested by organizations like USP or NSF International, which verify that what’s on the label matches what’s in the bottle. This won’t guarantee effectiveness, but it significantly reduces the risk of contamination or mislabeling.
What Actually Moves the Needle
Even the best-performing supplements on this list produce weight loss measured in single-digit pounds over months. Caffeine gives you a 3% to 4% metabolic bump. Glucomannan helps you eat a bit less. CLA shaves off roughly a kilogram of fat. These effects are real but small, and they only show up consistently when combined with calorie control and physical activity.
The honest answer to “what is a good weight loss supplement” is that no supplement is good enough to be your primary strategy. The ones worth considering are cheap, well-studied, and used as a minor boost on top of the fundamentals: eating fewer calories than you burn, moving your body regularly, sleeping enough, and managing stress. If a supplement promises dramatically more than that, the claim is almost certainly outpacing the evidence.