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Limited evidenceWeight management

Fat Burner Formulas

Across systematic reviews, no over-the-counter fat burner ingredient produces clinically meaningful weight loss, and the category's history is a repeating cycle of an ingredient becoming popular, then being withdrawn after serious harms. What effect exists is almost entirely caffeine's modest appetite and thermogenic action.

What the science says

  • Systematic reviews find no clinically meaningful weight loss Limited evidence

    A systematic review of 315 trials of dietary supplements and alternative therapies for weight loss concluded that few products showed statistically significant weight loss versus placebo, and none met the accepted clinical threshold of at least 2.5 kg more than placebo with acceptable evidence quality. Trials were generally small, short and at high risk of bias.

  • Caffeine is the only ingredient doing consistent work — and it's small Moderate evidence

    Caffeine raises resting energy expenditure by roughly 3-5% and mildly suppresses appetite at 200-400 mg, translating to perhaps 50-100 kcal/day. Tolerance to the thermogenic effect develops within days to weeks, and long-term trials of caffeine alone show weight differences under 1-2 kg.

  • The flagship botanical ingredients have failed replication Limited evidence

    Garcinia cambogia, raspberry ketones, green coffee bean extract, forskolin and CLA all show effects in small industry-funded trials that shrink toward zero in independent, adequately powered studies; the pivotal green coffee bean trial was retracted and its sponsor fined by the FTC. Effects, when present, are typically under 1 kg over 8-12 weeks.

  • Adverse events are the category's most reliable finding Strong evidence

    Weight-loss products account for a disproportionate share of supplement-related emergency department visits — roughly a quarter of an estimated 23,000 US visits per year, concentrated in young adults with cardiac symptoms such as palpitations, chest pain and tachycardia. Weight-loss and bodybuilding supplements are also the leading category in registries of supplement-induced liver injury.

Dosage & safety

Studied doseTypical labels: 150-300 mg caffeine (often as green tea extract or anhydrous), 300-500 mg green tea extract (100-150 mg EGCG), 500-1,000 mg garcinia, 100-200 mg raspberry ketones, 2.5-10 mg yohimbine, 20-50 mg synephrine, 100-300 mcg chromium. Studied doses: caffeine 200-400 mg; green tea catechins 250-500 mg EGCG/day (effect under 1 kg over 12 weeks). No dose of the botanical ingredients has been shown to produce clinically meaningful loss. Any real loss comes from the energy deficit, not the capsule.
SafetyStimulant fat burners raise heart rate and blood pressure and cause insomnia, anxiety and palpitations; combining caffeine with synephrine or yohimbine amplifies this. High-dose green tea extract (over about 800 mg EGCG/day, especially fasted) is an established cause of acute liver injury and has prompted regulatory restrictions in Europe. Usnic acid, once common in fat burners, caused fulminant hepatic failure and liver transplants. Ephedra was banned in the US in 2004; DNP, sibutramine and DMAA continue to appear illegally in products. Contraindicated in cardiovascular disease, arrhythmia, uncontrolled hypertension, pregnancy, and with MAO inhibitors or SSRIs. Yohimbine-containing products are prescription-only in several countries.

How to take it

TimingMorning, if at all — the caffeine dose in a typical serving will ruin sleep taken later in the day.
With food?With food; high-dose green tea extract taken fasted is the pattern linked to acute liver injury.
Worth knowingCount the formula's caffeine against your coffee — most of what people feel is caffeine they could buy for pennies.

Interactions

With medications

  • MAO inhibitors

    Synephrine and yohimbine with an MAOI risk a hypertensive crisis. do not combine

  • SSRIs and other antidepressants

    Yohimbine raises anxiety and blood pressure and interferes with antidepressant therapy. do not combine without your prescriber

  • blood-pressure medication

    Stimulants raise heart rate and blood pressure, directly opposing treatment. avoid if you are treated for hypertension or arrhythmia

  • diabetes medication

    Chromium and green tea catechins can lower glucose modestly on top of treatment. monitor glucose if you use insulin or a sulfonylurea

With other supplements

  • other caffeine-containing supplements or pre-workouts

    Total caffeine adds up fast and drives most of the palpitations and insomnia people report. count total daily caffeine across all products

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Do fat burner supplements work?

Fat burner formulas do not produce clinically meaningful weight loss: a systematic review of 315 trials found no product that met the threshold of at least 2.5 kg more than placebo with acceptable evidence quality (limited evidence). What small effect exists comes almost entirely from caffeine.

Do garcinia, raspberry ketones or green coffee bean help you lose weight?

Garcinia cambogia, raspberry ketones, green coffee bean extract, forskolin and CLA, the flagship fat burner ingredients, show effects in small industry-funded trials that shrink toward zero in independent studies (limited evidence). When present, effects are typically under 1 kg over 8-12 weeks, and the pivotal green coffee bean trial was retracted.

Are fat burners dangerous?

Adverse events are the most reliable finding for fat burner formulas (strong evidence): weight-loss products account for roughly a quarter of an estimated 23,000 US supplement-related emergency visits per year, mostly cardiac symptoms such as palpitations and chest pain. They are also the leading category in registries of supplement-induced liver injury.

How much caffeine is in a fat burner and when should I take it?

Typical fat burner labels contain 150-300 mg caffeine, often from green tea extract, so take it in the morning if at all and count it against your coffee. Take it with food, because high-dose green tea extract taken fasted is the pattern linked to acute liver injury.

Scientific references

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