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Instant Knockout Fat Burner Review: Is It Safe and Effective?

By Markita Lewis, MS, RD

Medically Reviewed by Anthony Dugarte, MD

Last Updated on July 13, 2021

Dietitian Rating:


About This Rating
The average rating of this product is calculated based on the evaluation of the following factors:
  • Support for Claims:4.7
  • Ingredient Safety:4.0
  • Value for the Price:4.0
  • Brand Transparency:3.0

Instant Knockout is a fat-burning supplement made for professional MMA fighters and boxers but is useful for any active adult looking to get leaner. Many of its ingredients are backed by research to help support your metabolism, so this supplement may be worth its price.

Written by
Markita Lewis, MS, RD
Registered Dietitian Nutritionist
Markita Lewis is a registered dietitian with over 5 years of experience in the field of nutrition and health. Prior to her professional career, Markita completed a combined masters and dietetic internship program at the University of Georgia. She obtained her undergraduate degree at Louisiana State University in Nutrition and Foods Sciences, concentrating in dietetics with a minor in Psychology.
Medically Reviewed by
Anthony Dugarte, MD
Medical Reviewer
Anthony Dugarte, M.D., C.S.C.S. is a health and wellness writer and medical content reviewer. In addition to dedicating the last 7 years to medical research, Dr. Dugarte also has more than a decade of experience in strength and conditioning, nutrition, and rehabilitative exercise, as well as authoring and reviewing health and wellness-related content.

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Instant Knockout Fat Burner Review: Is It Safe and Effective?


  • Contains several vitamins and minerals to support health
  • Transparency about concentration of ingredients in supplement


  • Not all ingredients show consistent results in human research
  • Return policy is very strict
  • Multiple caffeine containing ingredients increase risk for caffeine toxicity

What Is Instant Knockout?

Instant Knockout is a fat-burning supplement developed with professional MMA fighters and boxers in mind.

Even if you’re not a professional fighter, Instant Knockout claims that it can help active men and women kickstart their metabolism and improve their body composition.

This supplement is claimed to help individuals speed up weight loss by boosting their body’s natural metabolic rate, reduce hunger cravings, and fuel energy levels.

A daily dose of Instant Knockout is 4 capsules spread throughout the day. It’s recommended to take one capsule first thing in the morning, one before lunchtime, one in the afternoon, and the last before the evening meal.

Instant Knockout is one of the premium sports supplements formulated by Roar Ambition.

Evaluation of Ingredients

Green Tea Extract, 500 mg

Green tea extract contains caffeine and catechins (a type of polyphenol antioxidant) to aid with energy expenditure and weight loss. (1)

Green tea has nearly twice the concentration of catechins as black tea.

In a 2017 review, green tea extract supplementation was found to increase brown fat activity and help increase energy expenditure through the activity of both caffeine and catechins. (1)

The caffeine and catechins work together synergistically to increase norepinephrine activity and promote fat oxidation and weight loss.

Summary: Green tea extract contains caffeine and catechins, which work together to promote energy burning, fat oxidation, and weight loss.

Cayenne Pepper Seeds, 100 mg

Cayenne and chili peppers contain antioxidants, vitamins, and capsaicin that help with weight loss. (2)

Capsaicin is known to activate the sympathetic nervous system (which helps regulate the metabolism), increase energy expenditure and diet-induced thermogenesis, decrease energy intake, and improve satiety.

Capsaicin can even reduce cravings for salty, sweet, or fatty foods.

Summary: Cayenne pepper sides contain capsaicin which may help regulate metabolism, increase energy expenditure and thermogenesis, decrease energy intake, improve satiety, and reduce food cravings.

Glucomannan, 1,800 mg

Glucomannan is a water-soluble fiber from the tuber or root of the elephant yam, a tropical plant primarily grown in South and Southeast Asia, the Pacific Islands, and Africa.

It is marketed as a weight-loss supplement, but the research is inconsistent in showing that glucomannan can reduce body weight over time. (3)

Summary: Glucomannan does not have a consistent effect in showing efficacy as a weight-loss supplement.

Caffeine Anhydrous, 300 mg

Caffeine anhydrous is a concentrated powder made from the dehydration of caffeine-containing plants and is shown to help reduce weight, fat mass, and BMI. (4)

If caffeine anhydrous is taken before a meal (approximately 0.5–4 hours before), it may help suppress appetite. (5)

Caffeine is known to improve mood and cognition and can decrease perceived exertion and pain during workouts. (6)

These things together can help improve exercise performance. (7)

Summary: Caffeine anhydrous may help improve exercise performance, mood, and cognition and suppress appetite.

Vitamin B6, 5 mg, 250% DV

Vitamin B6 is a water-soluble vitamin that helps to regulate metabolism in the body. (8)

In metabolism, it is necessary for the biosynthesis of amino acids and the metabolism of other nutrients. (9)

Summary: Vitamin B6 is necessary for amino acid synthesis and metabolism regulation.

Vitamin B12, 10 mcg, 166% DV

This supplement contains vitamin B12 as cyanocobalamin, another water-soluble vitamin. (10)

It is necessary for carbohydrate and fat metabolism within the cell and is also required for the metabolism of some amino acids. (11)

Summary: Vitamin B12 is needed for the metabolism of carbohydrates, fats, and some amino acids.

GTF Chromium, 100 mcg, 82% DV

Chromium is an essential trace mineral and is the biologically active component of the glucose tolerance factor (GTF), which enhances the action of insulin in the body.

Animal studies find a relationship between supplementation with GTF extracted from yeast and improvements in weight, body composition, and insulin sensitivity.

Human studies find chromium supplementation may have a medium effect on weight loss and decreased body fat percentage in overweight and obese individuals, but more research needs to be done to see the utility of chromium as a weight loss agent. (12)

Summary: GTF Chromium is a trace mineral that may have a medium effect in assisting with weight loss and decreasing body fat in overweight and obese individuals.

Zinc, 10mcg, 150% DV

Zinc is a mineral important for metabolism, endocrine function, and the production of testosterone to promote muscle growth and strength. (13)

A study found that intake of a supplement containing zinc and magnesium increased Insulin-like Growth Factor-1 (IGF-1), which increased serum testosterone. (14)

Summary: Zinc is required to produce testosterone, and limited research suggests that a multivitamin supplement containing zinc helped increase testosterone.

Shop Instant Knockout
Instant Knockout uses research-backed ingredients relevant to weight loss, which may be a good option to add to your existing exercise and healthy nutrition routine.
One Bottle / 120 Capsules: $50.00

Piperine, 10 mg

Piperine is an alkaloid that comes from black pepper extract. Studies find that piperine can inhibit the creation of new fat cells. (15)

One animal study found that obese rats on high-fat diets and dyslipidemia (an abnormal level of cholesterol) had decreased body fat mass and blood lipids when taking piperine. (16)

Summary: Piperine may help reduce the creation of fat cells, and in animals, decreased body fat mass and blood lipids.

Green Coffee Bean, 100 mg

Green coffee bean extract comes from coffee beans that haven’t been roasted and contain higher levels of chlorogenic acid (a polyphenol and antioxidant) compared to roasted coffee.

A meta-analysis of trials found that supplementation with green coffee bean extract for more than 4 weeks significantly reduced BMI and body weight, with greater effects in individuals with BMI over 25kg/m². (17)

Summary: Green coffee bean extract can help reduce BMI and body weight in individuals.

Verdict on Claimed Benefits

Below is our summary of the available evidence for the claimed benefits of Instant Knockout based on the available research:

Boosts your body’s natural metabolic rateStrong Evidence
Reduces hunger cravingsGold Star Evidence
Fuels energy levelsGold Star Evidence

Side Effects, Safety, and Dosage

The max dosage for Instant Knockout is 4 capsules per day.

The dosage is spread throughout the day. You take one capsule first thing in the morning, one before lunchtime, one in the afternoon, and the last before the evening meal.

If you take your last dose of Instant Knockout too late at night, it could interfere with getting adequate sleep – a side effect of most stimulants.

It’s recommended to have at least 5 hours between your last dose and when you go to bed.

Instant Knockout contains green coffee bean extract, green tea extract, and caffeine anhydrous, which are all sources of caffeine.

Caffeine anhydrous is a highly concentrated form of stimulant. You may react differently to it than to natural forms of caffeine. This can be especially dangerous if you have a history of heart conditions.

The FDA recommends limiting caffeine intake to no more than 400 mg daily (an equivalent to 3 or 4 cups of coffee). Because this supplement contains multiple forms of caffeine, it may be easy to exceed this limit. (18)

Excess caffeine can lead to restlessness, nausea, agitation, rapid heart rate, and elevated blood pressure.

Rapid intake of caffeine of over 1,000 mg or higher has been associated with seizures and even death. (19)

Because Instant Knockout contains multiple stimulants, do not take this supplement with other products that contain stimulants or caffeine, such as coffee or tea, as this may cause you to have an unsafe intake of caffeine.

Glucomannan has been associated with side effects like increased belching, bloating, stomach fullness, and diarrhea. (20)

This supplement is recommended only for adults ages 18+. Do not take this supplement if you are pregnant or nursing.

Be sure to consult a health professional before using this supplement, especially you have any medical conditions or are currently taking medications.

Cost and Where to Buy

Instant Knockout Fat Burner is available in a few bundles from the Instant Knockout website:

  • A one-month supply (1 bottle) costs $59 plus the cost of shipping.
  • A two-month supply (2 bottles) costs $118 and has free delivery in the USA and UK.
  • The Ultimate Shredding Stack (3 bottles) costs $185 and includes one free bottle, free worldwide delivery.

Returns are only available for unopened and unused products and have to be done within 30 days of receipt in the US and only after 14 days of receipt in the UK and the rest of the world.

This strict return policy does pose a risk for you to invest a lot of money upfront for a product that you may not like without the chance for a trial period.

The cost of this fat-burning supplement is on par with other capsule fat burners on the market.

How It Compares

I found it refreshing to see that Instant Knockout was upfront about the concentrations of ingredients it uses.

Some other popular brands, such as Skald, will have a proprietary blend of ingredients, and it is difficult to determine if the ingredients are in significant amounts to actually work.

The recommended daily dosage for Instant Knockout is four capsules per day.

Other competitors provide a fat-boosting formula requiring fewer pills per day, which may be more convenient to remember.

However, with fewer pills, the concentration of active ingredients may be limited.

Instant Knockout provides detailed Supplement Facts information instead of a proprietary blend compared to other thermogenic supplements, but the pill burden may not be feasible for some.

The Bottom Line

Instant Knockout appears to be a promising fat-burning supplement that does not include ingredients irrelevant to fat loss and metabolism.

Most of the ingredients in this product are backed by solid research, making me feel more certain about its efficacy.

This could be a safe fat-burning supplement to incorporate into your wellness journey if you are active and looking for faster weight loss.

Still, it is best to check with your doctor before starting a supplement (especially if you may be sensitive to stimulants).

A Word from Our RD

I regularly speak with clients who desire to lose weight, and I notice the same trends: they need to work on exercise and changing their diet.

A diet focused on lean protein, fruits and vegetables, moderate portions of whole grains, and healthy fats can help support your metabolism and weight by providing the nutrients you need for your body to function well.

For some of my clients who have made dietary changes and still find weight loss challenging, one of the culprits is lack of exercise.

Incorporating regular strength-building and cardio exercise for 150–300+ minutes per week is needed for improved fat and weight loss.

The most important thing to remember is that fat-burning and changing your body composition cannot happen with a supplement alone.

I recommend turning to lifestyle changes before expecting a pill to change things without any effort on your part.

Shop Instant Knockout
Instant Knockout uses research-backed ingredients relevant to weight loss, which may be a good option to add to your existing exercise and healthy nutrition routine.
One Bottle / 120 Capsules: $50.00
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  1. A minireview of effects of green tea on energy expenditure:
  2. Chili pepper as a body weight-loss food:
  3. The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials - PubMed:
  4. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials:
  5. Caffeine, coffee, and appetite control: a review:
  6. Caffeine: cognitive and physical performance enhancer or psychoactive drug?:
  7. Acute caffeine ingestion enhances strength performance and reduces perceived exertion and muscle pain perception during resistance exercise:
  8. Vitamin B6:
  9. Vitamin B6 and Its Role in Cell Metabolism and Physiology:
  10. Vitamin B12:
  11. Vitamin B12:
  12. A meta-analysis of the effect of chromium supplementation on anthropometric indices of subjects with overweight or obesity:
  13. The many faces of testosterone:
  14. Effects of a Novel Zinc-Magnesium Formulation on Hormones and Strength:
  15. Piperine, a Component of Black Pepper, Inhibits Adipogenesis by Antagonizing PPARγ Activity in 3T3-L1 Cells:
  16. Effect of piperine in the regulation of obesity-induced dyslipidemia in high-fat diet rats:
  17. The effect of green-coffee extract supplementation on obesity: A systematic review and dose-response meta-analysis of randomized controlled trials:
  18. Spilling the Beans: How Much Caffeine is Too Much?:
  19. The clinical toxicology of caffeine: A review and case study:
  20. Safety and Efficacy of Glucomannan for Weight Loss in Overweight and Moderately Obese Adults: