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Weight loss pills

Review of 12 popular weight loss pills and supplements

This is a detailed, evidence-based review of the 12 most popular weight loss pills and supplements on the market today.

This article is based on scientific evidence, written by experts, and fact-checked by experts.
We look at both sides of the argument and strive to be objective, unbiased, and honest.
Last updated on February 24, 2023, and last reviewed by an expert on November 25, 2022. Your Custom Keto Diet →

There are many possible weight loss solutions out there.

Some options are more popular than others, including certain pills, drugs, and natural supplements. These claim to help you lose weight, or at least to make it easier to lose weight, when you combine them with other methods.

They tend to work via one or more of these mechanisms:

It’s important to note that few of these treatments have any scientific basis, and some could have serious health consequences. You should always discuss diet or supplement changes with a doctor or registered dietitian.

To separate the myths from facts, here are the 12 most popular weight loss pills and supplements reviewed by science.

Weight loss pills and supplements

1. Garcinia cambogia extract

Garcinia cambogia became popular worldwide after being featured on “The Dr. Oz Show” in 2012.

It’s a small, green fruit shaped like a pumpkin. The fruit’s skin contains hydroxycitric acid, the active ingredient in garcinia cambogia extract, which is marketed as a diet pill.

How it works

Animal studies show that it can hinder a fat-producing enzyme in the body and increase serotonin levels, potentially helping to reduce cravings.


In one meta-analysis, researchers explored four electronic research databases to investigate the effectiveness of herbal medicines, including garcinia cambogia.

In 54 randomized controlled trials in healthy adults with overweight or obesity, the authors found no difference in weight or body fat percentage between the garcinia cambogia group and the placebo group.

A 2020 review of eight trials on garcinia cambogia found that, on average, it caused weight loss of about 3 pounds (1.34 kg).

Side effects

While it’s widely agreed that garcinia cambogia is safe to take in recommended amounts, studies within the last few years have pointed to some severe side effects.

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A 2018 study documented four cases of women who experienced acute liver failure after taking weight loss supplements containing garcinia cambogia.

Additionally, hepatotoxicity, or liver impairment, and some episodes of mania have also been reported in conjunction with taking garcinia cambogia.

Summary: Even though garcinia cambogia may contribute to modest weight loss, the effects are quite small and may not be noticeable.

2. Hydroxycut

Hydroxycut has been around for more than a decade and is one of the world’s most popular weight loss supplements.

The brand makes several products, but the most common is simply called “Hydroxycut.”

How it works

It contains several ingredients claiming to help with weight loss, including caffeine and a few plant extracts, such as green coffee extract, which we’ll discuss later.


A 2011 meta-analysis of five clinical trials found that supplementation with C. canephora robusta, or green coffee extract, one of the key ingredients in Hydroxycut, led to about a 5.5-pound (2.47-kg) weight loss compared to the placebo.

Side effects

If you are sensitive to caffeine, you may experience anxiety, jitteriness, tremors, nausea, diarrhea, and irritability.

Hydroxycut products were removed from shelves due to cardiovascular risks in 2004 and hepatotoxicity in 2009.

Acute liver injury has also been connected to using Hydroxycut supplements.

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Summary: There are few large-scale studies on this supplement and no data on its long-term effectiveness. More research is needed to determine effectiveness and safety concerns.

3. Green coffee bean extract

Green coffee beans are simply coffee beans that haven’t been roasted.

They contain two substances believed to help with weight loss: caffeine and chlorogenic acid.

How it works

Caffeine can increase fat burning, and chlorogenic acid can slow the breakdown of carbohydrates in the gut.


Several human studies have shown that green coffee bean extract could help people lose weight.

A meta-analysis of all the current randomized control trials on green coffee bean extract’s effect on obesity found that the supplement significantly impacts minimizing body mass index.

Other benefits

Green coffee bean extract may help lower blood sugar levels and reduce blood pressure. It is also high in antioxidants.

Side effects

It can cause the same side effects as caffeine. The chlorogenic acid it contains may also cause diarrhea, and some people may be allergic to green coffee beans.

Summary: Green coffee bean extract may cause modest weight loss, but keep in mind that many studies that have found this have been industry-sponsored.

4. Caffeine

Caffeine is the most commonly consumed psychoactive substance in the world.

It is found naturally in coffee, green tea, and dark chocolate and is added to many processed foods and beverages.

Because caffeine is considered a metabolism booster, companies commonly add it to commercial weight loss supplements.

How it works

One study discussed the effect of caffeine on regulating body weight by increasing energy expenditure — essentially meaning you burn more calories via increased fat breakdown as well as through a process of body heat production called thermogenesis.

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Some studies show that caffeine can cause modest weight loss in humans.

Side effects

In some people, high amounts of caffeine can cause anxiety, insomnia, jitteriness, irritability, nausea, diarrhea, and other symptoms. Caffeine is also addictive and can reduce the quality of your sleep.

There is no need to take a supplement or a pill containing caffeine. The best sources are quality coffee and green tea, which have antioxidants and other health benefits.

Summary: Caffeine could help boost metabolism and enhance fat burning in the short term. However, a tolerance to the effects may develop quickly.

5. Orlistat (Alli)

Orlistat is a pharmaceutical drug sold over the counter under the name Alli and via prescription as Xenical.

How it works

This weight loss pill works by inhibiting the breakdown of fat in your gut, meaning that you take in fewer calories from fat.


A 2003 meta-analysis of studies found that people taking orlistat for 12 months in combination with lifestyle changes saw a 2.9% greater weight reduction than the placebo group.

Other benefits

Orlistat has been shown to reduce blood pressure slightly and may reduce the risk of developing type 2 diabetes when used alongside lifestyle changes.

Side effects

This drug has many digestive side effects, including loose, oily stools; flatulence; and frequent bowel movements that are hard to control. It may also contribute to fat-soluble vitamins such as A, D, E, and K deficiency.

Following a low-fat diet while taking orlistat is often recommended to minimize side effects. Interestingly, a low-carb diet (without medication) has been considered as effective as orlistat and a low-fat diet combined.

Both diets were as effective for weight loss but showed no significant differences in blood sugar and blood lipid levels. However, orlistat combined with a low-fat diet was more effective at lowering blood pressure.

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Summary: Orlistat, also known as Alli or Xenical, can reduce the amount of fat you absorb from food and help you lose weight. It has many side effects, some of which are highly unpleasant.

6. Raspberry ketones

Raspberry ketone is a substance found in raspberries that is responsible for their distinct smell.

A synthetic version of raspberry ketones is sold as a weight loss supplement.

How it works

In isolated fat cells from mice, raspberry ketones increase the breakdown of fat and increase levels of a hormone called adiponectin, which is believed to be related to weight loss.


There are very few studies on raspberry ketones in humans. However, one 2013 study looked at raspberry ketones and some other ingredients and found a potential 2% increase in weight loss over 8 weeks compared with a placebo.

One mouse study using massive doses showed some delay in weight gain.

However, high doses of raspberry ketones were also associated with higher blood sugar levels and higher levels of ALT, a liver enzyme, indicating liver dysfunction.

It’s unknown whether these effects would translate to humans. More research is necessary to determine any benefits and risks.

Side effects

They may cause your burps to smell like raspberries.

Summary: There is no evidence that raspberry ketones cause weight loss in humans and the rat studies that suggest they may work used massive doses. More research is needed.

7. Glucomannan

Glucomannan is a type of fiber found in the elephant yam’s roots, also called konjac.

How it works

Glucomannan absorbs water and becomes gel-like. It “sits” in your gut and promotes a feeling of fullness, helping you eat fewer calories.


One clinical trial showed that taking glucomannan for 60 days could lower body weight among participants with overweight, but only if they were consistently taking the supplement.

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Other benefits

Glucomannan is a fiber that can feed the friendly bacteria in the intestine. It can also lower blood sugar, blood cholesterol, and triglycerides and works effectively against constipation.

Side effects

It can cause bloating, flatulence, and soft stools and can interfere with some oral medications if taken simultaneously.

It is important to take glucomannan with a glass of water about half an hour before meals.

Summary: Studies show that the fiber glucomannan, when combined with a healthy diet, can help people lose weight. It also leads to improvements in various health markers.

8. Meratrim

Meratrim is a relative newcomer to the diet pill market.

It’s a combination of two plant extracts — Sphaeranthus indicus and Garcinia mangostana — that may change the metabolism of fat cells.

How it works

It claims to make it harder for fat cells to multiply, decrease the amount of fat they pick up from the bloodstream, and help them burn stored fat.


Very few studies about Meratrim exist. One study involved 60 people with obesity placed on a strict 2,000-calorie diet and increased physical activity, with either Meratrim or a placebo.

After 8 weeks, the Meratrim group had lost 11 pounds (5.2 kg) and 4.7 inches (11.9 cm) off their waistlines.

Another study suggested that Meratrim had long-lasting effects on appetite suppression.

Side effects

No side effects have been reported.

Summary: One study showed that Meratrim caused weight loss and had several other health benefits. However, the study was industry-sponsored, and more research is needed.

9. Green tea extract

Green tea extract is a popular ingredient in many weight loss supplements. This is because numerous studies have shown that the main antioxidant it contains, EGCG, may aid fat burning.

How it works

Green tea extract is believed to hinder enzymes such as pancreatic lipase, which, when combined with reduced fat absorption, can be an effective way to treat obesity.

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Many human studies have shown that when paired with exercise, green tea extract can increase fat burning and cause fat loss, especially in the belly area.

Side effects

Green tea extract is generally well tolerated. It contains some caffeine and may cause symptoms in people sensitive to caffeine.

All the health benefits of drinking green tea may also apply to green tea extract.

Summary: Green tea and green tea extract could increase fat burning slightly and may help you lose belly fat.

10. Conjugated linoleic acid (CLA)

Conjugated linoleic acid has been a popular fat-loss supplement for years.

It is known as one of the “healthier” trans fats and is found naturally in some fatty animal-derived foods like cheese and butter.

How it works

Conjugated linoleic acid may reduce appetite, boost metabolism, and stimulate the breakdown of body fat.


In a major review of 13 studies, researchers found that conjugated linoleic acid caused weight loss of about 1.1 pounds (0.52 kg) compared with a placebo. This number increased to 2.3 pounds (1.05 kg) in people over 44.

According to another review from 2012, conjugated linoleic acid may make you lose about 1.5 pounds (0.7 kg) compared with a placebo. The authors conclude by questioning the clinical relevance of conjugated linoleic acid’s small effect on body weight.

Side effects

Conjugated linoleic acid can cause various digestive side effects and may have harmful effects over the long term, potentially contributing to fatty liver, insulin resistance, and increased inflammation.

Summary: Conjugated linoleic acid could be an effective weight loss supplement, but it may have harmful effects in the long term. The slight weight loss it may lead to is not worth the risk.

11. Forskolin

Forskolin is an extract from a plant in the mint family that is thought to be effective for weight loss.

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How it works

It may raise levels of a compound inside cells called cAMP, which can stimulate fat burning.


One study of 30 men with excess weight or obesity showed that forskolin reduced body fat and increased muscle mass while not affecting body weight. Another study of 23 women with excess weight found no effects.

Side effects

There is minimal data on the safety of this supplement or the risk of side effects.

Summary: The two small studies on forskolin have shown conflicting results. It’s best to avoid this supplement until more research has been done.

12. Bitter orange/synephrine

A type of orange called bitter orange contains the compound synephrine.

Synephrine is related to ephedrine, which used to be a popular ingredient in various weight loss pill formulations.

However, the FDA has since banned ephedrine as a weight-loss ingredient because of severe side effects.

How it works

Synephrine has similar mechanisms to ephedrine but is less potent. It could help reduce appetite and increase fat burning.


Very few studies have been done on synephrine, but many studies have found that ephedrine can cause significant short-term weight loss.

Side effects

Like ephedrine, synephrine may have serious side effects related to the heart. It may also be addictive.

Summary: Synephrine is a reasonably potent stimulant and is potentially effective for weight loss in the short term. However, the side effects can be severe, so it should be used only with extreme caution and with a doctor’s supervision.

Prescription medications for weight loss

Additionally, some prescription weight loss pills have been somewhat effective.

The most common ones are Contrave and Phentermine.

According to a 2014 review, even prescription weight loss pills don’t work as well as you might assume. On average, they may help you lose 3–9% of your body weight compared with a placebo.

Remember that this is only when these pills are combined with a healthy weight-loss diet. They are ineffective on their own and are not likely a helpful long-term solution to obesity. They also have many possible side effects.

Suggested read: What is caffeine, and is it good or bad for health?


Of the 12 weight loss pills mentioned, the ones backed by the strongest evidence are:

However, many health professionals advise against orlistat because of the unpleasant side effects and against conjugated linoleic acid because of its harmful effects on metabolic health.

That leaves glucomannan, green tea extract, and caffeine. These supplements can be helpful, but the effects are modest at best. And you can find all three naturally in foods and drinks without resorting to a supplement.

Ultimately, no supplement or pill works very well for weight loss. They may give your metabolism a bit of a nudge and help you lose a few pounds, but that’s where their effects likely end.

Determining a healthy weight, focusing on mindful eating, using safe calorie deficits, and increasing your physical activity are still the best ways to lose weight, and these methods work better than all the diet pills combined.

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