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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:
- Reducing appetite, making you feel more full so that you eat fewer calories
- Reducing absorption of nutrients such as fat, making you take in fewer calories
- Increasing fat burning, making you burn more calories
It’s important to note that few of these treatments have any basis in science and some could have serious health consequences. You should always discuss any 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.
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.
Effectiveness: In one meta-analysis, researchers explored four electronic research databases to investigate the effectiveness of herbal medicines, including garcinia cambogia.
In a total of 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 that looked at 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 serious side effects.
A 2018 study documented four cases of women who experienced acute liver failure after taking weight loss supplements containing garcinia cambogia (
Even though garcinia cambogia may contribute to modest weight loss, the effects are quite small and may not be noticeable.
Hydroxycut has been around for more than a decade and is one of the most popular weight loss supplements in the world.
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 talk more about later.
Effectiveness: 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 (
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.
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.
A meta-analysis of all the current randomized control trials on green coffee bean extract’s effect on obesity found that the supplement has a significant impact on minimizing body mass index (14).
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 (
Green coffee bean extract may cause modest weight loss, but keep in mind that many of the studies that have found this have been industry-sponsored.
Because caffeine is thought to be 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 (
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 (24).
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.
Effectiveness: 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 (
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 deficiency in fat-soluble vitamins such as vitamins A, D, E, and K (29).
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 (
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 (
Effectiveness: There are very few studies on raspberry ketones in humans, though one 2013 study looked at raspberry ketones along with some other ingredients and found a potential 2% increase in weight loss over 8 weeks when compared with a placebo (31).
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.
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.
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 (
Effectiveness: 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 (
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 at the same time.
It is important to take glucomannan about half an hour before meals, with a glass of water.
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.
Meratrim is a relative newcomer on 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.
Effectiveness: 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 (39).
Side effects: No side effects have been reported.
One study showed that Meratrim caused weight loss and had a number of other health benefits. However, the study was industry-sponsored, and more research is needed.
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 (
Side effects: Green tea extract is generally well tolerated. It does contain some caffeine and may cause symptoms in people who are sensitive to caffeine.
Green tea and green tea extract could increase fat burning slightly and may help you lose belly fat.
CLA has been a popular fat loss supplement for years.
Effectiveness: In a major review of 13 studies, researchers found that CLA 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 age 44 (
According to another review from 2012, CLA may make you lose about 1.5 pounds (0.7 kg) compared with a placebo. The authors conclude by questioning the clinical relevance of CLA’s small effect on body weight (
Side effects: CLA 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.
CLA could be an effective weight loss supplement, but it may have harmful effects in the long term. The small amount of weight loss it may lead to is not worth the risk.
Forskolin is an extract from a plant in the mint family that is thought to be effective for weight loss.
How it works: It may raise levels of a compound inside cells called cAMP, which can stimulate fat burning (
Effectiveness: One study in 30 men with excess weight or obesity showed that forskolin reduced body fat and increased muscle mass while having no effect on body weight. Another study in 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.
The two small studies on forskolin have shown conflicting results. It’s best to avoid this supplement until more research has been done.
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 serious side effects (
How it works: Synephrine has similar mechanisms to ephedrine but is less potent. It could help reduce appetite and increase fat burning (
Effectiveness: 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.
Synephrine is a fairly potent stimulant and is potentially effective for weight loss in the short term. However, the side effects can be serious, so it should be used only with extreme caution and with a doctor’s supervision.
Additionally, some prescription weight loss pills have been somewhat effective.
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 (
Keep in mind 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.
Of the 12 weight loss pills mentioned, the ones backed by the strongest evidence are:
- weight loss: glucomannan, CLA, and orlistat (Alli)
- increased fat burning: caffeine and green tea extract
However, many health professionals advise against orlistat because of the unpleasant side effects and against CLA 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 having to resort 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 weight that’s healthy for you, 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.