The promise of fast weight loss is hard to resist. But do weight-loss supplements lighten anything but
your wallet? And are they safe?
What are dietary supplements?
Dietary supplements are sold as health aids. They’re taken by mouth. Common ingredients are vitamins,
minerals, fiber, caffeine, herbs and other plants. The global market for weight loss products and services
hit $254.9 billion in 2021, and it’s estimated to reach $377.3 billion by 2026.
Some of the most popular supplements claim to improve nutrition, boost energy, build muscle or burn
bodyfat. Dietary supplements are not medicines. They aren’t meant to treat or cure disease.
How do weight loss supplements work?
Reducing appetite, making you feel fuller 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.
How are dietary supplements regulated?
Companies that make supplements are responsible for the safety of their products. They must ensure
that their products are free of contaminants and that they’re accurately labeled.
Dietary supplements don’t require approval by the U.S. Food and Drug Administration (FDA). But if a
supplement is found to be unsafe, the FDA can issue warnings or ask that it be withdrawn from the
The FDA can also act against companies that make false or unsupported claims to sell their supplements.
Interpreting claims about weight loss
A 2021 review of dietary supplements found that out of over 300 studies, only 16 had sufficient
evidence to “prove” significant weight loss. Most of the studies’ results were unreliable due to factors
like bias and short duration. Makers of dietary supplements rarely carry out clinical trials due to the
significant cost and time that are required, not to mention that the trials will likely NOT support their
claims. This is the reason why there’s little scientific evidence to show that weight-loss supplements
Example – Raspberry Ketones
This supplement is marketed as a “clinically proven” weight-loss product. That claim is supported by
ONE clinical trial.
The trial included 70 adults with obesity. All were placed on a restricted diet and exercise program. They
were then randomly assigned to receive either a placebo or a supplement containing raspberry ketone,
caffeine, bitter orange, ginger and garlic root extract.
The 45 people who completed the trial all lost weight:
The average weight loss in the supplement group was 4.2 pounds (1.9 kilograms).
The average weight loss in the placebo group was 0.9 pounds (0.4 kilograms).
While these results are intriguing, the fact that the trial was small and lasted only eight weeks means the
results can’t be reliably generalized to real-world situations. And importantly, a short trial like this may
miss side effects that only become apparent with long-term use.
In addition, the trial used a supplement that contained multiple ingredients. So, it’s IMPOSSIBLE to tell
which ingredient was responsible for the weight loss.
Ideally these initial results would be tested in a much longer trial involving hundreds of participants with
careful monitoring for side effects and controlling for confounding variables such as other ingredients.
Results from such a trial would allow for an informed decision about the safety and effectiveness of such
This example illustrates that unless such trial data is available, the claims regarding dietary supplements
and weight loss should be treated with caution.
Understanding safety concerns
A product isn’t necessarily safe simply because it’s natural. Though rare, some dietary supplements have
been linked to serious problems, such as liver damage.
Supplements can have strong effects. Ephedra (ma-huang) is an herb once used for weight loss. It’s now
banned by the FDA because it was associated with adverse effects, such as mood changes, high blood
pressure, irregular heart rate, stroke, seizures and heart attacks.
Some weight-loss supplements have been found to contain hidden ingredients, such as prescription
drugs, that may be harmful.
Research before you buy
It’s important to do your homework if you’re thinking about trying a weight loss supplement. Check
credible websites, such as those run by the U.S. Office of Dietary Supplements and the National Center
for Complementary and Integrative Health.
Also be sure to talk with your doctor before taking any supplement. This is especially important if you
have health problems, take prescription drugs, or are pregnant or breast-feeding.
Popular Weight Loss Supplements
In no particular order, here is an analysis of some of the most popular weight loss supplements. This is
by no means an exhaustive list. They are coded in the following manner: RECOMMENDED, PROCEED
WITH CAUTION, and AVOID
- Chitosan – This is a sugar that comes from the hard outer layers of lobsters, crabs, and shrimp.
a. How it works: Enthusiasts say it can block fats and cholesterol from getting absorbed by
b. Effectiveness: It has not been shown to be effective for weight loss.
c. Side Effects: Chitosan usually causes no side effects, but some people get an upset
stomach or constipation. If you are allergic to shellfish, you should not take chitosan,
because it is made from shellfish.
d. SUMMARY: No evidence that it is effective. It is often a component of weight loss
- Conjugated Linoleic Acid (CLA) – It is known as one of the “healthier” trans fats and is found
naturally in some fatty animal-derived foods like cheese and butter.
a. How it works: CLA may reduce appetite, boost metabolism, and stimulate the
breakdown of body fat.
b. 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.
c. 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
d. SUMMARY: CLA appears to be an effective weight loss supplement, but it may have
harmful effects in the long term.
- Glucomannan – It is a type of fiber found in the roots of the elephant yam, which is also called
a. 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.
b. Effectiveness: One clinical trial showed that taking glucomannan for 60 days could lower
body weight among overweight participants, but only if they were consistently taking
the supplement. 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.
c. 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.
d. 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
- Green Tea Extract – 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.
a. 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
b. Effectiveness: Many human studies have shown that green tea extract, when paired
with exercise, can increase fat burning and cause fat loss, especially in the belly area.
Additionally, all the health benefits of drinking green tea may also apply to green tea
c. 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.
d. SUMMARY: Green tea and green tea extract could increase fat burning slightly and may
help you lose belly fat.
- Green Coffee 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.
a. How it works: Caffeine can increase fat burning, and chlorogenic acid can slow the
breakdown of carbohydrates in the gut.
b. Effectiveness: 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
found that the supplement has a significant impact on minimizing body mass index.
Also, Green coffee bean extract may help lower blood sugar levels and reduce blood
pressure. It is also high in antioxidants.
c. 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
d. SUMMARY: 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.
- Guar Gum – This comes from the seed of the guar plant.
a. How it works: Like other dietary fibers, it may prevent fats from being absorbed into
your body and helps you feel full.
b. Effectiveness: Guar gum has been studied much more than other fibers for weight loss,
and most researchers say it’s not effective.
c. Side effects: gas and diarrhea
d. SUMMARY: It is not effective alone, but often found in other products as a “fiber”
- Hoodia – This is a plant that grows in the Kalahari Desert in Africa. The stem of the root was
traditionally used by Bushmen to cut their hunger and thirst during long hunts. It’s now
marketed as an appetite suppressant.
a. How it works: Hoodia contains P57, an ingredient that’s said to curb appetite by helping
you feel full.
b. Effectiveness: no credible evidence that it’s effective.
c. Side effects: can cause minor side effects such as headache, dizziness, giddiness, nausea,
and unusual skin sensations. Also, there is concern that hoodia might increase blood
pressure and heart rate.
d. SUMMARY: needs more investigation, no evidence that is safe or effective
- 7-Keto-DHEA – This is found naturally in your body.
a. How it works: It may help you lose pounds by speeding up the body’s metabolism and
converting more energy to heat instead of storing it as fat.
b. Effectiveness: In a couple of small studies, people who took 7-keto-DHEA — along with
moderate exercise and a reduced-calorie diet — lost significantly more weight than
those who were given a placebo
c. Side effects: can cause mild side effects such as nausea, dizziness, or low blood pressure
in some people.
d. SUMMARY: Might be effective, but there is NO high-quality evidence, so needs further
- Ephedra – This is an herb that’s also known as ma-huang. This is a different plant from a related
species that grows in North America. Ephedra contains the stimulant ephedrine. It is very closely
related to these manmade compounds found in some drugs: Pseudoephedrine and
a. How it works: suppresses appetite and increases fat burning.
b. Effectiveness: According to the FDA, there is little evidence that the herb helps except
for short-term weight loss.
c. Side effects: The FDA banned supplements with ephedra after the herb was linked to
serious side effects, including heart attacks, arrhythmias, strokes, psychosis, seizures,
and death. The FDA’s ban doesn’t apply to traditional Chinese herbal remedies or to
products such as herbal teas.
d. SUMMARY: It is a potent stimulant and is potentially effective for weight loss in the
short term. However, the side effects can be serious, so it should be avoided.
- Bitter Orange – The bitter orange tree is native to Africa and tropical Asia. It’s also grown in the
Mediterranean, California, and Florida. Bitter orange fruit rind contains synephrine, a stimulant
related to ephedrine.
a. How it works: Synephrine has similar mechanisms to ephedrine but is less potent. It
could help reduce appetite and increase fat burning.
b. Effectiveness: Very few studies have been done on synephrine, but many studies have
found that ephedrine can cause significant short-term weight loss, so it is “presumed”
that synephrine does the same.
c. Side effects: Like ephedrine, synephrine may have serious side effects related to the
heart. It may also be addictive.
d. SUMMARY: It is a potent stimulant and is potentially effective for weight loss in the
short term. However, the side effects can be serious, so it should be avoided.
- Garcinia cambogia extract – It’s a small, green fruit shaped like a pumpkin. The fruit’s skin
contains hydroxy citric acid, the active ingredient in garcinia cambogia extract, which is
marketed as a diet pill.
a. 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
b. 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 who were
overweight or obese, 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)
c. 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. Hepatotoxicity, or liver impairment, and some episodes of mania have also
been reported in conjunction with taking garcinia cambogia.
d. SUMMARY: Even though garcinia cambogia may contribute to modest weight loss, the
effects are quite small and may not be noticeable.
- Hydroxycut – 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.”
a. 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.
b. 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
c. Side effects: If you are sensitive to caffeine, you may experience anxiety, jitteriness,
tremors, nausea, diarrhea, and irritability. Hydroxycut products were removed from
shelves as a result of cardiovascular risks in 2004 and hepatotoxicity in 2009. Acute liver
injury has also related to using Hydroxycut supplements
d. 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
- Caffeine – Caffeine is the most 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 thought to be a metabolism booster, companies commonly add it
to commercial weight loss supplements.
a. How it works: Reduces appetite and increases energy expenditure by helping you burn
more calories via increased fat breakdown as well as through a process of body heat
production called thermogenesis.
b. Effectiveness: Some studies show that caffeine can cause modest weight loss in humans
c. 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.
d. SUMMARY: Caffeine can help boost metabolism and enhance fat burning in the short
term. However, a tolerance to the effects may develop quickly.
- Orlistat (Alli) – Orlistat is a pharmaceutical drug sold over the counter under the name Alli and
via prescription as Xenical.
a. 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.
b. 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. Also, Orlistat has been shown to reduce blood pressure slightly and
may reduce the risk of developing type 2 diabetes when used alongside lifestyle
c. 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. Following
a low-fat diet while taking orlistat is often recommended to minimize side effects.
d. SUMMARY: It 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. Obviously, it has
no effect on carbohydrate, protein, or alcohol calories that are consumed.
- Raspberry Ketones – substance found in raspberries that is responsible for their distinct smell. A
synthetic version of raspberry ketones is sold as a weight loss supplement.
a. 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.
b. 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% decrease in weight loss over 8 weeks when compared with a placebo. One
mouse study using massive doses showed some delay in weight gain.
c. Side effects: This may cause your burps to smell like raspberries. High doses of raspberry
ketones were also associated with higher blood sugar levels and higher levels of ALT, a
liver enzyme, indicating liver dysfunction.
d. 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
- Meratrim – 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.
a. 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.
b. 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 over an 8-week period. The Meratrim group lost 2.1 more
pounds on average than the placebo group. Another study suggested that Meratrim had
long lasting effects on appetite suppression.
c. Side effects: No side effects have been reported.
d. SUMMARY: One study showed that Meratrim caused weight loss and had several other
health benefits. However, the study was industry-sponsored with multiple flaws, so
more research is needed.
- Forskolin – extract from a plant in the mint family that is thought to be effective for weight loss.
a. How it works: It may raise levels of a compound inside cells called cAMP, which can
stimulate fat burning.
b. 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.
c. Side effects: There is minimal data on the safety of this supplement or the risk of side
d. SUMMARY: The two small studies on forskolin have shown conflicting results. It’s best to
avoid this supplement until more research has been done.
- Chromium – There are claims that chromium supplements can lower your appetite, help you
burn more calories, cut your body fat, and boost your muscle mass.
a. How it works: it is a mineral that enhances secretion of insulin, a hormone that’s
important for turning food into energy. Your body also needs it to store carbohydrates,
fats, and proteins.
b. Effectiveness: a review of 24 studies that checked the effects of 200 to 1,000
micrograms of chromium a day found that there aren’t any significant benefits.
c. Side effects: At less than 35 micrograms a day, chromium supplements are typically safe
for adults. Higher doses can cause insomnia, irritability, problems thinking, and
headaches. Also, some people have developed kidney damage when taking chromium.
You shouldn’t use it if you have kidney problems.
d. SUMMARY: Conflicting evidence about efficacy. Seems to be some benefit in those who
are deficient in Chromium. There seems to be increased maintenance of muscle mass
for those who are exercising and in a caloric deficit.
The Bottom Line
Of the 18 weight loss supplements mentioned, the ones backed by the “strongest evidence” are
glucomannan, CLA, orlistat (Alli), caffeine, green coffee extract, 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, green coffee 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. That said, it is convenient to have these supplements in a capsule or powder-drink form.
Long term, no supplement 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. It all boils down to CICO, Calories in and Calories Out!
Green Coffee Bean Extract
Green tea extract
Conjugated linoleic acid (CLA)