If you’re looking to lose some weight, it takes a lot of work. Naturally, diet pills that claim to lead to rapid weight loss seem like an easier option than the old-fashioned diet and exercise route (so archaic, right?). But the science behind weight loss pills is actually pretty iffy.
The majority of these infomercial-ready weight loss pills work by suppressing your appetite, increasing fat burning, or reducing how you absorb calories. But just because they can help you drop weight doesn’t mean it’s necessarily going to last — or that it’s safe.
There is evidence that some weight loss pills can be used safely to help you hit your goals. But taking just any diet pills you find in the supplement aisle can be dangerous.
Weight loss pills make a lot of promises, but how do you know it’s the real deal? Here’s where 14 popular diet pills stand:
|How it says it works
|Does it work?
|Helps improve metabolism and blood sugar levels.
|acid reflux, interactions with diuretics or insulin
|Keto pills (e.g., Rapid Tone)
|Puts your body in fat-burning ketosis.
|only in the short-term
|hunger hormones can increase after you stop taking them
|Makes you pee more to lose water weight.
|medication interactions, dehydration, kidney failure
|Boosts metabolism and increases fat burning.
|racing heart, anxiety, vomiting, jitters
|Green tea extract
|Caffeine and antioxidants aid in fat burning.
|Green coffee bean extract
|Burns and inhibits fat. Chlorogenic acid slows down the breakdown of carbs.
|caffeine side effects and diarrhea, possible allergy
|Burns fat with caffeine and herbs.
|no (recalled numerous times)
|anxiety, nausea, diarrhea, jitters
|Helps the intestines absorb less dietary fat.
|yes (with diet and exercise)
|no (flagged for possible liver damage)
|abdominal pain, gas, oily stools, frequent bathroom visits, headache, back pain, upper respiratory infection
|liver injury and digestive issues
|Makes you feel full.
|yes (with a healthy diet)
|medication interactions, bloating, gas, soft stools
|Conjugated linoleic acid (CLA)
|Suppresses appetite, breaks down fat, and boosts metabolism.
|yes (but serious side effects if used long term)
|digestive issues and fatty liver, inflammation, insulin resistance (if used long term)
|Breaks down stored fat.
|Bitter orange (synephrine)
|Suppresses appetite and helps burn fat.
|probably (but it has dangerous side effects)
|no (similar ingredients to ephedra, which the FDA banned)
|heart, digestive, and circulation issues, and potentially addictive
|Prescription medications (Contrave, Belviq*, Phentermine, Qsymia, Metformin)
|nausea, constipation, or diarrhea (Phentermine can also increase heart rate and blood pressure)
So what does science have to say about diet pills? Unfortunately, there’s not a lot of research to prove or disprove that many weight loss pills work. Here’s what we know.
1. Apple cider vinegar pills
Does it work? Probably not.
Apple cider vinegar (ACV) is essentially fermented apples that turn into vinegar. This can be made into pills and gummies marketed for weight loss. The acetic acid, B vitamins, and antioxidants in ACV may offer some health benefits. But taking apple cider vinegar for weight loss isn’t proven and studies are pretty limited.
A small 2004 study found that vinegar may have a role in regulating blood sugar after meals. A small 12-week study published in 2018 also found that participants who supplemented a reduced-calorie diet with ACV lost more weight than those who only followed the diet.
2. Keto pills (e.g., Rapid Tone)
Does it work? Technically, yes — but not in the long run.
“Keto pills” is an umbrella term for anything that claims it can help get your body into ketosis. The “Shark Tank” favorite Rapid Tone is one of these products.
These diet pills are effective at getting your body into a fat-burning state of ketosis. Research has shown that people in a ketogenic state have increased satiety hormones and decreased hunger hormones, which helps suppress appetite.
But even though these weight loss pills will help you shed pounds fast, it’s very likely the weight will return when you stop taking the pills. Studies show once people stop a ketogenic diet, hormones suppressing appetite increase and the weight comes back.
But that’s not a reason to take keto pills forever. Going keto long-term may also lead to negative health effects like nutrient deficiencies, low blood pressure, fatty liver disease, kidney stones, and eating disorders.
3. Water pills
Does it work? No. You’ll probably only lose 3 to 4 pounds of water weight, not actual fat.
Over-the-counter and prescription water pills are diuretics, meaning they make you pee by triggering your kidneys to get rid of extra water and salt. This helps you lose water weight and bloat.
A 2004 study found that water pills had basically no effect on weight loss. The pounds will return once you go back to your usual lifestyle. Plus, water pills can come with sketchy and even dangerous side effects like dehydration, headaches, cramping, dizziness, impotence, and seizures.
4. Caffeine pills
Does it work? Technically, yes — but not in the long run.
Caffeine may aid in weight loss by boosting your metabolism and fat burning, but it’s not likely to work for very long. That’s because your body builds up a tolerance to its effects.
5. Green tea extract
Does it work? Maybe.
According to a 2013 review of studies, some research has found that green tea extract can help with weight loss, but there’s not enough evidence to say for sure. It definitely won’t just melt away the pounds without diet changes and exercise.
6. Green coffee bean extract
Does it work? Maybe.
Green coffee beans (unroasted coffee beans) are another big weight loss supplement on the market that uses caffeine.
The caffeine in green coffee beans is thought to help weight loss by burning and inhibiting fat. Chlorogenic acid in the extract also slows down the breakdown of carbs in your digestive system. But there haven’t been many promising studies that weren’t funded by supplement companies.
A small, 8-week study found 20 subjects taking green coffee bean extract experienced more weight loss, reduced BMI, and suppressed appetite. But this small sample size isn’t enough to prove it works for everyone.
A 2011 review of three clinical trials also found the supplement helped with weight loss, but the authors stated there’s no clinical data available to conclude it works.
Does it work? Probably not. There are no reputable studies on the supplement itself, and online reviews are extremely mixed.
One of the most marketed and well-known weight loss pills, Hydroxycut is extremely controversial.
Over the years, the supplement has caused liver damage and heart-related deaths and has been recalled by the FDA numerous times for containing harmful ingredients like ephedra. Since it went back on shelves in 2010, Hydroxycut has changed its ingredients, but most medical professionals will caution you against using it.
Today’s Hydroxycut is a mix of caffeine, lady’s mantle extract, wild olive extract, komijn extract, and wild mint extract.
There are few to no studies on the different types of Hydroxycut, but we do know caffeine may help with weight loss.
8. Alli (orlistat)
Does it work? Yes. This one looks legit if you eat right and exercise too.
Alli is the lower-dose, over-the-counter version of orlistat (it’s also sold as the prescription drug Xenical).
In 2010, the FDA published a safety review of orlistat when people reported serious liver damage. The FDA could not find evidence that orlistat was the cause, but Alli changed its formula anyway.
The orlistat in Alli helps your intestines absorb less dietary fat by inhibiting the digestive enzyme lipase that breaks down fat. When you take Alli with a meal, roughly 25 percent of the fat you eat won’t be broken down — it’ll simply go straight through your bowels.
Numerous studies have shown that people who take orlistat with a calorie-restricted diet and exercise will lose more weight. But you don’t necessarily need it: A 2010 study actually found that eating a low carb diet was just as effective for weight loss as taking orlistat while eating a low fat diet.
Plus, Alli can come with uncomfy GI side effects like oily stools, diarrhea, fecal spotting, incontinence, and urgent bowel movements.
9. Garcinia cambogia
Does it work? Maybe.
Garcinia cambogia is a fruit that looks like a little green pumpkin. An extract from it is sold in pill form for weight loss.
Garcinia cambogia contains hydroxycitric acid (HCA), which is thought to suppress appetite. A 2011 study found that garcinia cambogia led to an average weight loss of about 2 pounds over several weeks. But more research is needed to clarify whether it works.
This diet pill is also linked to several reports of liver injury so it’s not risk-free.
Does it work? Yes. But with a healthy diet.
Glucomannan is an herbal supplement that’s extracted from elephant yam as a water-soluble dietary fiber.
Glucomannan is kind of a science experiment in your gut. Once ingested, it absorbs water and turns into a gel. This helps you feel full.
Research shows that glucomannan works when paired with a healthy diet and can also improve blood pressure, glucose levels, and cholesterol. A 2005 study found that glucomannan helped participants lose weight while on a 1,200-calorie diet — but this is significantly lower than the average calorie intake (about a 52 percent reduction for men and 40 percent for women).
11. Conjugated linoleic acid
Does it work? Yes, but it can really mess you up in the long term.
Conjugated linoleic acid, aka CLA, is a natural fatty acid used as a supplement for weight loss. CLA is thought to reduce appetite, break down fat, and boost metabolism.
A 2007 review of 18 studies found that participants taking CLA consistently lost weight for 6 months. However, the side effects are very serious and worth consideration. CLA can cause digestive issues and some nasty side effects (including fatty liver, inflammation, and insulin resistance) if used long term.
Does it work? Not likely. We know basically nothing about it.
Forskolin is extracted from the roots of the Indian coleus plant, a cousin of mint.
Forskolin is thought to help burn fat by raising your cells’ level of cyclic adenosine monophosphate (cAMP), a compound that helps break down stored fat. But TBH not much is known about this plant or how it affects weight loss.
There’s simply not enough data and too much conflicting information to tell if it’s safe, let alone if it works. So it’s best to avoid this pill until we have more research.
13. Bitter orange (synephrine)
Does it work? Probably, but its side effects can be dangerous.
The synephrine in bitter orange has very similar weight loss properties to ephedrine, the main component of ephedra (which was banned by the FDA for causing heart attacks and strokes).
While it’s similar to ephedrine, synephrine is less potent. It potentially helps weight loss by reducing appetite and helping you burn more fat. But, there haven’t been many studies on synephrine and the side effects can be major.
The NCAA lists synephrine as a banned stimulant for its athletes. The synephrine in bitter orange can cause heart, digestive, and circulation issues and is potentially addictive.
14. Prescription pills
Do they work? Maybe.
OK, so technically there are more than 14 pills on this list. There are several prescription drugs used to aid weight loss, but these are typically only prescribed for folks who are obese or overweight. These are not a quick fix to help someone shed a few pounds.
Prescription weight loss pills generally work by suppressing appetite and are combined with diet and exercise. Most are designed to support long-term weight loss plans created with a healthcare professional.
The most popular prescription weight loss prescription pills are:
So do they actually work? That’s up for debate. Contrave, Belviq*, Phentermine, and Qsymia have only been studied in participants who are obese and overweight. Most of these meds show pretty minor weight loss and only Qsymia has shown somewhat promising results after a year.
Metformin is actually a diabetes medication used to regulate blood sugar levels and its overall weight loss effects are also inconclusive.
Just because most weight loss pills don’t work doesn’t mean they’re risk-free. Most diet pills come with side effects. Peep these side effects before you start:
- ACV pills. The acidity can give you acid reflux. ACV can also interact with other diuretics and insulin, so you should avoid it if you have type 1 diabetes. Your kidneys could have trouble processing the extra acid if you have chronic kidney disease.
- Water pills. These are really intended to treat high blood pressure and can interact with other medications. Plus, they can overload your kidneys, leading to kidney failure (yikes!). Frequent urination can also lead to dehydration.
- Caffeine pills. Too much caffeine can make your heart race and cause anxiety, vomiting, and jitters. It’s safe to consume 400 to 500 milligrams of caffeine a day, but if you’re drinking caffeinated beverages and taking these pills, it’s easy to go overboard.
- Green tea extract. There have been reports of liver damage in people who took green tea extract.
- Green coffee bean extract. You could face the same side effects as caffeine — plus, diarrhea is possible thanks to the chlorogenic acid. You can also be allergic to green coffee beans.
- Hydroxycut. Like too many cups of coffee, the caffeine in Hydroxycut can cause side effects such as anxiety, nausea, diarrhea, and jitters.
- Alli. You may experience digestive issues like abdominal pain, gas, oily stools, and more bathroom visits. Headache, back pain, and upper respiratory infection are also possible.
- Carcinia cambogia. There are several reports of liver injury, while some folks may just have minor digestive issues.
- Glucomannan. You may have bloating, farting, and soft stools. It can also mess with some medications.
- CLA. If used long term, you may experience digestive issues, fatty liver, inflammation, and insulin resistance.
- Bitter orange. The Synephrine in bitter orange can cause heart, digestive, and circulation issues and is potentially addictive.
- Prescription weight loss pills. Thesecan cause nausea, constipation, or diarrhea. Phentermine also stimulates the central nervous system, which increases your heart rate and blood pressure.
Weight loss supplements are extremely understudied and most have no evidence to support they work.
Because many diet pills are considered dietary supplements, they are not regulated by the FDA in the same way as medications. Basically, companies creating these products are responsible for testing and approving their safety, not the FDA. This can lead to safety and quality control issues, plus misleading claims on how well these weight loss supplements actually work.
But some weight loss pills are actually categorized as medications. These do have FDA approval and are prescribed by a healthcare professional to help weight loss.
Weight loss pills vary greatly in their ingredients and effectiveness. Some have been proven to help with weight loss, others not so much. If you’re interested in trying a weight loss pill, always consult your healthcare professional to determine which option is right for you and safe to use.
Remember that diet, exercise, and a long-term plan created with a healthcare professional are ultimately your best options for successfully losing weight.
Weight loss pills can be a quick fix, but they won’t help you maintain a healthy weight in the long run and could even be harmful.