Do Diet Pills Work? Here's What Dietitians Want You to Know

From buzzy weight-loss medications to over-the-counter diet pill supplements, we spoke with dietitians to separate fact from fiction when it comes to these pills and shots.

a photo of hands holding a knife and work, digging into a plateful of pills
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On the heels of celeb tales about their experiences with Ozempic—and the fact that the shot originally developed to help treat type 2 diabetes was experiencing shortages due to its popularity—the conversation around this weekly shot and diet pills and supplements have reached a fever pitch.

That's why, in January 2023, the American Academy of Pediatrics announced new guidelines about how doctors might consider treating children whose body mass index (BMI) qualifies them as having obesity. If pediatricians follow these recommendations, kids as young as 12 could be prescribed "obesity weight-loss pharmacotherapy, according to medication indications, risks and benefits, as an adjunct to health behavior and lifestyle treatment."

With teens and adults as the target market for weight-loss medications and diet pills, read along to learn about this complex and controversial topic.

How Do Diet Pills Work?

Two very different types of medicines fall under the umbrella of diet pills or weight-loss medications. First, the prescription weight-loss shots and pills you get from a health care provider, which are regulated by the Food and Drug Administration and require clinical trials to support their efficacy and safety. And second, the over-the-counter supplements and diet pills that aren't regulated by the FDA, which often claim to rev metabolism or "detox" the body.

Both have become quite popular: The National Institutes of Health estimates that about 15% of adults in the U.S. have tried a weight-loss supplement at some point in their lives, and even more are hopping on the prescription Ozempic train.

"Diet pills or weight-loss supplements work in a wide variety of ways and are intended to help those with weight-loss struggles. They often promote appetite suppression, a reduction in dietary fat absorption, decreased cravings or by increasing the sense of fullness," explains Pedro Leon, RDN, LDN, a clinical dietitian for Northwest Community Healthcare in Arlington Heights, Illinois.

FDA-approved options are generally recognized as safe when used as prescribed, according to Leon, and the American Heart Association and the American College of Cardiology report that these weight-loss medications can work. On average, an individual can anticipate losing about 5% to 10% of their weight in the first six months of use, initial studies suggest, such as one published in JAMA Network Open in 2022, but it's simply too soon to know the long-term health impacts.

"There aren't substantial long-term and large research studies about whether some of these medications can hold up to their claim and effectiveness," adds Crystal Scott, M.S., RD, LD, CDCES, CSSD, CSP, a registered dietitian in Dallas, Texas. "As someone who has been a practicing dietitian for 16 years, I would recommend anyone looking into diet pills to evaluate their relationship with foods and behavior around foods first. Some people who start Ozempic may have a challenging relationship with food. By addressing that first, the need for these medications would decrease," and the health outcomes would likely be more sustainable over the long term.

As far as those infomercial-promoted diet pills that often take up prime real estate at pharmacies and supplement shops, the Government Accountability Office concluded that "little information on potential safety concerns from dietary supplement AERs [adverse event reports] is publicly available and accessible to consumers, health care practitioners, and others." In fact, some options are absolutely unsafe and have led to serious illnesses and even deaths, the FDA confirms.

Especially among the less-regulated mail-order and over-the-counter options, "These can interact or interfere with certain medications, so you should always speak to your health care provider about potential benefits and risks before starting any supplement or medication," Scott says.

Definitely proceed with caution and don't use these without medical supervision, especially if you have any conditions such as high blood pressure, diabetes, depression, liver disease or heart disease, or if you're pregnant, breastfeeding, have digestion issues or have a history of disordered eating.

If you have weight-loss goals, your best bet, according to Roxana Ehsani, M.S., RD, CSSD, a Miami-based board-certified sports dietitian, is to work with a registered dietitian. It's also helpful to consider your "why." Research hints that healthy habits such as physical activity and eating more fruits and vegetables have much more to do with wellness outcomes than the number on the scale or your BMI.

The Most Popular Diet Pills, Weight-Loss Medications and Supplements

Ahead, a debrief on the aforementioned Ozempic and some other frequently advertised diet pills.


Although the celeb headlines speak to its use as a weight-loss medication, Ozempic (semaglutide) was originally developed for people with type 2 diabetes to help them manage their blood sugar and A1C levels. This class of medicines, GLP-1 agonists, works by increasing the amount of insulin produced by the pancreas and decreasing the amount of glucagon produced by the liver—essentially reducing hunger. In a study published in March 2021 in The New England Journal of Medicine, researchers found that after 68 weeks of weekly injections, participants decreased body weight by 14.9% compared to the placebo group.

"Thus far, Ozempic has been seen to help individuals with weight loss either with or without the presence of diabetes," Leon says. So with that being the case, semaglutide is marketed by the brand name Wegovy when prescribed for weight loss among those who haven't been diagnosed with type 2 diabetes. "The best results have been seen using semaglutide along with lifestyle modifications."

The existing literature related to Ozempic/Wegovy and weight management involves trials that are fairly small and short-term. Leon adds that more independent studies are needed to determine a successful long-term solution. Some common side effects have been reported, such as nausea and diarrhea.

Other FDA-approved weight-loss shots and pills include Contrave, Qsymia, Saxenda and orlistat.


Speaking of orlistat (common brands include Xenical and Alli), since it also ranks among the most popular weight-loss medications, we'll dive deeper here, too.

"This medication prevents some of the fat found in food from being absorbed in the intestine. The unabsorbed fat exits the body through the stool," Ehsani clarifies.

Since this is the mechanism, this FDA-approved medication can cause gas, loose stools, oily or fatty stools, difficulty controlling bowel movements, irregular menstrual periods in females and oily spotting on clothing. Not only that, orlistat may lead to difficulty breathing or swallowing, itching, rash, hives, excessive weakness, vomiting or yellowing of the skin or eyes, Ehsani says. According to StatPearls, it may also impact the absorption of other important medications taken by those who have experienced blood clots, organ transplants, irregular heart rhythms and more. (Clearly, serious matters.)


It's not just found in coffee, tea, chocolate and energy drinks anymore.

"This stimulant for weight loss is most commonly used as an appetite suppressant and for its thermogenic, or metabolism-boosting, qualities. In the short-term, it can have a small positive effect, but no substantial evidence shows that it helps long-term," Leon says.

What we do know about the long haul, however, is that high consumption of caffeine supplements appears to actually contribute to weight gain, hormone imbalance, increased blood pressure, insulin resistance and sleep disturbance. So enjoy your cup of coffee in the morning if you like, but know that studies don't support consuming caffeine in supplements as a long-term weight-loss solution.

High doses of caffeine found in caffeine diet pills can be fatal, Ehsani continues, and can be especially harmful to teens, young adults and anyone sensitive to the effects of caffeine. It may also cause side effects such as anxiety, sleep issues like insomnia, dehydration, digestive issues, rapid heart rate, diarrhea or vomiting.

"The FDA says that up to 400 milligrams of caffeine a day is OK, but some of these may be higher, and some pills in combination with a cup or two of caffeinated beverages may be very dangerous," Ehsani says.

Green Tea Extract

Like the tea it shares its name with, green tea extract is rich in catechins, antioxidants and caffeine. Leon explains that the latter's thermogenic (calorie-burning) effect has been promoted as a way to increase energy expenditure and fat oxidation.

"Several clinical trials found that it can possibly have a modest effect on body weight," Scott says.

However, if consumed in high doses or for an extended period, green tea extract can cause gastrointestinal side effects like nausea, vomiting, diarrhea and abdominal pain. Beyond that, excess green tea extract can lead to serious issues, including heart palpitations and liver damage or failure.

"Weight-loss benefits are seen in limited cases and tend to be modest at best. It's best to enjoy your green tea for its healthy, antioxidant benefits," Leon says.

If you follow his guidance and sip green tea instead of a supplement, you might score some blood sugar and inflammation-taming benefits.

Green Coffee Bean Extract

For this diet pill, manufacturers sell an extract made from coffee beans that have not been roasted. Again, it provides a source of caffeine, which can increase resting metabolic rate and fat metabolism. The levels of chlorogenic acids found in green coffee bean extract are also said to reduce carbohydrate absorption in the digestive tract.

"The studies done on green coffee bean extract have been short and with a small sample size; therefore, there are limitations, and researchers can't yet verify whether it's effective or safe. Also, there isn't a dosage amount for green coffee bean extract, so it's hard to say what amount is OK compared to what amount is unhealthy and dangerous to health," Ehsani says.

Conjugated Linoleic Acid (CLA)

Conjugated linoleic acid (CLA) is a fatty acid naturally found in food like beef and dairy products.

In diet pill form, CLA marketers claim that it can help burn body fat and, as a result, lead to weight loss.

"The studies that 'work' have been only done on animals, not humans. Among people, the results were not clear, and people only lost 1 pound over the course of a 12-week study. There's very little evidence showing it actually helps or works. More research studies need to be conducted before I'd recommend this," Ehsani says.

Side effects of CLA supplementation can trigger inflammation. Additionally, it may lead to liver enlargement, insulin resistance, abdominal discomfort and pain, constipation or diarrhea, and adverse effects on blood lipids, Leon and Scott add.


Marketed for weight loss and as a "fat burner," Hydroxycut was originally released with a combination of caffeine and ephedra. In fact, after its release on the market, ephedra was found to be poisonous and deadly, per a 2015 article published in The New England Journal of Medicine.

After reformulation to remove the now-banned substance, ephedra, "it now contains coffee extract, apple-cider vinegar, plum, baobab extract, cardamom, caffeine from coffee extract, and high doses of vitamin B12," Ehsani says. "There is no solid evidence or research showing that these supplements are even effective."

Reported adverse side effects from users include jitters, stomachaches, rapid heartbeat, excessive sweating and nausea. And Leon says that even after reformulation to remove the now-banned ephedra, Hydroxycut may lead to liver disease, high blood pressure, seizures, heart disease and death.

"This is one diet pill you should steer clear of. Any short-term benefit is largely outweighed by its long-term health complications," Leon says.

The Best and Healthiest Way to Lose Weight

The dietitians agree that the best way to lose weight and keep it off is to eat a well-balanced, colorful, nutritious diet focusing on nutritious foods, scoring enough sleep, integrating some physical activity and carving out time for self-care stress reducers.

Here are a few pro tips to get you started:

Frequently Asked Questions

1. Can doctors prescribe diet pills?

Yes, doctors can prescribe certain FDA-approved weight-loss medications like Wegovy (semaglutide), Contrave, Qsymia, Saxenda and orlistat. Many other unregulated diet pills are on the market, though, and are available via mail or over the counter at pharmacies and supplement stores.

2. Are all diet pills bad for your health?

We simply don't know enough about most of them to confirm their long-term safety. The FDA-approved pills and shots appear to be safe for use for at least when they've been studied and among specific populations, but more research is needed to confirm their eventual safety and effectiveness.

3. Who should avoid diet pills?

Speak with your primary care doctor before beginning any new medication or supplement. Everyone, especially those with high blood pressure, diabetes, depression, liver disease or heart disease, or if you're pregnant, breastfeeding, have digestion issues or have a history of disordered eating, should consult with a health care provider before using weight-loss medications.

The Bottom Line

Even though many are marketed as such, "these products are not magic pills and commonly fail when used alone," Leon says. "Most, if not all, will carry a disclaimer that they are effective along with sustainable nutritional, physical activity and behavioral changes."

Instead of turning to what may be a short-term fix—with some very real potential for side effects—if you have weight-loss goals, turn to healthy habits that can help you reach them. EatingWell dietitians recommend trying simple steps like filling half your plate with veggies, mixing up your macronutrients (carbs, fat and protein), consuming more fiber and integrating more physical activity.

Consult with a registered dietitian if you'd like additional guidance, and don't begin taking any new medication, FDA-approved or otherwise, without first discussing it with your doctor.

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