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Are Diet Pills bad for you? (Reviewed by Science)

Are Diet Pills bad for you? (Reviewed by Science)

  • In this article, we will investigate if the current research supports the safe use of diet pills.
Diet Pills

With 39% of individuals in United States being obese, many people are looking to alternative ways to lose weight[1]. Thus, diet pills and supplements have popped up everywhere to help.

FDA Regulation

Before taking a diet pill or supplement, it is important to know the difference from a safety standpoint.

The U.S. Food and Drug Administration (FDA) regulates prescription drugs, nonprescription drugs, and dietary supplements. Requirements for each are different though.

Prescription and non-prescription diet pills (drugs) must be proven safe and effective in studies before being sold to the public, while dietary supplements do not need approval from FDA before being put on the market[2].

This makes dietary or weight loss supplements potentially more dangerous as consumers are relying solely on companies for safety on a product. Dangerous weight loss supplements may be removed from the market if discovered to not meet FDA guidelines, although this finding maybe after reports of adverse events or side effects.

Health groups, like Public Citizen Health Research Group, have also raised concerns and started petitions on FDA approved synthetic diet pills after further research is conducted. The FDA does not deny unanswered long-term safety concerns but admits that research is not sufficient to justify rescinding approval.

Whether you are interested in taking a diet pill or supplement, it is important to discuss with your physician to ensure safety with your body.

This article will focus on diet pills only- the types, possible benefits, and main concerns.

What are the Types of Diet Pills?

Diet pills are divided into three categories based on what they do in our bodies. FDA has approved certain formulations for each type of diet pill.

Each diet pill appears to have its perks but, like any medication, may have side effects.


Stimulants affect the central nervous system to increase energy and curb appetite.

A study published by the American Diabetes Association conducted a 56-week study with overweight/obese individuals with type 2 diabetes[3].

The participants were divided into two groups. One group was the placebo group and the other group received the stimulant, phentermine/topirate extended-release, to compare the safety and efficacy of stimulant use for weight loss.

Both groups, with lifestyle modification, had weight loss over the 56-week period. The placebo group lost 2.7% body weight while the group receiving the stimulant loss of 9.4% body weight. Researchers reported paraesthesia, constipation, and insomnia were common adverse reactions.

Unfortunately, the biggest concern with stimulants is the risk of dependence. Many people become tolerant to the dosage of the stimulant and eventually increase the amount they are taking. This type of behavior is a common trait of addition.

Common Stimulant Pills & Side Effects

Generic Name Brand Name Common Side Effects
Benzphetamine Didrex® Headaches, dizziness, nausea, insomnia, sweating, increased blood pressure and heart rate, restlessness, anxiety, and dependence.
Diethylpropion Tenuate®, Tepanil® Constipation, restlessness, dry mouth, nervousness, insomnia, and dependence.
Fenfluramine Pondimin® Damages heart valves, primary pulmonary hypertension, increased heart rate and blood pressure, restlessness, insomnia, and anxiety.
Methamphetamine Desoxyn® Increased blood pressure and heart rate, restlessness, insomnia, nervousness, dependence, and withdrawal if stopped.
Phendimetrazine Bontril®, Prelu-2®, Plegine® Headaches, dizziness, nausea, insomnia, sweating, increased blood pressure and heart rate, restlessness, anxiety, and dependence.
Phentermine Adipex®, Ionamin®, Suprenza® Headaches, dizziness, nausea, insomnia, sweating, increased blood pressure and heart rate, restlessness, anxiety, and dependence.
Phentermine and topirate Qsymia® Tingling skin, dizziness, altered taste, insomnia, constipation, and dry mouth.

Appetite suppressant

Appetite suppressants target neurotransmitters, serotonin, and norepinephrine, in the brain to decrease appetite by increasing the feeling of fullness.

One appetite suppressant, lorcaserin, was studied on 12,000 obese or overweight individuals.

Participants took either lorcaserin or an inactive placebo pill twice a day. The average participant was followed for slightly more than three years.

After 40 months, participants taking lorcaserin lost approximately 9 pounds, compared to less than 5 pounds from those taking the placebo pill. Although the people taking lorcaserin loss more weight, the rate of side effects such as headaches, fatigue, dizziness, nausea, and diarrhea was twice as high.

See Also
Keto Meal Plan

Common Appetite Suppressant & Side Effects

Generic Name Brand Name Common Side Effects
Bupropion and Naltrexone Contrave® Headache, nausea, vomiting, dizziness, dry mouth, diarrhea, constipation, hot flashes, and unpleasant taste.
Liraglutide Saxenda® Nausea, vomiting, diarrhea, constipation, heart burn, fatigue, stomach pain, gas, and dry mouth.
Lorcaserin Belviq® Headache, nausea, dizziness, dry mouth, fatigue, feelings of euphoria or dissociation can occur at high doses.
Sibutramine Meridia® Headache, dry mouth, constipation, insomnia, runny nose, and sore throat.

Fat inhibitor

Fat inhibitors work by preventing fat absorption in the gastrointestinal tract.

People who take fat inhibitors are highly encouraged to follow a low-fat diet as side effects, like loose stools and oily spotting will worsen with more fat consumed.

Individuals also have a decrease in the absorption of fat-soluble minerals and vitamins such as vitamins E, A, D, and K. Supplementation to replace these vitamins are important to prevent deficiency.

A study conducted in 2011 had 80 obese participants that were randomized into two groups[5]. One group received Orlistat three times a day with meals, while the other group took an inactive placebo pill three times a day with meals.

Over a 6-month period, the average weight loss for participants taking Orlistat was 10 pounds compared to 5.5 pounds from the placebo group.

Along with gastrointestinal side effects, there is a concern that orlistat may cause cancer. Studies have found a significant increase in breast cancer among orlistat users and also an increase in aberrant crypt foci[6]. This substance is potentially a precursor of colon cancer.

Common Fat Inhibitor and Side Effects

Generic Name Brand Name Common Side Effects
Orlistat Alli®, Xenical® Softened stools, gas, fecal urgency, oily spotting, fecal incontinence, and risk of serious liver injury.

Bottom Line

All studies reviewed in this article showed a modest amount of weight loss and included a lifestyle modification by participants, either change in diet or physical activity.

Any diet pill can be unsafe and dangerous if not taken under medical supervision.

If any pill claims to produce significant weight loss in a short period, this is a red flag. This could be a sign that it is dangerous or simply ineffective.

A diet pill will not be the “holy grail” for weight loss. If you are interested in a diet pill, talk to your doctor about the risks, benefits, and cost of each.


[1] Centers for Disease Control and Prevention Adult Obesity Facts
[2] U.S. Food & Drugs Dietary Supplements
[3] Timothy Garvey1,2?, Donna H. Ryan3, Nancy J.V. Bohannon4, Robert F. Kushner5, Miriam Rueger6, Roman V. Dvorak7 and Barbara Troupin7
[5] Indian J Endocrinol Metab2011 Apr-Jun; 15(2): 99–104. doi: 10.4103/2230-8210.81938
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