How safe are weight loss drugs?

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Everyone seems to be looking for a quick way to lose weight, but are weight loss drugs safe, or part of disordered eating practices?

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Weight loss drugs overview

The pharmaceutical industry has created a number of different drugs over the years designed to assist with weight loss. Drugs that are taken for the purpose of losing weight quickly are sometimes called “anorectics”. Some have proven to be dangerous and have been taken off the market, particularly a drug called Fen-phen which was widely available in the 1990s but soon found to cause cardiovascular problems. (5) 

Other anorectic drugs, or weight loss drugs, are still used with good effects, and have been proven to be safer. However they almost always require a medical evaluation by a doctor prior to starting, and all of them have some potentially serious side effects. For example, drugs that interfere with fat absorption such as orlistat can lead to oil spotting, gas, and soft stools. (2) Glucagon-like peptide-1 (GLP-1) receptor agonists such as liraglutide or semaglutide can commonly cause heartburn, diarrhea, gas, constipation, nausea, vomiting and hypoglycemia, particularly if used with insulin.other side effects. How can you eat regular meals that are healthy if you have to battle against these GI disturbances? (2)

If you are using a weight loss drug, you should always be using a prescription given by a doctor, and make sure you are having regularly scheduled visits with that doctor to ensure you are getting the proper laboratory and physical monitoring that you need to keep you healthy and safe while still losing weight.

Common weight loss medications 


Phentermine, also known by its brand name Adipex, is one of the few FDA approved medications for weight loss. It is an amphetamine medication and acts by increasing the sympathetic tone of the body which in turn decreases the hormones that increase appetite such as ghrelin. It is relatively safe in most individuals, but can increase blood pressure, which is why it needs to be prescribed and monitored by a clinician.

Phentermine is a controlled substance and thus requires a physician with a Drug Enforcement Agency (DEA) license to prescribe it. It is sometimes sold in conjunction with topiramate, an anti-seizure medication that also causes some weight loss. The brand name for this combination pill is called Qysmia. Both Adipex (Phentermine alone) and Qysmia (Phentermine-Topiramate) are often not covered by insurance plans and can be expensive, costing anywhere from $20-200 dollars per month on average. 

GLP-1 agonists

These often go by the names Semaglutide (Ozempic), Liraglutide (Victoza) or Dulaglutide (Trulicity). GLP-1 agonists are a class of medications that are usually used for diabetes, although they can and often are prescribed off-label for weight loss. They lead on average up to a 5-10% body weight reduction. They come in injectable forms, usually requiring either once a day or once a week injection which can be done by the patient at home. They work by causing increased secretion of insulin from the pancreas.

Unlike Phentermine, GLP-1 agonists are not stimulants and do not decrease weight by decreasing appetite. They do have some side effects - they can cause nausea and vomiting or diarrhea/abdominal cramping, particularly in the first month of use. They are also contraindicated in anyone with certain neuroendocrine disorders, or in anyone with a history of pancreatitis. They therefore also require monitoring by a doctor, and are prescription only. They also may require prior authorization from an insurance company and can be expensive to buy out of pocket. 


This is an oral medication that works by decreasing fat absorption into the body. On average, it leads to about a four percent reduction in body weight. As a result, it causes bloating, flatulence, and sometimes diarrhea. It is often difficult to tolerate which is why it is not commonly prescribed these days, although is generally considered safe, and is available over the counter in most states. In addition, it is relatively inexpensive compared to other weight loss medications. 

Buproprion-naltrexone (contrave)

This is a combination of two medications that can help with weight loss. Because it is brand name only, it can be an expensive medication and not all insurances will cover it.

Most doctors agree that lifestyle changes, healthy eating habits, and moderate exercise continue to be the best treatment for long-term weight loss. The benefits of lifestyle habit changes are far-reaching and many. You have the chance to look better, feel better, start doing healthier things. 

However, in certain circumstances and for certain patients, pharmacologic assistance with weight loss might be appropriate. But, “diet pills” may be used for the shortest amount of time necessary to help with weight loss, and should always be prescribed in consultation with a medical doctor.

Disclaimer about "overeating": Within Health hesitatingly uses the word "overeating" because it is the term currently associated with this condition in society, however, we believe it inherently overlooks the various psychological aspects of this condition which are often interconnected with internalized diet culture, and a restrictive mindset about food. For the remainder of this piece, we will therefore be putting "overeating" in quotations to recognize that the diagnosis itself pathologizes behavior that is potentially hardwired and adaptive to a restrictive mindset.


  1. Craddock D. Anorectic drugs: use in general practice. Drugs. 1976;11(5):378-93. 
  2. Side effects of weight loss drugs (diet pills). (n.d.). Retrieved May 19, 2022, from 
  3. The most important lesson from 83,000 brain scans - youtube. (n.d.). Retrieved May 19, 2022, from 
  4. Craddock D. Anorectic drugs: use in general practice. Drugs. 1976;11(5):378-93.
  5. Dickerson LM, Carek PJ. Drug therapy for obesity. American Family Physician. Apr 1, 2000; 61(7):2131-2138.
  6. RxList. (2021, October 12). Fastin (phentermine): Uses, dosage, side effects, interactions, warning. RxList. Retrieved May 19, 2022, from 
  7. U.S. National Library of Medicine. (n.d.). Chlorpheniramine: Medlineplus drug information. MedlinePlus. Retrieved May 19, 2022, from 
  8. WebMD. (n.d.). Maois for bipolar disorder: Types, uses, side effects. WebMD. Retrieved May 19, 2022, from


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