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The Article You Should Read Before Taking Any Weight Loss Medications

Written by Pietro Mignano, Pharmacist and Student of Nutrition, and Dr. William Yancy, Duke Diet and Fitness Center Program Director


If you are reading this article, probably as the majority of the Americans, you have seen some promising weight loss medication commercial on TV and thought: why not?


Weight loss medications can be helpful adjuncts to lifestyle change for people who struggle with weight management.

Unfortunately, however, weight loss medications are not magical bullets.

There are two principal mechanisms of these medications:

  • Appetite suppression
  • Interfere with the absorption of macronutrients  


To date, weight loss prescription medications as well as OTC’s (Over The Counter - meaning you don’t need a prescription), are not for everyone. According to guidelines released by the Endocrine Society, these drugs are appropriate for people who have a BMI (Body Mass Index) of 30 or higher. Doctors can also prescribe these drugs to patients whose BMI is between 27 and 30 if the patient has conditions related to increased weight such as high blood pressure, diabetes, sleep apnea or heart disease.

Before we go into details about how each of these medications work, you should know that it is still important to pay attention to the type and amount of the foods you are eating and to incorporate physical activity into your life before and while taking these medications. The medications do not take the place of these lifestyle improvements; think of them as adjuncts or enhancements. Also, know that it is common to regain weight after stopping a weight loss medication, so you need to have a long-term plan, which likely should include the medication. And lastly, check your health insurance to find out if the medication is covered because many are expensive.

The major benefit of each of these medications, of course, is weight loss. About 5-10% more of your original weight is lost as compared to patients trying to lose weight but not taking the medication. This weight loss leads to other improvements, too. Notably, blood sugar control improves with all of these medications given that weight loss is so beneficial for diabetes management.

Now let’s discuss a few of the most common medications and their properties:



In the US, Orlistat is available as a prescription and as an OTC (at half dose). The brand name is Xenical (Alli is the name of the OTC version). This drug interferes with the absorption of fat. It prevents the action of an enzyme which breaks down fat and allows it to be absorbed in the small intestine. This means that you will absorb less fat, so if you are on a diet that is rich in fat you will lose weight for sure!


While this sounds great, there is unfortunately a negative side to this as well: Fat passing from the small intestine to the large intestine can cause bowel pain, gas formation, bowel leakage, and steatorrhoea (“fatty diarrhea”). Therefore, people taking orlistat must follow a low fat diet to hopefully avoid these side effects. Furthermore, this drug makes it harder for your body to absorb vitamin A, D, E and K. So if you have decided to take this drug you should take a multivitamin, too, and at a separate time from taking the Orlistat.



This is a combination of two medications. Bupropion is commonly used to treat depression and to help people stop smoking. Naltrexone is a drug that has been approved to treat alcohol dependence. CONTRAVE acts on the brain influencing appetite and decreasing the hunger. Nausea is one of the most common side effects from this medication, but others include constipation, headaches, and insomnia. The most dangerous potential side effects are: increased risk of suicide in children or young adults who are depressed and increased risk of seizures in people with seizure disorders. You also can’t take narcotic (opioid) pain medications or drink alcohol excessively if you are taking Contrave.




Liraglutide, sold as Saxenda, is an injectable drug that was originally developed to treat type 2 diabetes (sold as Victoza). It has been shown that this medication can safely help obese people to lose weight even if they don’t have diabetes, but the exact mechanism is still not clear.  Liraglutide probably works in the brain, increasing satiety.

The most important thing to know before taking this drug is that in studies on rodents it has been shown to cause thyroid tumors. It’s unknown if it can happen to humans so far but people with a personal or family history of certain thyroid type cancers should not take this drug. Other side effects include nausea, vomiting and rarely, pancreatitis.



Lorcaserin is an antidepressant drug that works in the hunger control center of the brain. Here the drug blocks the hunger promoting a sense of satiety. Unlike many of the other weight loss medications, it does not cause increased heart rate or blood pressure so is safer in people with heart disease or hypertension. However, it cannot be taken in conjunction with many medications for depression and other psychiatric issues.

Some side effects include headache, constipation, dry mouth, fatigue and nausea and sometimes slowed thinking.



Amphetamines are a group of powerful drugs used in the past to sate the appetite. They were very common in the late 1980’s. They are psycho-stimulant drugs that produce increased focus and wakefulness in association with decrease appetite and fatigue. (For American movie lovers, this is the drug used by Sara Goldfarb to lose weight in REQUIEM FOR A DREAM). Unfortunately this drug has severe side effects such as: anxiety, fever, hypertension, constipation, palpitations, tremors, convulsions, stroke, heart attack, coma and death. And, of course, addiction. Therefore, they are illegal in the U.S.


So, in 1959 the FDA introduced a new drug that is amphetamine-like called Phentermine. The mechanism of action is similar to the amphetamine but with fewer side effects and much less potential for addiction. Phentermine is used on its own for weight loss, plus it is mixed with the Topiramate in QSYMIA in order to increase its satiating power and minimize the side effects. Both of the components act on the brain suppressing hunger but as always, there are potential side effects: depression, confusion, irritability, dry mouth, nausea, fatigue, eye pain, dizziness, and insomnia.

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With more than 40-year years of experience in delivering wellness and weight loss programs, the Duke Diet and Fitness Center has established itself as one of the leading weight loss and total body health destinations for health conscious individuals seeking a residential style health program focused on natural weight loss.

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