Prescription Weight Loss Drugs: What You Need to Know

By MaryAnn DePietro, CRT. May 7th 2016

About one in three adults in the United States are obese, according to the Centers for Disease Control and Prevention. Obesity puts a person at a much higher risk of problems, such as type 2 diabetes, heart disease and hypertension. Although many people who are overweight try to shed the pounds, losing weight is not always as easy as eating healthy food and exercising. When an individual is significantly overweight and needs a little additional help to lose weight, prescription weight loss medications may be prescribed.


There are a few different types of weight loss medications that are approved by the U.S. Food and Drug Administration. Some medications are only intended for short-term use, while others can be taken for a longer period of time. Prescription weight loss medication is usually classified as either an appetite suppressant or one which blocks fat absorption.

There are a few common prescription weight loss medications, which include the following:

  • Diethylpropion: Approved by the U.S. Food and Drug Administration as a short- term weight loss medication, diethylpropion works by decreasing a person’s appetite. The exact amount of time it can be taken may vary slightly, but it is usually only recommended for a few weeks. Diethylpropion is usually taken up to three times a day about 60 minutes before eating.
  • Phentermine: This medication is also only approved for short-term use, and is usually only taken for 6 weeks or less, according to the U.S. National Library of Medicine. The medication also works by suppressing appetite and causing a feeling of fullness for longer periods of time. The medication should be used with caution, since it can be habit forming. Phentermine is usually taken about a half hour before meals. An extended release pill is also available, which can be taken once a day.
  • Orlistat: This type of weight loss medication works by preventing the absorption of some of the fats in food. It is taken before a person eats a meal which contains fats. The medication does not have to be taken, if the meal eaten does not contain fat.


Prescription weight loss medications are not intended for people who have a few extra pounds they want to lose. Because the medications can cause side effects, physicians must weigh the benefits against the risks. In most cases, weight loss medications are only prescribed for people who are significantly overweight and have a body mass index of 30 or greater. In addition, people who have a body mass index of over 27, but also have medical conditions associated with obesity may also be prescribed the medication.


Although weight loss varies according to the Mayo Clinic, people taking weight loss medication on average lose between 5 and 10 percent of their body weight, which can greatly improve health. It is also important to understand those who are prescribed the medication are also instructed to eat a healthy diet and exercise regularly. The weight loss is likely due to the combination of all three factors and not the medication alone.

There does not appear to be any specific research which indicates, people who take weight loss medication keep the weight off better than those who don’t use medication.

Maintaining weight loss is difficult for many individuals including those who take weight loss medication. Lifestyle changes including consistently eating healthy and staying physically active is critical to keeping weight off for anyone.

Side Effects

There are possible side effects, which may occur when taking prescription weight loss medication. The severity of side effects will vary greatly among those taking weight loss pills. In addition, side effects often depend on which medication is prescribed. For example, orlistat may cause loose stools, gas, diarrhea, stomach pains and headache. In some people, it can also cause liver damage.

Phentermine can also cause side effects, such as nervousness, dry mouth, constipation and nausea. Serious side effects, which are possible, include an increase in blood pressure and trouble sleeping. Side effects of diethylpropion include anxiety, depression, dry mouth and unpleasant taste. Individuals taking the medication should also be aware of possible serious side effects including heart palpitations, rash and blurred vision.

Patients always need to tell their doctor what other medications they are taking including herbal remedies before they start taking weight loss pills. The weight loss medications can interact with other medications being taken and cause additional side effects.

It is clear being overweight or obese can cause serious medical problems. In certain instances, medication can aid an individual with their weight loss goals. It is important to remember, medication needs to be combined with exercise and healthy eating in order to lose weight. Since medications may cause side effects in some people and some medications are only meant to be taken for a short time, it is essential to always follow a doctor’s instructions.


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