A Comparison of Xenical and Phentermine

When you want a helping hand to lose weight, the choice of weight loss drugs can be overwhelming.

As part of our series on weight loss drugs, we will explore the pros and cons of Xenical and phentermine, so you can see if one of these medications might suit your weight loss goals.

What Is Xenical?

Xenical is the brand name for 120mg of orlistat. It is a prescription medication that was approved by the Food and Drug Administration (FDA) in 1999 for obese and overweight adults and adolescents aged 12 and over.

In general, it is prescribed for obese patients with a body mass index (BMI) of 30 or higher. However, those with a BMI of 27 or higher who also have weight-related complications such as high blood pressure are also eligible for treatment with Xenical. (1) (2)

Xenical helps patients lose weight by reducing dietary fat absorption in the intestines. Fat that is not absorbed passes through the digestive system and is excreted in the feces. Although some fat may still be eaten, Xenical causes an overall caloric deficit. This can make weight loss easier for some people. For maximum weight loss, Xenical should be taken in conjunction with a low-fat diet. (3)

In a 24-week clinical trial, obese patients who took 120mg of orlistat three times daily lost approximately 4.65kg in weight, compared to the placebo group with an average weight loss of around 2.5kg.

Taking Xenical was also shown to reduce the BMI, waist circumference, cholesterol levels, and an individual’s risk of developing type 2 diabetes. (4) (5)

What Is Phentermine?

Phentermine tablets or capsules contain the active ingredient phentermine hydrochloride.

This weight loss option is prescribed to patients with a BMI of ≥30, or ≥27 with weight-related complications. Phentermine is not an amphetamine, but the chemical structures have some shared similarities. It is sometimes prescribed under the brand name Adipex-P or Lomaira. 

As a central nervous system stimulant, phentermine increases the heart rate, raises energy levels, and reduces feelings of hunger. This can make it easier to lose weight, but for best results, you will also need to follow a low-calorie diet. (6)

In a 12-week clinical trial of 711 overweight and obese adults, over 45% lost at least 5% of their body weight, with an average weight loss of around 4kg. Reductions were also seen in waist circumference, BMI, and blood pressure readings. (7)

Xenical vs. Phentermine: A Side-by-Side Comparison

Although both Xenical and phentermine are types of weight loss medication, their side effects, warnings, and mechanisms for prompting weight loss are very different.

The following table makes it easy to see the benefits and drawbacks of Xenical compared to phentermine.

Can You Take Xenical and Phentermine Together?

Taking a combination of Xenical and phentermine shouldn’t cause a problem, as the two weight loss medicines are not known to interact with each other.

However, it is commonly recommended that only one weight loss drug be taken at a time unless prescribed by your doctor. This may help to reduce side effects or the occurrence of an unexpected drug interaction. (15)

Phentermine or Xenical – Which One Is Better for Me?

When comparing phentermine vs. Xenical, the better drug will depend on your medical history and the type of diet you are willing to follow while taking the pills.

Phentermine might be considered the more convenient drug, as only one capsule is taken each day, whereas Xenical must be taken with each fat-containing meal. Xenical is also the more expensive weight loss medication.

Although both drugs have been proven to aid weight loss in clinical trials, their mechanisms of action are different. Xenical prevents a proportion of dietary fat from being absorbed, whereas phentermine stimulates the central nervous system to boost energy and reduce appetite.

Xenical can cause unpleasant side effects in the bowel, especially if too much fat is consumed. Phentermine’s side effects include headaches, dry mouth, and insomnia. Xenical has fewer warnings for use than phentermine, but it is important to familiarize yourself with the manufacturer’s guidance prior to use.

To ensure you choose the most appropriate treatment plan, and the drug that will give you the highest chance of weight loss success, speak to your doctor before commencing medication.