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The Real Scoop on Orlistat Side Effects

The Real Scoop on Orlistat Side Effects
Dr. Constance Odom, MD Picture of Dr. Constance Odom, MD

Medically reviewed by

Written by our editorial team.

Last Edited 6 min read

Orlistat is a weight loss drug sold under the prescription name Xenical and over-the-counter as Alli. When it first hit the market, it was revolutionary because it had FDA approval.

As with any government-approved medication, orlistat had warnings about side effects. However, users did not take them as seriously as they should. What they soon learned about the long term side effects of orlistat is that they were embarrassing and inconvenient.

Before you write off this medication, though, take time to learn a bit more about the side effects. You'll discover that you can control them and possibly avoid them completely.

List of Orlistat Side Effects

WebMD outlines different categories of orlistat side effects. Some are short-term issues while others are the long term side effects of orlistat. You will see that the more common issues are those that are not long-lasting.

Most Common

Most people will experience some or all of these side effects when they start using orlistat:

  • Uncontrollable bowel movements
  • Discharge when passing gas
  • Anal leakage
  • Stomach pain
  • Loose stools
  • Oily discharge
  • Increase in bowel movements
  • Low levels of vitamin D

Less Common

These side effects may not always occur in users of the medication:

  • Cold symptoms
  • Gallstones
  • Low vitamin A levels
  • Dizziness
  • Low vitamin E levels
  • Anxiety
  • Tooth problems
  • Gum disease
  • Headaches
  • Rectal irritation
  • Low energy

Severe Reactions

If you experience any of these side effects, you should seek medical treatment right away:

  • Allergic reaction
  • liver problems
  • Stomach or intestinal bleeding
  • Kidney stones
  • Low blood sugar

Severe reactions often occur over a period of time. You may require continuous monitoring to ensure they do not happen. Your doctor may advise continuous monitoring if you have risk factors or a medical history of liver, kidney, or stomach problems or chronic health issues, such as high blood pressure or diabetes.


These side effects are not common but have occurred in at least one user of orlistat:

  • Urinary tract infection
  • Bronchospasm
  • Hives
  • Middle ear infection
  • Arthritis
  • Itching
  • Vaginal inflammation
  • Water retention
  • Abdominal swelling
  • Menstruation issues

You should seek medical attention if you experience any of these and think they may be due to using orlistat. Your doctor may want to monitor you to see if these are effects of the medication.

Why Side Effects Occur

In general, orlistat is a safe medication. There is no known overdose risk, and there are typically no long term side effects of orlistat. Avoiding such issues is usually easy when you go through a proper screening with your doctor when trying to see if orlistat is right for you.

However, most people who use this drug will experience some side effects in at least the first few days or weeks because of the nature of the medication. Orlistat blocks the absorption of fat in the intestine. When you eat food, the intestine will usually absorb and use the fat, but when you take orlistat, it cannot do this, so it must get rid of the fat in some other way.

Your body will expel this through bowel movements. It can irritate your bowels, leading to the common side effects.

Orlistat also blocks the absorption of vitamins, minerals, and nutrients from the food you eat. This also causes side effects with low vitamin levels or getting proper nutrition.

In some people, the change orlistat makes in the intestines can lead to issues with other organs, which would result in the rare side effects.

There is also a risk with taking any medication that you could suffer an allergic reaction. Your body could see orlistat as an allergen and attack it, leading to a severe allergic reaction.

How To Prevent Side Effects

Obviously, you want to avoid any short or long term side effects of orlistat. The most common issues are fairly easy to avoid once you settle into taking the medication on a regular basis. You may also be able to minimize the initial issues you have when you begin taking the medication by taking specific steps.

The Mayo Clinic explains that you must use the medication in the way directed by your doctor. Listen to all instructions you receive. The most important point is that your diet cannot be more than 30% fat.

You need to spread this fat out between three meals each day. You must take the medication with each meal because it works only on that meal. You also need to take the proper dose, which is one pill with each meal, three times per day.

To avoid issues with vitamin deficiencies, you should take a daily vitamin. However, you should never take your vitamin or any other medication within two hours before or after taking orlistat.

Keep in mind that when you first start using the medication, your body must adjust to it, so you will experience some side effects. However, these tips can help to minimize them and make them more manageable so that you do not experience embarrassing issues. The problems should go away after you continue to regularly use orlistat.

What To Do When Side Effects Occur

Whether you have initial issues or suffer from the long term side effects of orlistat, it is likely that you want to know how to cope with them. The first thing you should do is keep taking the medication so that your body can adjust.

However, you also need to pay attention to what is happening. If your symptoms get worse or do not appear to be clearing up, you should contact your doctor. If you experience something beyond the common side effects, you should also let your doctor know as they may indicate a more serious issue.

The best way to deal with side effects is to be more careful with your diet. You need to maintain the 30% fat ratio in your diet. It also will help to avoid bad fats, such as fried foods. Instead, make the fats in your diet healthy, such as that in olive oil and nuts.

Also, remember that orlistat works on the meal with which you take it and about 2 hours after. Use this to help you plan "cheat meals" and avoid side effects.

As you adjust to using the medication, consider wearing dark pants and carrying an extra pair of clothes with you when away from home. You may also want to use pads or diapers if you are having uncontrollable bowel issues.

The Bottom Line

For most people, the long term side effects of orlistat are embarrassing on occasion but nothing too severe to make them stop using the medication. Since side effects typically go away within a few weeks of using the drug, most people feel they can easily put up with them for the benefit of enhanced weight loss.

If you have side effects when using this medication, you can always discuss them with your doctor, and you should do this if your side effects are causing you issues in your daily life. Common side effects are usually nothing to worry about, but if you have issues that are severe or rare, then you need to seek medical care to ensure there is nothing more serious going on.

The bottom line is that almost everyone experiences side effects from taking orlistat. However, most people can control them by watching their diet and fat intake without them becoming too intrusive or making them want to stop taking this diet medication.

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This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your physician about the risks and benefits of any treatment. Nu Image Medical may not offer the medications or services mentioned in this article.