Orlistat Side Effects, Uses, and Drug Interactions

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Orlistat has gained popularity because it is very effective in helping people shed pounds and maintain their weight once they’ve achieved their goals.

However, like many other medications, orlistat can cause certain side effects. Most of the side effects of orlistat are caused by its impact on the digestive system.

Although unpleasant, these gastrointestinal side effects often mean the drug is working as it should.

In this article, we discuss the mild-to-moderate and more severe side effects you may experience while taking orlistat.

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What is Orlistat?

While orlistat is often prescribed by healthcare professionals, it can also be obtained over-the-counter (OTC) at pharmacies.

Orlistat can improve your weight loss results, but those taking it shouldn’t rely on the medication alone to lose weight.

This drug should be used with a weight management program that includes a balanced diet and physical activity.

How Does Orlistat Work?

The medication works by inhibiting the activity of enzymes in the digestive system called lipases.

Lipases are responsible for breaking down dietary fat so that the body can absorb it.

Orlistat prevents some of the fat that you eat from being broken down and absorbed. This means that fewer calories are absorbed into the body from the fat you eat.

The unabsorbed fat is excreted from the body in the stool.

What is Orlistat Used for?

Orlistat is typically prescribed to individuals who have been unsuccessful in their attempts to lose excess weight through diet and exercise.

The drug can also be used to prevent weight gain once you’ve achieved your weight loss goals.

It is also often prescribed to people with chronic conditions such as high blood pressure (hypertension), diabetes, high cholesterol, or heart disease who need to lose weight to manage their disease.

Common Orlistat Side Effects

The most common side effects of orlistat are caused by its effect on the digestive system described above.

If the side effects outlined below affect your quality of life or become bothersome, contact your doctor for medical advice.

They may make adjustments to your orlistat dose to reduce side effects or prescribe an alternative medication.

Some of the more common side effects of orlistat include:

Oily stools

As a portion of the dietary fat you consume is not broken down and absorbed, it can result in oily stools or oily discharge. The unabsorbed fat can give stools a greasy appearance.

Although this side effect may be unpleasant, it’s typically a sign that the medication is working effectively to interrupt the activity of lipases in the body.

Pale stools

The brown color of stools is usually the result of bilirubin, which is a waste product caused by the breakdown of old red blood cells.

Bilirubin is typically processed by the liver, released into the digestive system, and then excreted via stool.

As orlistat interferes with the absorption of consumed fat, it can reduce the amount of bilirubin in the stool, which may make it look paler than usual.

Increased bowel movements

Individuals who take orlistat will have some unabsorbed fat in their digestive system, which can lead to changes in bowel habits – including increased movements.

This happens because the body is trying to eliminate excess fat through stool.

Abdominal pain or discomfort

As a result of orlistat’s impact on the digestive system, some people report abdominal pain or discomfort.

Having undigested fat present in the intestines can also cause uncomfortable bloating.

Digestive problems

Other than the digestive symptoms described above, orlistat may also cause diarrhea as well as nausea and vomiting. There are three potential reasons why people may experience this side effect:

  • Gastrointestinal disturbance: The undigested fat that is present in the digestive system can cause an upset stomach.

  • Dietary fat intake: Consuming high-fat meals while taking orlistat can worsen digestive issues.

  • Sensitivity: Some people might be particularly sensitive to the changes in fat absorption that orlistat causes in the body, which makes them feel ill.


Although not as common as the gastrointestinal side effects of this medication, some people may experience headaches when taking orlistat.

It’s not fully understood why headaches occur with orlistat, but here are three potential explanations:

  • Dehydration: Increased bowel movements and diarrhea can lead to dehydration, which triggers headaches.

  • Sensitivity to orlistat: Everyone responds to medications differently, and some people may be more sensitive to orlistat than others, making them more prone to headaches.

  • Changes in diet: Most people taking orlistat are advised by their health care provider to follow a low-fat meal plan. This dietary change as well as a lower calorie intake could lead to headaches.

Low blood sugar

Although research shows that orlistat is effective in regulating blood sugar levels, it may cause problems for people with diabetes.

Individuals with type 2 diabetes, in particular, may experience low blood sugar (hypoglycemia) due to the changes in their bowel habits when taking orlistat.

Symptoms of hypoglycemia include:

  • Dizziness
  • Shaking
  • Extreme hunger
  • Confusion
  • Sweating


If people taking orlistat eat high-fat foods, incontinence may occur. The digestive changes that orlistat causes can result in the extreme urge to pass stool (fecal urgency). This could lead to accidental bowel leakage.

Serious Orlistat Side Effects

Aside from the more common side effects listed above, there are some more serious adverse effects people may experience when taking orlistat.

An unusual or allergic reaction

While allergic reactions to orlistat are very rare, they can be serious. Symptoms of an allergic reaction include:

  • Trouble breathing
  • A rash, redness, or inflammation of the skin
  • Severe dizziness or fainting
  • Swelling of the mouth, lips, throat, and tongue
  • Severe abdominal pain

Kidney stones

This is another rare side effect that people taking orlistat may experience.

The association between this drug and kidney stones is not completely understood, however, it could be due to calcium and oxalate excretion.

The changes in metabolism caused by orlistat can influence the levels of calcium and oxalate in the urine. Elevated concentrations of these substances can increase the risk of kidney stone formation.

Symptoms of kidney stones include:

  • Bloody or dark urine
  • Severe back or abdominal pain
  • Frequent urination

Liver injury

Research shows that orlistat may cause severe liver symptoms, including inflammation, in rare cases.

Symptoms of liver injury include:

  • Yellowing of the skin
  • Dark urine
  • Extreme fatigue
  • Severe abdominal pain

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When to Call Your Doctor About Side Effects

It’s vital to call your doctor immediately if you suspect you are experiencing one of the serious side effects mentioned above.

They may need to adjust your orlistat dose, or you may need to discontinue the medication entirely.

You must also seek immediate medical attention as these adverse effects may be life-threatening.

Key Point: Orlistat Overdose

If you think you’ve taken too much orlistat, you should contact a poison control center and visit an emergency room right away.

Drug Interactions with Orlistat

A drug interaction is when other medicines or substances interfere with how a medication works.

While a health care professional can advise on what interacts with orlistat, here are the main known interactions:

  • Blood thinners such as warfarin
  • HIV medications such as atazanavir, efavirenz, emtricitabine, lopinavir, tenofovir
  • Seizure medications
  • Fat-soluble vitamins

Brand Names of Orlistat

Orlistat can be found in the following medication brands:

  • Alli
  • Xenical

Precautions When Taking Orlistat

If you are taking orlistat, there are some precautions you should follow.

Stick to a regular dosing schedule

Orlistat is effective when it is taken at the same time each day so that it can consistently inhibit the absorption of dietary fat.

In the event that you forget to take your orlistat, take the missed dose as soon as you remember it, unless it’s more than one hour since you ate a meal.

If it’s been more than an hour since you last ate, skip the missed dose.

Don’t share your medication with anyone else

Never share your orlistat with anyone else, especially people with eating disorders. This is not a one-size-fits-all medication, and people may have adverse reactions to the drug.

Take orlistat with food

Orlistat is known to be most effective when it is taken with a main meal. It specifically targets the fat in that meal and reduces its absorption into the body.

Taking the drug with food may also help to minimize gastrointestinal-related side effects.

Avoid foods high in fat

Eating high-fat foods while taking orlistat may worsen the potential for the side effects explained above.

What to Tell Your Doctor Before Taking Orlistat

If you are thinking about taking orlistat, you must be completely transparent with your healthcare provider about any medical conditions that you have, as well as any medications — including herbal products — that you are taking.

  • You should tell your doctor if you:
  • Have an eating disorder or a history with disordered eating
  • Have a history of liver disease
  • Have malabsorption syndrome
  • Are pregnant, planning on conceiving, or breastfeeding

How to Maintain a Reduced Calorie Diet While Taking Orlistat

As mentioned above, orlistat is intended for use in conjunction with a healthy diet and exercise program.

Research shows that when orlistat is combined with regular exercise and a balanced diet, it can help most people lose significant amounts of weight.

Physical activity

According to the Centers for Disease Control and Prevention (CDC), adults should get 150 minutes of moderate-intensity physical activity each week. You can break this up into 30 minutes a day for five days.

Examples of moderate-intensity exercise include:

  • A brisk walk
  • Swimming
  • Yoga

Healthy eating

Your doctor may have certain recommendations on how you should adjust your diet while taking orlistat.

It is generally advised that no more than 30% of the calories you consume should come from fat while taking this drug.

Where Can I Learn More About Orlistat?

Through LifeMD, you can speak to a board-certified physician or nurse practitioner about taking orlistat.

A healthcare professional can answer any questions you have about the drug and provide you with a prescription, if necessary.

If you find that orlistat is not right for you, ask your doctor about LifeMD’s Weight Management Program. This comprehensive program is an interactive weight loss journey with you and your healthcare provider where you may be prescribed medication in conjunction with clinical oversight, metabolic testing, and ongoing support from your doctor to help you lose weight and feel healthier overall.

Head over to the LifeMD website to make an online appointment today.

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This article is intended for informational purposes only and should not be considered medical advice. Consult a healthcare professional or call a doctor in the case of a medical emergency.

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