How to Lose Weight Using Orlistat

by Ahmed Zayed, MD on January 23, 2019
Last updated on May 23, 2021

Prevalence of overweight and obesity is on the rise across the globe, particularly in developed nations. According to the CDC, about 93.3 million adults or 39.8% of this population in the United States is obese. Prevalence of obesity among young adults is around 35.7%, middle-aged adults about 42.8%, and older adults about 41% (1). Regardless of how much weight a person has gained, it’s possible to slim down with hard work and well-structured plan.

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Doctors may prescribe weight loss pills to their obese patients to kick-start the process. Orlistat is one of those pills. Does it really work and what are its mechanisms? Throughout this article about orlistat for weight loss, you’ll get the answer to that and other questions regarding this pill.

What Is Orlistat?

Orlistat is a drug specifically created to treat obesity. It is used together with behavior change, reduced calorie diet, and doctor-approved exercise to help users slim down.

The goal is to enable men and women to start losing weight, but it is not a miracle pill, i.e. its use needs to be accompanied by the above-mentioned lifestyle modifications. Orlistat is recommended to certain overweight persons such as those who are obese or have weight-related medical problems. In addition, the drug supports weight management by preventing users from gaining pounds they have already lost. Orlistat is marketed under two brand names: a prescription-only drug Xenical and an over-the-counter weight loss medication Alli. Both forms of the drug are FDA-approved. Xenical was approved by FDA in 1999 for obesity management in conjunction with necessary lifestyle modifications.

On the other hand, Alli was approved in 2007 for weight loss in overweight adults ages 18 and older in conjunction with low-fat and reduced-calorie diet (2). The primary difference between Xenical and Alli is that prescription-only drug contains 120 mg orlistat while the latter has a lower strength of only 60 mg orlistat.

How Does Orlistat Work?

This drug works by blocking pancreatic lipase, enzymes which digest fat in the gut. In other words, orlistat blocks some of the fat that you consume thus keeping it from being absorbed by the body. Orlistat can block about one-third of fat that you eat (3). So, what happens with it? Undigested fat, i.e., fat that isn’t absorbed by the body, is passed out in feces (stool) (4). Bearing in mind that dietary fats need to be broken down into smaller pieces before they are absorbed by the body, the primary mechanism of action of orlistat is to block this activity. As a result, it can tackle the accumulation of lipids in fat storage and help you slim down or manage your weight.

That being said, it’s important to mention that the drug does not block absorption of calories from sugars and other non-fat sources. Since it only tackles fat, you do need to follow doctor’s instructions regarding lifestyle changes such as calorie-reduced diet and regular physical activity.

Is Orlistat Effective?

Now that you know the mechanism of action of orlistat for weight loss it’s useful to address its efficacy. Does it really work or not? According to science – yes it does. For example, a review of evidence on this subject from the Vascular Health and Risk Management found that orlistat is associated with small, but significant weight loss of around 3% more than diet alone in overweight and obese people. Scientists also reported that taking 120mg orlistat three times a day resulted in 2.7kg or 2.9% greater weight loss compared to placebo. Pooled results revealed a larger number of subjects in the orlistat group achieved clinically significant weight loss with 21% and 12% experiencing ≥5% and ≥10% weight loss respectively. In addition, participants who took orlistat also experienced reductions in waist circumference ranging from 0.7 to 3.4cm.

The review also showed that some subjects have a more dramatic weight loss than others when taking orlistat. Interestingly, the drug is cost-effective only in situations when a person achieves at least 5% weight loss in three months of the regular use of this medication. Good news is that weight loss is generally maintained in persons who take orlistat. This means that losing weight and keeping it off is not some silly claim, but a true fact. Yet another proof of orlistat’s efficacy, the above-mentioned review reports, is that it can lower the risk of potentially severe health conditions associated with obesity.

For example, over four years of orlistat treatment in one study decreased the risk of diabetes by 37.3% compared to placebo. Patients taking orlistat also show improvements in blood pressure and serum cholesterol levels (5). A different study, published in the Indian Journal of Endocrinology and Metabolism, also confirmed that orlistat caused a significant reduction in weight, BMI, waist circumference, cholesterol, and LDL level. Scientists concluded the drug is effective and well-tolerated for anti-obesity purposes and it can be employed as an adjunct to therapeutic lifestyle changes to achieve and maintain optimal weight (6).

Besides the evident effects on body weight and decreased risk of diabetes and cardiovascular diseases, the use of orlistat can help improve fertility in women.

One study discovered that orlistat improves ovulation in women treated for obesity (7). Better ovulation is a result of weight reduction. This is particularly important if we bear in mind that overweight and obesity have a negative influence on fertility and many women with excess weight struggle to conceive. It’s definitely a good thing that orlistat can help promote ovulation which is vital for fertility and pregnancy.

To women who have been struggling with fertility, this is a glimpse of hope that they will be able to conceive and have a baby. Of course, if you’re having fertility problems, you should consult your doctor and see what they would recommend for a successful conception.

When Is Orlistat Prescribed?

Above in the article, we already mentioned that orlistat is specifically created to help persons who are overweight or obese. But, who is eligible for a prescription pill (Xenical)? It’s important to bear in mind that orlistat isn’t easily given to every person who wants to slim down. The drug is only recommended to persons who have a certain BMI. Before the doctor prescribes orlistat, he will make sure that you intend to change diet and physical activity levels.

In other words, the physician wants to be certain that you’ll use the drug only as an adjunct to lifestyle modifications rather than taking the pill only without making any changes whatsoever. Prescription for orlistat is usually given to persons whose BMI is 30 or above. It can also be issued to a person whose BMI is 27 or 28 and above but who also has a medical condition that would benefit from losing weight. To continue the treatment with orlistat a person must lose at least 5% of their weight in three months. Otherwise, the treatment is stopped. On the other hand, Alli or the over-the-counter form of orlistat is approved for use in adults 18 and older who have BMI 25 or higher. Even though you don’t need a prescription for this drug, it’s still useful to consult your doctor about it, particularly if you have some underlying health problems too or if you’re taking some medications.

What Is The Dosage?

To get the most out of orlistat for weight loss it’s vital to stick to the dosage recommended by the manufacturer or prescribed by your physician. Xenical, prescription-strength orlistat, is taken orally three times a day with each main meal containing fat. The same dosage instructions apply to Alli or OTC orlistat, just in this case dosage is 60 mg instead of 120mg. Orlistat should be taken during or up to one hour after meals.

You may skip the dose if the meal is skipped or it doesn’t contain fat. Of course, it’s crucial to have a well-balanced diet which involves eating all meals without skipping and moderate consumption of different nutrients including fat. Your meal should contain no more than 30% fat. While it may seem that taking more than prescribed, e.g., dosages higher than 120mg could lead to greater weight loss that’s not correct (8). That’s why it’s crucial to stick to the dose that was proven to be effective and also recommended by your doctor. In addition, fat content in total daily caloric intake should not be higher than 30%. For instance, if you consume 1200 calories a day the number of calories from fat shouldn’t be higher than 360.

Keep in mind that the drug was created to aid weight loss in combination with other lifestyle measures so make sure you don’t rely on it like it’s some sort of a miracle pill. Due to the fact that orlistat may make it more difficult for the body to absorb some vitamins and minerals you may need to consult the doctor about taking supplements while on the treatment.

Side Effects of Orlistat

Journal of Obesity published a study which found that differences in weight loss results among subjects treated with orlistat could be down to lack of adherence. Some people have significant weight reduction while others who are on the same treatment don’t. They found that uncomfortable side effects associated with this drug could be a reason why some people don’t adhere to orlistat properly (9).

The most common side effects are caused by fat which passes in the stool. For example, some patients may experience adverse reactions such as fatty smelly stools, oily spotting in underwear, excess wind, and urgency to go to the toilet. Although uncomfortable these side effects tend to go away after a while. Also, if you eat more fat than you should these adverse reactions may get worse so always stick to the recommended fat intake. Some other side effects associated with orlistat include:

  • Bladder pain
  • Headache
  • Loss of appetite
  • Nausea
  • Sweating
  • Vomiting
  • Trouble sleeping
  • Runny nose

Serious allergic reactions to the drug are rare, but if you have symptoms such as rash, itching/swelling, dizziness, and trouble breathing seek medical help. You should also get emergency help if you display symptoms of liver disease (persistent nausea, vomiting, severe stomach pain, dark urine, and yellowish skin/eyes) and symptoms of kidney stones.

Who Shouldn’t Use Orlistat?

As much as orlistat is effective, it’s not suitable for everyone. You should avoid taking orlistat in the following situations:

  • Pregnancy and breastfeeding
  • Chronic malabsorption syndrome
  • Cholestasis

You should inform your doctor before asking prescription for orlistat if you have (or have had) the following problems:

  • Hypothyroidism
  • Kidney stones
  • Gallbladder disease
  • An eating disorder such as bulimia and anorexia
  • Kidney disease
  • Liver disease
  • Pancreatitis

Bear in mind that orlistat interacts with certain medications such as blood thinners (e.g., warfarin), HIV medications, hypothyroidism medications, antiepileptic drugs, and others. Inform your doctor about medications you’re taking before getting a prescription for orlistat or buying it in OTC form.


Orlistat is a common weight loss medication available in prescription and OTC strength. Evidence confirms the drug promotes weight loss, decreases the risk of diabetes and cardiovascular diseases, improves fertility in women, and supports weight management. Orlistat is created to act as a supporting act to the star of the show which is a calorie-reduced diet and regular exercise.


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