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Alli vs. Xenical: What's The Difference?

<p>Alli vs. Xenical: What's The Difference?</p>
Dr. Constance Odom, MD Picture of Dr. Constance Odom, MD

Medically reviewed by

Written by our editorial team.

Last Edited 4 min read

Being excessively overweight is more than an issue of not fitting into clothes or losing aesthetic appeal. It is a battle that has to be fought for a healthier future free of the restraints of excess pounds and the health complications it brings. 

Obesity and other conditions that fuel excessive weight gain are fast becoming a pandemic in their own right. The World Health Organization states that the obesity prevalence rate has nearly tripled since the 1970s.

Presently, over 500 million adults, children, and adolescents are diagnosed as clinically overweight or obese. Considering that these weight conditions can lead to near or sudden death, effective measures must be taken to manage weight gain and promote weight loss. 

Weight loss or anti-obesity drugs such as Alli and Xenical are two of the most accessible options available for this condition. These two synthetic drugs use a non-traditional approach to stop fat accumulation. Since these two drugs have the same goal, what sets them apart?

Below we expand on just that and find out a bit more about these treatments:

Alli and Xenical in a Nutshell

  • Alli 

Alli is a weight loss drug created by GlaxoSmithKline, a pharmaceutical manufacturer that has quite a few medicinal wonders under its belt. Alli uses the active ingredient orlistat to induce weight loss and comes in a 60mg tablet. The numbers refer to how much orlistat is in the tablet.

In 1999 the active ingredient orlistat was FDA-approved as a prescription weight-loss drug that can be used with a controlled diet and increased exercise to treat obesity. The potent formula was also confirmed to lower the risk of re-gaining weight after prior weight loss, making it a weight management aid as well. 

But it was only in 2007 orlistat 60mg—Alli was approved for over-the-counter (OTC) distribution to induce weight loss in overweight adults. The active ingredient in this treatment aims to eliminate fat through excretory processes, which is quite conservative compared to invasive measures, such as surgery used to treat obesity.

Alli is both safe and effective and has produced excellent results over the years. Combined with a reduced calorie, low-fat diet, and moderate exercise, Alli can help users lose 50% more weight than just exercising and dieting alone.

Studies confirm this with clinical evidence that states orlistat 60mg produces clinically beneficial changes in body composition and disease risk factors when used in conjunction with an altered lifestyle. Simply put, it supports weight loss and eliminates the possibility of users developing conditions such as cardiovascular issues or diabetes.  

  • Xenical

Xenical is an FDA-approved oral weight loss treatment that was introduced to the market in 1999. The product was created by Cheplapharm, a family-owned pharmaceutical company globally recognized for its medicinal inventions. Like Alli, Xenical uses the active ingredient orlistat to support weight loss in individuals with obesity or other weight-related medical conditions.

The treatment has a high volume—120mg of the active ingredient orlistat, which means it can't be bought over the counter and is available on a prescription basis only. Despite its potency, the drug is very flexible and safe. Xenical can be used with other medicines and conditions, such as high blood pressure, a condition commonly associated with weight issues.

The drug has a proven safety and efficacy profile which, like Alli, means that its effects have scientific backing. It can also be used to initiate weight loss or maintain it, an effect that suffices as a dual use. This is quite a comforting thought, especially when dealing with sensitive issues such as weight loss. 

PubMed study showed that the drug produced excellent results when used with therapeutic lifestyle changes such as a beneficial diet and increased activity or exercise. Xenical can also be used both long and short-term without worrying about adversities.

Scientific evidence from a year-long study suggests that the treatment is an effective and safe solution for extended use. One-third of the patients in the trial achieved clinically relevant weight loss (more than 5% of their initial body weight). 

Is there a Difference in How Alli and Xenical Work?

The key to understanding how any treatment works lies in the active ingredient it uses to carry out its function. Since Alli and Xenical use the same active ingredient—orlistat, their mechanism of action or how they work is the same.  

Alli and Xenical belong to the same class of medicine called gastrointestinal lipase inhibitors, more commonly referred to as fat blockers. Once Alli or Xenical is consumed, their active ingredient is gradually introduced into the bloodstream to block the function of lipase. The primary function of this enzyme is to break down and extract fat from food for storage.  

By stopping the function of this enzyme, these drugs prevent the body from absorbing large amounts of fat, leading to fat loss. The agent also extracts different types of fat found in the liver and abdomen, further promoting weight loss and lowering fat ratios. 

Eliminating liver and abdominal fat also benefits users' overall health. Studies show that those with obesity and/or related conditions are at risk of developing health issues due to the presence of liver and abdominal fat. All the unwanted, unhealthy fat is moved out of the body naturally through fecal excretion—bowel emptying. This is quite a simple yet effective technique for fat elimination. 

Alli and Xenical Safety/Efficacy

The effectiveness and safety of a drug is not only a concept that interests professionals and industry experts but also us as patients as well. It tells us how well a drug performs its function and how safe it is for use. It gives patients both hope and peace of mind about their diagnosis. 

When it comes to weight-related medical conditions or situations where weight loss interventions are futile, the efficacy and safety of possible solutions, like Alli and Xenical, are constantly evaluated. According to their respective manufacturers, both these drugs are safe and effective. 

Below we see what clinical trials and studies have to say about this:

  • Alli

-A clinical trial focused on the effectiveness of Alli found that the drug helped individuals successfully lose 10% of their total weight to qualify for bariatric surgery. The weight loss took place in the stipulated time frame, and mild gastrointestinal side effects were experienced by a small group of users. 

-Another study showed that weight loss induced by Alli also showed improvements in blood sugar, blood lipid levels, and blood pressure, which reduces the risk of developing diabetes.  

  • Xenical

- A study looking at the effect of Orlistat on sterol metabolism in obese patients showed that the treatment increases overall metabolism, and it plays an important role in preventing coronary artery disease through these processes. 

-A trial evaluating the effectiveness of Xenical found that the treatment does reduce weight, helping users reach their BMI in desired timeframes. Users also saw an improvement in waist circumferences and body composition. Mild, short-lived GI side effects like loose stools, oily stools, abdominal pain, and fecal urgency were recorded.

The trials and studies confirm manufacturer claims. These drugs are indeed safe and effective in their own right. Xenical is slightly more potent, but this aligns with the patient group it was designed to treat.

Usage, Dosage, and Strength Explained

When it comes to usage, dosage, and strength, Alli and Xenical differ slightly. As we mentioned earlier, Alli tablets come in  60mg, while Xenical is available in 120mg. The strength variation caters to different user groups within the overweight and disordered eating community. 

Alli is available over the counter for adults who are overweight according to their BMI. It can also be used in mild obesity cases with no complexities. Xenical, on the other hand, is available on a prescription basis only to treat obesity and weight-related medical issues. 

The recommended frequency of dosing is the same for Alli and Xenical. Both manufacturers suggest taking a single tablet 3 times daily, with each main meal containing fat. The tablet can be taken during a full meal or up to 1 hour after a meal. 

All meals should be nutritionally balanced, low in fat and calories. However, 30% of the calories must come from fat. When using Alli or Xenical, users should not skip meals. Eating small healthy meals regularly is encouraged.  

Experts suggest taking a multivitamin containing fat-soluble vitamins such as vitamins A, D, E, K & beta carotene once at night/bedtime to bridge the nutritional gaps these drugs may cause. Since Alli and Xenical reduce fat absorption, they may also affect the absorption of fat-soluble vitamins.

Both drugs can be used as a weight loss and weight management aid however, Xenical comes in with more flexibility of use due to its higher concentration/volume of orlistat. Xenical is more frequently linked to successful use in combination treatment plans or circumstances involving disordered eating and other ailments. 

Alli, on the other hand, doesn't fare well in combination treatment plans. The difference in flexibility can be attributed to the inactive ingredients or how the ingredients are blended together. It can also be due to the drug's response to different user lifestyles, body types, and composition. 

Alli vs. Xenical Side Effects 

Alli and Xenical are considered safe and tolerable because they do not directly affect the central nervous system and the heart. This is primarily because the active component is not fully absorbed into the bloodstream and has no cumulative effect on the body. 

Since the effects of each dose do not linger in the body, the possibility of side effects is lower compared to other anti-obesity medications. Although the chance of experiencing side effects is low, it's not impossible, which means acknowledging and understanding them is imperative. 

The side effects linked to the use of these drugs can be very unpleasant and uncomfortable, but most experts suggest pushing through them as their presence is short-lived. Because the active ingredient in both medicines is the same, the type of side effects experienced is also the same. 

Let's look at the common side effects below:

  • Fecal spotting, diarrhea

  • Frequent urge to empty bowels 

  • Abdominal pain, and anal fissures

  • Oily stool/discharge and excess flatulence 

  • Inability to control bowel movements or loose stools

The difference here comes in the frequency and intensity of side effects. Those using Xenical have a higher chance of experiencing side effects at a greater intensity because it has a higher volume of the active ingredient.

Contraindications and Interactions

Contraindications are situations or health conditions that do not allow the use of a specific medicine, while interactions refer to substances or medicines that cannot be used together. Alli and Xenical have the same contraindication and interaction list due to their similar composition. Below we give you a quick overview of this contraindication and interaction list:


  • Bulimia

  • Pregnancy

  • Anorexia nervosa

  • Blockage of normal bile flow

  • Abnormal liver function tests

  • Calcium oxalate kidney stones

  • A high volume of oxalic acid in urine

  • Damage to the liver and inflammation

  • A condition with low thyroid hormone levels

  • Abnormal absorption of food nutrients in the gastrointestinal tract


  • Concomitant cyclosporine

  • Anticoagulants 

  • Amiodarone

  • Antidiabetics

  • Antiepileptics

  • Antiretrovirals

  • Thyroid drugs

  • Other weight loss products

The Bottom Line

Alli and Xenical are undeniably effective weight loss aids/anti-obesity drugs that can provide noticeable results to those who are overweight or suffering from disordered eating. These treatment options break the shackles of traditional fat burners that use appetite suppression as their core approach.

Instead, Alli and Xenical venture directly to the source of the problem, which is fat. They essentially block fat absorption and stop fat storage, serving the holistic goal of weight loss. The differences between these treatments are slight and noted below:

  • Alli can be purchased over the counter without a prescription. Xenical, on the other hand, requires a prescription.

  • Alli is most effective when used for those struggling with weight issues or who are overweight, while Xenical is better suited to those diagnosed with disordered eating like obesity or conditions that fuel weight gain.

  • Xenical can be safely used in patients who have underlying conditions or conditions associated with disordered eating. Alli cannot be used in such cases and is only recommended for straightforward cases.

  • Alli and Xenical have different dosages and potencies. Alli is available in 60mg strength/dose, and Xenical comes in a 120mg strength/dose.

  • Alli comes with a starter kit with a step-by-step guide that tells users how to effectively use the drug in conjunction with a weight loss plan (diet and exercise regimen). Xenical doesn't come with additional support. 

These differences do not affect the individual safety or efficacy of either product. It simply helps users decide which product best suits their needs, lifestyles, and conditions. 


9 Sources

Nu Image Medical has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

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.