How Does Orlistat Work?

Orlistat is a prescription-only weight loss treatment in the form of an oral tablet or capsule. It is the generic version of the branded alli and Xenical medications. This means it contains the same active ingredient as alli and Xenical, the only difference is their price and packaging.

Clinical research has shown that 37% of people lose 5% or more of their starting weight after just 12 weeks of taking 120mg orlistat.

Recent studies also found that between 50 and 80% of patients taking orlistat between 6 to 12 months maintained a loss of 5% or more of their starting weight alongside lifestyle changes such as exercise routines and a healthy diet.

You should start to see results from taking orlistat between 1 to 3 months of taking it. Orlistat affects people differently and patients will see different results depending on their circumstances and diet plan.

Your doctor will advise the best plan for you with orlistat, including the correct lifestyle changes to take alongside your treatment with orlistat.

Orlistat vs Wegovy vs Mounjaro vs Mysimba vs Saxenda

It’s good to know all the facts before starting a weight loss treatment, so let’s look at the effectiveness of orlistat versus other weight loss treatments.

Studies have shown that orlistat helped 37% of people lose 5% or more of their starting weight after 12 weeks. To compare, when taking:

• Mysimba, patients lost an average of 8.1% of their starting weight after 56 weeks of treatment
• Wegovy patients lost up to 15% of their starting body weight on average when taking the 2.4 mg maintenance dose after 68 weeks
• Mounjaro patients lost up to 22.5% of their starting weight while taking the highest maintenance dose of 15 mg after 72 weeks
• Saxenda patients showed an average of 8% change in body weight after 56 weeks at the maintenance dose

Orlistat contains the active ingredient orlistat, which works to reduce the amount of fat that is absorbed into your body. It does this by binding to the fat in your food that you digest, which then prevents it from being able to be absorbed by your digestive system. This fat then passes through your body instead, and is removed through your stool when you go to the toilet. It does this for around a third of the fat you eat at each meal.

This helps you lose weight as you absorb less fat from the food you eat, meaning you take in fewer calories. This helps you lower the calories you’re eating on a daily basis, supporting weight loss.

How does orlistat affect your body?

Orlistat’s active ingredient, orlistat, is a lipase inhibitor and therefore works with the digestive enzyme lipase, preventing it from absorbing fat from the food that you eat before you go to the toilet and dispose of it.

As a result of this effect, you may experience changes in your bowel habits. Your stools (poo) might be fatty or oily. You may also experience:

• the urge to go to the toilet more often
• wind (flatulence)
• oily spotting
• stomach discomfort

Don’t worry, these changes are usually not serious and occur due to fats not being digested. These effects are typically increased if you eat a meal with high levels of fat.

“To minimise the side effects of orlistat on your body, we recommend adjusting your diet to ensure you are eating enough fruit and vegetables alongside a healthy balance of protein, fats and carbohydrates. Fat intake should be around 30% of your daily calories and split between the 3 meals you take orlistat with.” – Dr Brenda Nomann, Medical Editor.

You must always take orlistat as instructed by your doctor. They should guide you in the right direction and give you personalised advice about nutrition on your weight loss journey. For general advice, NHS Eatwell Guide provides some guidelines on calorie intake and nutrition.

Does orlistat burn existing fat?

No, orlistat does not burn existing fat. Orlistat works to block the absorption of the fat you consume from food. As you consume less calories from fat in combination with diet and exercise, your body will burn existing fat to make up the lost calories as you lose weight.

What happens if you take orlistat without eating?

Take each orlistat tablet with a meal. If you take orlistat without eating anything, you’re more at risk of experiencing side effects and your orlistat won’t work as it should. This is because orlistat only works when you eat food that contains fat.

You must take orlistat as prescribed and advised, if you have any questions or concerns about this, speak with your doctor.

Orlistat begins to start working as early as 24 to 48 hours after taking it.

In clinical studies, patients reported noticeable results within 12 weeks (3 months) of treatment. Within the time span of 12 weeks, 37% of patients taking orlistat alongside lifestyle changes reported losing at least 5% of their starting body weight, compared to 19% of placebo patients (patients who took false medication).

Out of these successful patients, 49% of them went on to lose 10% of their body weight after one year.

You should only take orlistat beyond 12 weeks (3 months) if you have lost at least 5% of your body weight in that time.

If you are concerned about how long you should take orlistat for, speak with your doctor.

How long does orlistat stay in your system?

How long orlistat stays in your system is directly linked to your digestive system. Orlistat should only stay in your system for between 12 to 72 hours after taking it.

Orlistat is a prescription-only medication. It is suitable and usually prescribed if you:

• have a BMI of 28 or more, in addition to other weight-related health conditions (such as type 2 diabetes)
• have a BMI of 30 or more

Orlistat warnings

You should only take and use orlistat as prescribed by your doctor. If you are thinking of taking orlistat you should tell your doctor if you have certain health conditions, and any relevant medical family history.

Before taking orlistat let your doctor know if you:

• have chronic malabsorption syndrome
• are breastfeeding
• are allergic to orlistat or any ingredients in the capsules
• have cholestasis (liver disorder)

Make sure your doctor is aware of any medications you are taking, have taken or are thinking of taking before you start orlistat. For example, if you:

• have high cholesterol and are taking medication for it
• have diabetes and are taking medication for it

It is important that you are safe during your weight loss treatment journey. If you have any concerns about warnings of taking orlistat, take a look at the patient information leaflet that should come with the medication.

Like with all medications, orlistat comes with side effects – although not everyone will experience them.

Common side effects of orlistat include:

• headache
• stomach ache
• flatulence (wind) with discharge
• oily discharge
• oily, liquidy, soft or fatty poo
• low blood sugar
• irregular period
• tiredness

If you are experiencing any of these side effects, they should improve with time. You should be able to manage them at home, such as eating less fat with each meal, resting and avoiding highly-processed foods.

Uncommon side effects of orlistat include:

• allergic reaction: itching, rash, elevated itchy skin patches that are red, difficulties in breathing
• nausea
• vomiting
• skin blistering
• bleeding from rectum
• yellowing skin and eyes
• dark coloured urine
• stomach pain
• loss of appetite

You can find more information on uncommon and rare side effects in the patient information leaflet.

If you have been affected by any of these side effects, and they are becoming persistent, bothersome, and are affecting your day to day life, speak with your doctor. They may advise you to stop taking orlistat and offer an alternative weight loss treatment.

When taking orlistat, it is important you take it correctly – 1 oral capsule 3 times a day with a drink of water and your meals. You must also follow the personalised guidance of your doctor.

An analysis of 4 clinical studies concluded that orlistat is most effective when taken alongside diet and exercise regimens. Following these requirements can also help to minimise potential side effects and help you lose more weight while on orlistat and in the future if you continue following these habits.

Eating well on orlistat

Orlistat’s active ingredient, also called orlistat, works with your digestive system to prevent your body from absorbing fat, which means a third of the fat from your food will be passed through to your stools (poo). Therefore, it is beneficial if you are eating a healthy, balanced diet to help orlistat work the best it can for you and your body.

A ‘healthy, balanced diet’ means:

• eating a diet low in fat
• eating fruit and vegetables
• eating a healthy portion of protein and carbohydrates
• avoiding ‘high fat’ foods (fried food, full fat food, super processed food)

Try and make sure that the amount of fat, protein and carbohydrates you eat is spread over 3 meals a day. This will also help orlistat work as you take it once with each meal.

Eating high-fat meals will increase side effects (such as stomach pain, wind and oily stool) due to the way orlistat prevents your body’s absorption of fat. If orlistat is exposed to too much fat, the medication will be less effective.

There are a range of free resources you can use to stay informed and track your eating habits:

• NHS EatWell Guide
• NHS calorie checker
• NHS food scanner

Orlistat does not burn fat, it works with your digestive system to prevent the absorption of it so that you can dispose of it in your stools.

Clinical studies have found that light exercise alongside taking orlistat can increase its effectiveness, even in short periods of treatment.

Due to the way orlistat works, we recommend exercising regularly to help burn fat during your treatment and stay healthy as you take the medication.

If you think orlistat is right for you, but you are unsure about where to start when it comes to exercise, visit NHS Exercise guidelines. These guidelines provide a range of how-to videos and physical activity information across ages and abilities.

Always speak with your doctor about your personal health condition and weight loss treatments you feel might be right for you. They will be able to advise the best course of action for your fitness needs.