How long does orlistat take to work?

If you’re looking for a medication that can help you on your weight loss journey, you may be curious about orlistat. Orlistat is a prescription drug available on the NHS and privately, to help people with weight management. It’s also sold over-the-counter at a lower dose, under the brand name Alli.

Unlike the newer crop of weight loss medications—GLP-receptor agonist drugs like Wegovy, Saxenda and Mounjaro —orlistat comes in pill form and doesn’t require any injections. It has also been around for quite a while, having been licensed for use in 1998. For a long time, it was the only drug available in the UK that was recommended for the management of obesity.

The drug, which works by blocking fat absorption in the digestive system, is not a substitute for a healthy lifestyle. And it isn’t a miracle drug—you’re unlikely to experience drastic weight loss. That said, it can give your weight loss journey an additional boost.

How does orlistat work?

Once you’ve taken a dose of orlistat, it travels to the gut, where it blocks the gastric and pancreatic lipases. These are enzymes (proteins) that help the body to break down fat. If lipase isn’t working properly, the fat will pass through your body undigested, eventually being passed out when you go to the loo.

Orlistat doesn’t stop all the fat you eat from being digested. Typically, you’ll absorb around 30% less fat than usual if you’re taking a typical dose (120mg three times a day with meals). Still, the impact can be significant, equivalent to cutting 200 extra calories every day.

This is a different mode of action from GLP-1 receptor agonists, which work by mimicking a hormone called GLP-1. Those drugs help keep you fuller for longer and curb your appetite, but they don’t have any impact on the way you digest fat.

How long does it take for orlistat to work?

Well, in one clinical trial, people taking orlistat lost 5.6kg (12.3lbs) on average over the course of six months, compared to 2.4kg (5.3lbs) for the control group. If that seems slow, bear in mind that super-fast weight loss isn’t usually advisable—this is a marathon, not a sprint!

When does orlistat start to work?

You’re unlikely to see dramatic changes immediately. But that doesn’t mean it isn’t doing anything. There are some early indicators you can look out for that suggest the medication is working as it should.

Immediate effects

Orlistat usually starts to affect how you digest fat within the first day or two. How can you tell? Well, look out for some changes when you go to the toilet. Because the undigested fat passes out in your poo, you may notice that your bowel movements are oilier than normal. You may also notice some other gastrointestinal side effects, due to the impact it has on your digestion.

Short-term results

The good news is that, over the first few weeks, these side effects are likely to die down (people in clinical trials have described them as ‘mild and transient’). At the same time, you may start to notice some early results. Weight loss typically begins within two weeks of starting orlistat—although results will vary from person to person.

Long-term results

In one study, patients taking orlistat lost an average of 5.6% of their starting weight within 24 weeks, compared to 2.3% for the control group. Very similar findings have been observed elsewhere, meaning the odds are good that orlistat could work for you over the longer term.

How fast can you lose weight with orlistat?

You should start to see a difference within a few weeks. According to clinical trials, some patients have achieved 5% weight loss by 3 to 6 months and 10% by 12 months. If this doesn’t happen, the NHS suggests it may not be the right medication for you.

Factors affecting weight loss speed

Some people respond much better to orlistat than others, and it’s hard to say exactly why that is. However, it’s clear that your diet makes a huge difference. Because you’ll still be absorbing 70% of the fat you eat, results are best when you switch to a low-fat diet. (That’s the best way to reduce side effects too.)

At the same time, it’s important to consider other lifestyle factors, such as how much you’re exercising, how well you’re sleeping, and whether you’re under a lot of stress. Results may also depend on your starting weight and how consistently you take the medication.

Expected orlistat weight loss timeline

How much weight can you lose on orlistat? Well, this will vary from person to person. In the XENDOS clinical trial, 60% of patients taking orlistat had lost 5% of their body weight within 12 weeks. Of those patients, nearly two-thirds had lost 10% of their body weight by the year mark. For someone weighing 100kg, that’s 10kg.

Side effects and safety considerations

Orlistat can cause side effects, especially when you first start taking the medication or have consumed a high-fat meal. Common side effects include:

• Stomach pain or discomfort
• Urgent need to pass stools
• Oily stools (or oily discharge from your back passage)
• Flatulence
• Headaches
• Other gastric symptoms
• Tiredness

These side effects are typically mild and will go away over time. And although the medication is considered very safe for most people, it can in rare cases be linked with serious side effects like hepatitis, cholelithiasis and rectal bleeding. Some groups of people should not take orlistat, including breastfeeding women, people with cholestasis, and those taking certain medications.

Side effects support at Voy

"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.

Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."

Phoebe Fox - Weight Loss Specialist

Orlistat vs other weight loss treatments

Orlistat is generally more effective than diet and exercise alone. However, it isn’t quite as effective as some of the newer weight loss treatments. On average:

• Wegovy – People taking Wegovy lose almost 15% of their starting weight within 68 weeks. Newer data suggests that a higher dose of 7.2mg could bring this figure to 20.7% over 72 weeks.
• Mounjaro – People taking Mounjaro lose up to 22.5% of their starting weight within 72 weeks.
• Saxenda – People taking Saxenda lose 8% of their starting weight in 56 weeks.

It’s important to remember these are just averages and may not reflect your own results. The best medication for you will depend on your individual circumstances.

How to get best results from orlistat

• Eat a balanced, low-fat diet with no more than 30% of your calories coming from fat.
• Cut down on alcohol. Alcoholic drinks are often surprisingly high in calories (more than 200kcal for a pint of beer and 380kcal for a pina colada). Alcohol can disrupt your metabolism too.
• Stay active. A good target is 30 minutes of moderate exercise, five times a week (this could be as simple as brisk walking). Add in two sessions of strength training (think Pilates, yoga, heavy gardening or lifting weights), to help you maintain muscle mass as you lose fat.
• Make sure to get enough sleep and keep your stress levels under control. Lack of sleep and chronic stress can make it harder to lose weight.
• Talk to your healthcare provider. Let them know if you’re experiencing difficult side effects or aren’t losing weight as fast as you hoped—they should be able to offer you advice or even switch you to a different medication.

Your weight loss journey

Orlistat isn’t for everyone, and it isn’t a silver bullet for weight loss. However, it can be really helpful in the context of some broader lifestyle changes. If you’re curious about orlistat or other weight loss medications, then take Voy’s weight loss quiz to learn more about the best options for you.