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 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!
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.
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.
Does orlistat burn existing fat?
Not exactly. While orlistat prevents fat absorption, it doesn’t directly burn stored fat. However, it may help put you at a calorie deficit (in which you’re burning more calories than you consume). When that happens, the body will turn to stored fat as an energy source, leading to weight loss.
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.
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.
- Mounjaro – People taking Mounjaro lose 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.
FAQs
Can I lose weight faster with orlistat?
Yes. Studies have consistently shown that, compared to diet and exercise alone, orlistat leads to faster weight loss.
What happens if I stop taking orlistat?
Some people regain the weight they’ve lost, but that isn’t inevitable. If you’ve made healthy, sustainable lifestyle changes, you’re more likely to keep the weight off even once you stop taking orlistat.
What happens if you take orlistat without eating?
Orlistat works by blocking the absorption of fat in your diet. So if you haven’t eaten, the drug won’t do anything. However, you may still experience side effects, so if you skip a meal, it’s best to skip your dose.
How long can I safely take orlistat for?
If you haven’t lost 5% of your bodyweight by the 3 to 6 month mark, it’s a good idea to speak to your clinician to reassess your plan. Otherwise, you may be able to take orlistat on a long-term basis, at least until your body mass index (BMI) dips below 30. People in clinical trials have taken orlistat for up to four years.
How long does orlistat stay in your system?
Once you stop taking orlistat, the content of your stools usually returns to pre-treatment levels within 48 to 72 hours.
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