Losing weight can feel like climbing a mountain – when you’re at the bottom and you’re looking up at the summit, it’s impossible to imagine yourself ever reaching the top. So, if someone comes along with a tempting shortcut – diet pills, for example – then you’re going to take it. In reality, weight loss medication is only effective when it’s combined with diet and exercise, but it can help people with a high BMI to shed some weight.

Prescription diet pills vs. over-the-counter

Some weight loss capsules are only available on prescription from a doctor. Orlistat (also sold under the brand name Xenical) is the only NHS-approved weight loss drug. 

It’s used by doctors to treat obesity in patients who have a body mass index (BMI) of: 

  • Over 30 or, 
  • Over 28 and either high blood pressure, high cholesterol, or type 2 diabetes 

Orlistat is also available to buy over the counter under the brand name, Alli. It has the same active ingredients but is half the strength of the prescription medication. 

Search for ‘weight loss pills‘ and Google will return hundreds of products, all claiming to be the most effective, but most of them are unregulated, so how can you be sure? 

Medicines like Orlistat are tested for their safety and efficacy by the UK regulator before they are made available to the public. With much of this data available to read online, you can make up your own mind before you hand over your hard-earned money. 

Do weight loss capsules actually work? 

Patients taking prescription weight loss medication can expect to lose around 5 – 10% of their body weight – more than they would using diet and exercise alone. 

Over six months researches gave 80 people with a BMI of over 30 either 120mg of orlistat or a placebo drug three times a day. They found that the group taking orlistat lost more weight than the placebo group (4.65kg vs 2.5kg – orlistat vs placebo)¹

In addition to losing a clinically significant amount of weight, those taking orlistat also saw a reduction in their waist circumference, BMI, and cholesterol levels. 

Another study looking at the effects of Alli (over-the-counter orlistat), found that when it was combined with diet and exercise over 12 months, more than 40% of the participants lost 5% of their body weight –5.7lbs more than the control group² 

Though these studies show how effective diet pills can be, they only work when they are used as part of a more inclusive weight loss management plan. 

How to use Orlistat for maximum benefit 

Doctors prescribing Orlistat monitor their patients’ progress carefully. It doesn’t work for everyone, so if after 12 weeks you haven’t lost at least 5% of your body weight, then it’s unlikely that this medication is going to work for you. In this case, your GP or pharmacist will discontinue the treatment and discuss other options with you. 

Orlistat pills work by inhibiting the enzymes in your body that break down fat. If it can’t be broken down, then it can’t be absorbed, and so it simply leaves your body as waste. 

There are things you can do to maximise its effectiveness: 

  • Orlistat should be taken as part of a calorie-controlled diet – for it to work, your daily fat intake should not exceed 30% of your total calories. 
  • Aim to exercise four or five days a week (either 150 minutes at a moderate pace or 75 minutes at a vigorous pace spread over the course of a week).
  • Orlistat works best when it’s taken as part of a well-balanced diet that is rich in fruit and vegetables, and low in sugar and fat.

Some people also find that taking time to de-stress positively impacts their weight loss journey and can even contribute to maintaining a healthier lifestyle long-term 

The controversy over diet pills 

Orlistat is approved for use by the Medicines and Healthcare Regulatory Agency (MHRA) in the UK (the US equivalent is the Food and Drug Administration). It’s the only prescription medicine available on the NHS but you can also buy it online. 

Some ‘diet pills’ are marketed as dietary supplements and because they are not classed as medicines, they don’t come under the jurisdiction of the MHRA. Any claims they make about being able to help you lose weight fast should not be taken at face value. 

When you’re buying weight loss supplements, it’s important that you do your homework. 

We recommend that you only buy medicines from pharmacies that are registered with the General Pharmaceutical Council (GPhC). Registered pharmacies, like Post My Meds, only stock regulated products so you can be sure you’re getting the real deal. 

Every year, the MHRA seizes thousands of pills that are counterfeit or banned in the UK. 

These pills are unlikely to help you lose weight, and some have even been known to contribute to weight gain. Worse still, they pose a significant health risk.  

The key takeaway 

Studies have shown that Orlistat 120mg and its lower-strength, over-the-counter alternative, Alli, can help people lose weight. However, they are only effective when they are used alongside diet and exercise as part of a wider treatment plan. 

There is no easy way to lose weight, it’s a long-process that requires dedication, and though it might seem tempting, you should be cautious about believing the claims made by some of the supplements marketed as ‘weight loss capsules’.

Although all of our content is written and reviewed by healthcare professionals, it should not be substituted for or used as medical advice. If you have any questions about your health, please speak to your doctor.

Authored Dec 10, 2021 by Joseph Issac, MPharm
Reviewed Feb 16, 2022 by Prabjeet Saundh, MPharm