On the face of it diet pills seem like an easy answer to losing weight, but not all of them are proven effective or safe to use. Only one is approved for use by the NHS and many of the weight loss supplements available to buy online are unregulated. In this blog, we look at what diet pills are currently on the market and how they work.

Prescription weight loss medications

Orlistat – also sold under the brand name Xenical – is the only weight loss drug used by the NHS. Doctors and pharmacists use these pills to treat obesity in patients who have:

  • A BMI over 30 or
  • A BMI over 28 and high blood pressure, high cholesterol, or type 2 diabetes

The active ingredient – orlistat – works by binding itself to the enzymes (lipases) that break down fat. If the body can’t break down fat, it can’t absorb it, and so it simply passes through the gastrointestinal system and leaves as waste.

Orlistat can prevent up to 30% of the fat you eat from being absorbed, but to work effectively, it must be taken as part of a low-fat diet. This means eating less fat in every meal, so if your meal is 1000 calories, only 300 of those should come from fat.

Studies show that Orlistat is effective in reducing weight as part of a weight management plan that includes diet and exercise. One study¹ showed that:

  • 60% of participants lost 5% of their body weight after 12 weeks of taking Orlistat
  • 62% of those people went on to achieve a 10% loss after 12 months

Doctors recommend that you stop taking Orlistat if you haven’t lost at least 5% of your body weight after 12 weeks. If you haven’t reached your short-term weight loss target by then, Orlistat is unlikely to work for you long-term.

A lower-strength version of Orlistat is available to buy over the counter. Alli and Orlos contain 60mg of orlistat, half that of the prescription drug, Xenical (120mg).

Over-the-counter weight loss pills

There are lots of weight loss pills available to buy off the shelf in supermarkets and online. Each works in a slightly different way – some are made to boost metabolism, while others reduce appetite, or block the absorption of fat and carbohydrates.

Fat-binding pills (e.g., XLS-Medical Fat Binder) 

Fat-binding pills contain a dried extract from the cactus plant, that binds fat to the fibre you eat so it passes through the body without being absorbed. Its manufacturers claim that it has fewer side effects than Orlistat but as this isn’t an approved NHS drug.

Carb-blocker pills (e.g., XLS-Medical Carb Blocker) 

As the name suggests, carb-blocker pills work by limiting how much carbohydrate your body absorbs. Some type 2 diabetes drugs are also carb-blockers, such as Glucobay (acarbose) and Glyset (miglitol) and they may be available to you on prescription, if your doctor thinks you would benefit from using them.

Clavitanol pills (e.g., XLS Medical Max Strength)

This pill uses a plant extract to reduce the amount of carbohydrate, fat, and sugar your body absorbs. Though some studies have proven that the active ingredient, clavitanol, can limit weight gain, it is not recognised by the NHS.

Some of the dietary supplements available on the market contain natural ingredients like seaweed or chilli. These extracts have traditionally been used to increase weight loss, but there is no clinical proof to back up many of the claims made.

woman taking a pill

Weight loss and diabetes

Some diabetes medication can facilitate weight loss, such as:

  • Incretin drugs
  • SGLT-2 inhibitors
  • Alpha-glucosidase inhibitors

If you have type 2 diabetes and you’re overweight, talk to your doctor. You may benefit from using one of these treatments to help you reach your weight loss goal.

Are weight loss pills safe?

Weight loss pills are not suitable for everyone, so we recommend speaking to your doctor or pharmacist before you take them. If you’ve been trying to lose weight for a while but you’re not getting the results you’d like, diet pills may not hold the answer.

Buying pills online from unregulated sellers could leave you out-of-pocket at best, and at worst you could end up suffering serious side effects.

In a survey by the UK medicines regulator (MHRA), 63% of the people who said they’d bought diet pills online had gone on to suffer unpleasant side effects, including diarrhoea, blurred vision, bleeding, and heart problems².

Regulated health care sites will check to make sure that it is safe for you to take weight loss pills before they sell them to you. Their trained staff will ask about your medical history, your mental health, and any other medication you are taking.

Buying diet pills online safely

Not all diet pills sold online are licensed for use in the UK – some are counterfeit and don’t contain the ingredients they claim to, while others have not been proven safe.

Weight loss pills containing phentermine and topiramate, for example, are not considered safe by the European Medicines Agency, and the slimming pill sibutramine (Reductil) was suspended by the UK regulator in February 2010.

The best way to ensure that the diet pills you are buying are genuine and safe to use, is to use a regulated pharmacy. All pharmacies – both online and off – should be registered with the General Pharmaceutical Council (GPhC). Look for the accreditation logo on the pharmacy’s website or their registration number.

You could also check to make sure that the online pharmacy you are using is connected to a physical premises. Online pharmacies should be linked to a “bricks and mortar” premises. At Post My Meds, for example, we also have a pharmacy in Twickenham.

The key takeaway

If you’re not losing the amount of weight you’d like, then diet pills might be able to help. To ensure they’re safe to take, stick to prescription medications, like Orlistat, and only buy over-the-counter alternatives if it’s from a regulated pharmacy.

Your doctor or pharmacist can check that you are suitable to take the treatment, and ensure there are no harmful drug interactions that might interfere with any other medication you are taking. They might also suggest an alternative if they think you’d benefit from using a different type of weight loss technique.

Weight loss pills and dietary supplements are most effective when they’re used as part of a calorie-controlled diet that includes exercise to burn more calories. By creating a plan for yourself with a weight loss target, you’ll find it easier to reach your goal.

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 Oct 21, 2021 by Joseph Issac, MPharm
Reviewed Oct 19, 2021 by Prabjeet Saundh, MPharm