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What are diet pills and how do they work?

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We all know that the best way to lose weight is to consume fewer calories and do regular exercise. But lots of people find this difficult and get frustrated when they don’t see quick results.

Weight loss doesn’t tend to be a quick process, but there are plenty of resources out there to help you, including the free 12-week weight loss plan available from the NHS. There are also medicated treatments you can try, including our weight loss service, and diet pills like orlistat.

If you’re trying to lose weight and you’re thinking of trying diet pills, it’s a good idea to speak to your GP first. Many diet pills are considered unsafe or ineffective by the NHS, so it’s important to get the right one and to take it in the correct way.

What are weight loss pills?

Weight loss pills are tablets taken as part of a healthy diet and exercise regime to encourage weight loss. There are many kinds available, but most aren’t considered effective by the NHS.

Some types of diet pill may be ineffective in reducing weight. Others may be effective but considered too risky to use by UK or European medical agencies. For this reason, some diet pills that might be available elsewhere in the world won’t be available in the UK.

Weight loss pills containing phentermine and topiramate have been shown to help reduce weight, but they aren’t authorised for use by the European Medicines Agency due to safety concerns. There are other pills that have been banned in the UK.

Do weight loss pills actually work?

Pills containing the active ingredient orlistat, such as alli, are considered an effective weight loss aid by the NHS. Other types may have had successful clinical trials, but aren’t yet recognised by the NHS simply because more research needs to be done.

It’s important to remember that diet pills need to be taken as part of a healthy and balanced diet. When taken on their own, without any lifestyle changes, it’s unlikely that a weight loss pill will have any effect.

What is the most effective weight loss pill?


Orlistat is considered an effective weight loss treatment by the NHS. It works by preventing your body from digesting some of the fat you eat. Undigested fat is then passed out of your body in your poo.

Orlistat is a prescription diet pill but it can be bought over the counter under the brand name alli and Orlos. Under prescription, orlistat sometimes has the brand name Xenical. Our Online Doctor service can prescribe this weight loss pill, you’ll need to answer a few questions to make sure it’s right for you.

Multiple studies have demonstrated the benefits of orlistat when taken with a calorie-controlled, low-fat diet.

One showed the following:

  • After 12 weeks of taking orlistat, 60% of people lost at least 5% of their baseline bodyweight
  • At one year of taking orlistat, 62% of these people had gone on to lose at least 10% of their baseline bodyweight

Taking orlistat can be a good way to stop you from gaining weight, but it should be taken as part of a healthy balanced diet and exercise plan.

Fat-binding pills

Fat-binding pills contain an active ingredient said to bind dietary fat to fibre. This helps the fat pass through the body without being digested.

The weight loss pill XLS-Medical Fat Binder contains Litramine, which is derived from a cactus plant. In some studies (including this one from 2014) Litramine has been found to safely promote weight loss.

Although this type of medication isn’t officially recognised by the NHS, you may find that it works for you as part of a healthy diet and exercise regime.


Clavitanol is found in XLS-Medical Max Strength weight loss pills. This ingredient, which is derived from plants, is said to reduce the amount of carbohydrates, fats, and sugars absorbed from our food.

In one clinical study, Clavitanol was found to promote weight loss without causing adverse effects. In another study, it was found to lower blood glucose levels after eating.

As with fat binders, this medication isn’t recognised by the NHS, but you may still find that it works for you when taken as part of a healthy diet. When ordering these pills online make sure to look for trusted retailers who are registered with the GPhC.

Also bear in mind that you’ll need to complete a short questionnaire. This allows pharmacy teams to make sure the pills are safe for you to take.

Carb blocker pills

Carb-blockers are weight loss pills that limit the digestion of carbohydrates. Some types of type 2 diabetes medication are carb blockers, and are available on prescription if your doctor thinks they’ll help with your condition.


Some weight loss pills such as Adios Max are derived from a type of seaweed known as bladder wrack (Fucus vesiculosus). This natural substance is said to have been used in traditional medicine to help with weight loss, as well as conditions like joint pain and arthritis.

However, there is very limited evidence to suggest that bladder wrack can help with weight loss. When taking any medication make sure it’s the best option for you and speak to a healthcare professional.

How to use diet and exercise for weight loss

Whether or not you’re using diet pills, your weight loss journey will need to incorporate a healthy diet and regular exercise.

The NHS recommends that the average person looking to lose weight should eat 600 fewer calories each day, and should favour fruits, vegetables, high-fibre carbohydrates, and lean protein.

Some simple tips for making your diet easier include the following:

  • Fill out your plate with more fruit and veg
  • Drink more water – sometimes thirst can feel like hunger
  • Eat foods high in fibre to fill you up
  • Use a smaller plate to control your portion sizes
  • Plan your meals

For more weight loss inspiration, read our tips on how to lose weight healthily.

Weight loss service



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