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A notepad that says diet on it with various pills and supplements

Do weight loss pills work? 14 of the best diet pills

06 Aug 2021 • 5 min read


Using a natural weight loss supplement could give you the extra boost you need.

Because sometimes, it can be useful to get a helping hand with weight loss. Here's how to know when, how, and why to use fat loss pills.

What are weight loss pills?

Weight loss pills are, as the name suggest, pills that you take to help you lose weight.

As for how they work, they can work in many different ways, and have different effects on different people too.

Some speed up metabolism and increase the rate at which you burn fat, while others curb your appetite or limit how much fat (and calories) your body can absorb from food.1

They’re available as a prescription medication, over the counter drug or dietary supplements and should ideally be taken as part of an overall approach to weight loss, e.g. healthy lifestyle, exercise and diet habits.

They aren’t designed to be a standalone fast and easy weight loss solution. 

Diet pills tend to be prescribed by GPs, in combination with diet and exercise, to people who have a significant amount of weight to lose - typically a Body Mass Index (BMI) of 27 or higher.


Weight loss pills, tablets, supplements are available via prescription, over the counter or as dietary supplement, and are designed to help people work towards their weight loss goals. They aren’t a quick and easy weight loss solution.

Why crash dieting could harm your health

Find out exactly what happens to your body when you embark on a crash diet. 

Do slimming pills work?

Before you think about using a weight loss pill, capsule, tea or supplement, you need to make sure your activity levels and diet are up to scratch.

Pills or supplements are not something to rely on and can never replace a healthy diet, calorie deficit and regular exercise.

  1. Exercise

Are you exercising regularly, with a mixture of cardio and resistance/strength training during the week, which can help you burn calories naturally?

If you’re new to exercise or don’t really have a routine in place at the moment, this article can help – ‘How to create your weekly exercise plan.’

  1. Daily activity

Your daily activity is important, too. Be sure that you walk close to 10,000 steps a day and move your body as much as possible.

Keeping active is key to helping you burn calories and staying trim. It’s also good for your wellbeing too. (For more on this read, ‘How exercise can improve your mental health.’)

  1. Nutrition

Make sure you are consistently eating a healthy diet that supports your weight loss goals and nourishes your body.

The keyword is consistency here and you should ideally be eating food that’s full of a mixture of vitamins, minerals and nutrients.

  1. Calorie deficit

You need to be in a caloric deficit in order to lose weight, so be sure that you have been eating slightly less calories than your body burns.

If you eat more calories than your body uses, your body stores them as fat, which can lead to weight gain. The recommended daily calorie intake is 2,000kcal for men and 2,000kcal for women.

  1. BMI

Your Body Mass Index is based on your weight and height and is generally used to measure health risk.

A BMI of between 25 and 30 is considered overweight, and one that’s over 30 is classed as obese. The higher your BMI, the greater your risk of weight-related illness.

How to calculate your BMI

Body Mass Index (BM) is a useful benchmark for bodyweight and health. But how can you calculate your BMI at home?

  1. Eating habits

Do you snack in between meals? Skip some meals and not others? Eat more sugary and processed food at certain times of the day or night?

Mapping your eating habits and understanding what you do and don’t eat can help when it comes to calorie control.

  1. Medical conditions

For some people, weight gain may be genetical and/or caused by a medical condition, such as Cushing’s disease, diabetes, hyperthyroidism and Polycystic Ovarian Syndrome (PCOS).

Certain medication, including antihistamines for allergies, insulin for diabetes and alpha or beta blockers for high blood pressure, can also lead to weight gain too.

Before putting a weight loss plan in place, speak to your GP to see if there are any underlying medical reasons you may need to factor in.2

  1. Time

Losing weight does take time, especially if you want to be quite a bit slimmer. One pound of fat is the equivalent to around 3,500 calories.3

Weight loss is a journey, it doesn’t happen overnight. But with the right approach and perseverance, it can pay off.

Read more: How to lose weight healthily and keep it off

How do diet pills work?

No product can actually melt fat off your body for you, if only that were possible. But they can make a noticeable difference to your weight and body fat percentage. Diet pills work in several different ways, some of which we’ve listed below:

  • More energy. So you can move your body more during the day, walk more and increase your calorie output.
  • Focus. They can help you focus during your workouts, so you put more effort in (and burn more calories).
  • Burn calories. They will contain natural ingredients that gently raise your body’s ability to burn energy, which can enable you to burn a small, but significant amount of extra calories throughout the day.
  • Curb hunger. They contain ingredients that can help you feel fuller, less hungry and better able to resist treats and snacks because you don’t feel as hungry all of the time.
  • Fat-binding properties. Certain weight loss tablets eliminate fat from meals by binding the fat with dietary fibre from food. This means the binded fat-fibre mass isn’t absorbed by the small intestine and passes out of and isn’t absorbed by the body.4
  • Carb blockers. There are also weight loss tablets that work by preventing the action of the digestive enzyme, alpha-amylase, which allows some of the carbohydrate from food to pass through and out of the gut undigested.5
  • Appetite suppressants. Some weight loss pills, which contain the plant ingredient, hoodia gordonii, reportedly work by actually suppressing your appetite. However, there is limited research to prove this. 6
  • Metabolism boosters. Meanwhile, certain weight loss pills that contain chilli and capsicum, reportedly help you lose weight by speeding up your metabolism, which can lead to you burning more calories and losing pounds in the process.7
  • Breaking down fat. There are also some weight loss pills on the market that inhibit the digestive enzymes that break down fat, which prevents it from being absorbed by the body. These pills are only prescribed to people with a BMI of at least 28 that have failed to reduce their weight through lifestyle changes, such as diet changes and increased physical activity.8

Are weight pills safe?

The best and safest way to use weight loss supplements is to take them every day as directed for a short period of time ( around 2 to 6 weeks).

It’s not advisable to stay on diet pills for a very long time. This is because there’s limited knowledge of the health effects of taking weight loss tablets on a long-term basis.

They may potentially lead to issues that have not yet been identified.9

You should only need the extra support of these products when you are looking for that final boost for your fat loss diet. Alternatively, you might like to take thermogenic or fat burner type supplements when you feel the need for an energy boost for the gym.

Are strong diet pills safe?

There is no straightforward ‘yes’ or ‘no’ answer to this question.

This is because most diet pills tend to have side effects, some more than others, and some worse than others.

What’s more, as with most medication, different diet pills can affect people in different ways.

For instance, some people may experience side effects, such as bloating, diarrhoea, constipation, sleep problems, irritability and memory problems.10

Unfortunately, research on the impact weight loss pills can have on people, if taken for more than 1 to 2 years, is still very limited.

They may cause or lead to problems that have not yet been identified.

That’s why it’s always important to consult your GP before taking weight loss pills and only take the subscribed amount and for the recommended period of time.


Diet pills or supplements are not something to solely rely on for weight loss and should never be used to replace a healthy diet and regular exercise.

The best and safest way to use weight loss supplements is to take them every day as directed for no longer than 6 weeks.

Choosing the right diet pill for you

Be sure to look at the ingredients list so you know you are not intolerant to any of the ingredients.

Fat loss products contain thermogenic aids and caffeine. So if you know that any of these ingredients affect your digestion, mood, or sleep, find a more suitable product.

Take extra care to use the right dose every day, and always take your diet pills with food and water, as directed.

Choose from a store and a brand you trust. And make sure the product is all-natural.

You’ve found the right weight loss supplement when:

  1. It has a clear ingredients list with no confusing ingredients.
  2. You understand everything on the label and are 100% clear on what you are putting into your body.
  3. None of the ingredients give you any side effects like sleeplessness or an upset stomach.
  4. It gives you a gentle boost of energy for your workout.
  5. You notice that you feel less hungry and are able to manage your fat loss diet better.

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We've rounded up 16 of the best weight loss supplements to make it easier for you decide which is best for you.11

  1. Garcinia Cambogia Extract

The skin of this pumpkin-shaped fruit contains hydroxycitric acid (HCA). This is the active ingredient in garcinia cambogia extract, which is marketed as a diet pill.

A study of 130 people compared garcinia against a dummy pill. There was no difference in weight or body fat percentage between groups.

Meanwhile, a 2011 review that looked at 12 studies on garcinia cambogia found that, on average, it caused weight loss of around 2 pounds over several weeks.

  1. Hydroxycut

Hydroxycut contains several ingredients that reportedly help with weight loss, including caffeine and plant extracts. One study in particular found that it caused 21 lbs (9.5 kg) of weight loss over a 3-month period.

  1. Caffeine

Caffeine is renowned for boosting metabolism and can be found in many commercial weight loss supplements.

Some studies have shown that caffeine can boost metabolism by around 3 to 11%, and increase fat burning by up to 29%.

  1. Orlistat (Alli)

This is a pharmaceutical drug that’s sold over-the-counter under the name Alli, and under prescription, as Xenical.

It works by inhibiting the breakdown of fat in the gut, which results in the body absorbing fewer calories from fat.

According to a review of 11 studies, it increased weight loss by 6 pounds (2.7 kg) compared to a dummy pill.

  1. Raspberry ketones

Are naturally found in raspberries; there’s also a synthetic version of them available too.

Research has found that in isolated fat cells from rats, raspberry ketones increase the breakdown of fat and increase the levels of the hormone, adiponectin, which is linked to weight loss.

  1. Green coffee bean extract

These beans are unroasted coffee beans and they contain caffeine and chlorogenic acid, both of which are linked to weight loss.

Caffeine increases fat burning, and chlorogenic acid slows down the rate at which carbohydrates are broken down in the gut.

A number of studies have found that green coffee bean extract can help people lose weight, and a review of research concluded that it made people lose 5.4 more pounds (2.5 kg) than placebo, a dummy pill.

  1. Glucomannan

Glucomannan is a fibre that’s present in the roots of the elephant yam plant. It absorbs water, which makes it gel-like.

When in this state, it sits in your gut and makes you feel fuller for longer, which can help you eat fewer calories.

Three human studies showed that glucomannan, when combined with a healthy diet, helped people lose between 8 and 10 pounds (3.6 to 4.5 kg) in 5 weeks.

  1. Meratrim

Is a combination of two plant extracts that may change the metabolism of fat cells.

It’s believed to help with weight loss by making it more difficult for fat cells to multiply. It also reduces the amount of fat cells pick up from the bloodstream, and helps them burn stored fat.

One 8-week study of Meratrim, which involved 100 people, found the group lost 11 pounds after following a strict 2,000 calorie diet with Meratrim.

It also reduced blood sugar, cholesterol and triglycerides (a type of fat that’s found in our blood).

  1. Green tea extract

Numerous studies have found that main antioxidant in green tea, EGCG, is effective at burning fat. Green tea extract is believed to increase the activity of norepinephrine, a hormone that helps burn fat.

Several studies have shown that green tea extract can increase fat burning and cause fat loss, especially around the stomach.

  1. Conjugated Linoleic Acid (CLA)

CLA is one of the healthier trans fats and is found naturally in some fatty animal foods, such as cheese and butter.

It reportedly reduces appetite, improves metabolism and boosts the breakdown of body fat.

In a review of 18 different studies, CLA contributed to weight loss of around 0.2 pounds (0.1 kg) per week, for up to 6 months.

  1. Forskolin

Part of the mint family, forskolin reportedly increases levels of a compound that’s inside cells called cAMP, which may stimulate fat burning.

A study of 30 overweight and obese men showed that forskolin reduced body fat and increased muscle mass.

  1. Bitter orange

Bitter orange, which is a type of orange, contains the compound, synephrine.

This compound is linked to ephedrine, which used to be a popular ingredient in various weight loss pill formulations.

However, it has since been banned due to serious heart-related side effects. Synephrine works in a similar way to ephedrine – by reducing appetite and increasing fat burning - but is reportedly less potent.

  1. Turmeric

Due to its curcumin content, turmeric can suppress the blood vessels that are needed to form fat tissue.

Plus, it can produce a thermogenic effect in the body, in the same way that ginger does.

Thermogenic means heat-producing and when the body burns calories, it generates more heat, so supplements that boost metabolism or fat burning are considered as being thermogenic.11

  1. Ginger, cinnamon and garlic

Are all believed to have a thermogenic effect on the body too, which increases the body’s internal temperature and results in you using more energy.12

A 15-week study of garlic’s ability to reduce body weight in mice found that garlic did lead to reduced body weight and high-fat diet-induced abnormal plasma and liver lipid profiles.

The mice were fed a high-fat diet (45% fat) for 8 weeks, followed by a high-fat controlled diet supplemented with 2%, or 5% garlic for 7 weeks.13


When shopping around for weight loss pills, make sure you check the ingredients list carefully and take them as advised by the manufacturer.

There are numerous different types of weight loss pills available that contain weight loss-promoting ingredients, such as Garcinia Cambogia extract, caffeine and raspberry ketones.

Handpicked content: What are raspberry ketones?

True or false: Foods that help with weight loss

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Weight loss pills are a whole world in themselves. If you are planning on taking them, make sure you do your research and carefully check the ingredients list to make sure you’re 100% clear on what you are taking, if there are any side effects, and that you aren’t allergic to anything.

While some people may view weight loss supplements as being a magic weight loss wand, this isn’t the case.

Ideally, they should be taken alongside eating a healthy and balanced diet and exercising regularly. They shouldn’t be the only thing you do to help you drop a dress size or more.

What’s more, while they may help you initially lose weight, they shouldn’t be taken long-term, so you’ll need to maintain your weight loss through a combination of healthy eating and staying active.

For more on eating healthily, check out this article, ‘What is a balanced diet?’

The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Last updated: 16 June 2021



Author: Bhupesh PanchalSenior Regulatory Affairs Associate

Joined Holland & Barrett: Apr 2019

Masters Degree in Toxicology and BSc Hons in Medical Biochemistry

Bhupesh started his career as a Clinical Toxicologist for Public Health England, advising healthcare professionals all around the country on how to manage clinical cases of adverse exposure to supplements, pharmaceuticals, cosmetics, industrial chemicals and agricultural products.

After 7 years in this role and a further year working as a drug safety officer in the pharmaceutical industry, Bhupesh joined Holland & Barrett as a Senior Regulatory Affairs Associate in 2019.

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