Oral weight loss medications: what's available in the UK?

Losing weight is a struggle for many people.

We know that calorie-controlled diets and exercise are proven treatments for obesity. But what if physical activity is difficult and eating habits are hard to shift? It's no wonder we might start searching for something that could give our weight loss journey a head start.

Some may begin by looking at the so-called 'diet pills' on shelves. There are plenty out there. Chemists, health food shops and even supermarkets sell them – and many more are advertised online.

But are they effective? What's in them? And are there any alternatives available?

We'll find out soon enough. But first, we need to make an important distinction.

Are 'diet pills' the same as oral weight loss medications?

Many so-called 'diet pills' are classed as food supplements, not drugs. Others fall under the categories of traditional or herbal medicines.

This is important because MHRA-regulated drugs are subject to strict manufacturing and quality standards. Herbal medicines, traditional medicines and food supplements are not regulated by the MHRA and are not subject to the same standards.

That's not to say these products are inherently bad from a medical perspective. They're not. The problem is that there's limited research looking at their effectiveness – and the studies that exist are often of poor quality.

There are also concerns about how herbal pills and supplements might interact with conventional medications. A 2016 study, for instance, found that folic acid supplements made a bipolar drug called 'lamotrigine' work less effectively.¹

What's in 'diet pills' and how do they work?

It's impossible to explain how each and every 'diet pill' works – if they work at all.

That's because there are many brands on the market, with many making excited and varied claims about their effects – and each containing a hodgepodge of different ingredients.

Research on these ingredients is often limited or poorly designed. A few, like caffeine, are well-known in medicine and have proven stimulant effects. Some stimulants, such as ADHD medications, are known to cause weight loss² but can have dangerous side effects if misused.

Other ingredients have minimal or contradictory data to support their use. Garcinia cambogia extract, for instance, is a common ingredient in 'diet pills' and has been the subject of several short-term studies. The results of these studies varied – some suggested a minor weight loss effect, others found little or none.

If you viewed one of these studies in isolation, you might reasonably believe that Garcinia cambogia was a safe and proven weight loss treatment. But in a 2020 meta-analysis (study of the studies), researchers looked at the available data and concluded that Garcinia cambogia had no clinically significant effect.³

Moreover, herbal treatments containing Garcinia cambogia have been linked to several cases of acute liver failure.⁴

There are two points to make here.

First, just because something is a herbal treatment, it doesn't mean it's 'bad' from a medical perspective. However, herbal treatments and supplements don't enjoy the same rigorous research and safety standards as MHRA-approved medications. That's why it's important to thoroughly examine the available data before you decide to take one of these treatments.

Secondly, just because something is 'natural', it doesn't mean it's automatically good, safe or healthy. Keep your wits about you and take care before putting anything into your body – natural or otherwise.

Are there any approved over-the-counter oral weight loss medications?

There is one MHRA-approved, over-the-counter oral weight loss medication available in the UK. It's a drug called 'orlistat' that's sold under the brand name Alli.

Orlistat has gone through rigorous clinical trials and has been found to be safe and effective when taken according to directions.

You can buy orlistat (under the name Alli) from your pharmacist without a prescription. However, as an over-the-counter medication, it's only available in half-strength (60mg) tablets. If your doctor prescribes orlistat, the dose can go up to 120mg.

Before they sell you the drug, your pharmacist is expected to follow an assessment procedure:



• Your BMI must be 28 or above.
• Your BMI should be checked on each occasion that you request orlistat.
• You must be over the age of 18.
• You should not take orlistat for more than six months when it's supplied over the counter.
• If you have not lost at least 5% of your weight after taking orlistat for three months, you should not continue to take it.

Your pharmacist will also give you advice on the foods you should avoid when taking orlistat.

How does orlistat work?

Orlistat belongs to a group of drugs called lipase inhibitors. Lipase is an enzyme in your gut that allows you to absorb fat from food. Orlistat makes you produce less lipase.

The 60mg tablet will prevent about a quarter of the fat from your food from getting absorbed. This undigested fat is passed in your stool (poo) when you go to the toilet.

How effective is orlistat?

The prescription strength Orlistat 120mg is more effective than the 60mg over-the-counter dose. It will prevent about a third of the fat from your food from getting absorbed.

Whichever strength you take, it's only a percentage of your fat intake that's affected. You will still need a low-fat diet to lose weight. With the 120mg tablet, it's possible to achieve weight loss of 2.9% in 12 months.⁵

What are the side effects of orlistat?

Most of the side effects are related to the amount of undigested fat your body has to pass in your stool. So, the less fat you take in the better – but you still may experience:

• Fatty or oily stool
• Oily discharge (you may see greasy spots on your underwear)
• Passing wind
• Needing the toilet urgently
• Passing stools more often
• Severe diarrhoea when taken with the contraceptive pill

Are there any other weight loss tablets on prescription?

Three more oral weight loss medications are available on prescription. They're all appetite suppressants – they work by making you feel less hungry between meals.

Here are the details.