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Weight loss pills: How do they work and are they effective?

Weight loss pills are used to help people with obesity or overweight to lose and manage weight.

Weight Loss Pills: How Do They Work and Are They Effective? | Juniper

You've probably heard all the rage about weight loss drugs — from weight loss injections to weight loss pills. You might even be wondering what's the deal with all these weight loss drugs, especially with so much information hitting the headlines and your social media feeds.

Weight loss pills are used to help people with obesity or those who are overweight to lose weight and manage their long-term weight in combination with lifestyle changes like following a balanced diet and increasing how much exercise you fit into your week.

If you've been on a journey trying to lose weight and are considering all your options, we're diving deep into everything you need to know about weight loss drugs, how they work and how effective they are and what alternative prescription weight loss drugs are on the market.

What are weight loss pills?

Weight loss pills are a type of weight loss medication administered orally to treat obesity in combination with lifestyle changes like following a reduced-calorie diet and increasing physical activity.

Much like other weight loss treatments, weight loss pills are prescription drugs that need to be discussed with your healthcare provider to see if they're right for you.

There are a few different types of weight loss pills on the market. But only one weight loss pill is approved in the UK to help people with obesity or those with a high body mass index (BMI) lose weight.

Orlistat (also known as Xenical and Alli) is a type of weight loss pill that is available as a prescription from your doctor or is available in a lower dose form from a pharmacy.

Orlistat (Xenical) is the 120mg version of Orlistat and is only available with a prescription if you have a BMI of 28 or more and also have a weight-related health condition or a BMI of 30 or more.

Without a prescription, you can buy Orlistat, which is a low-dose version of Orlistat called Alli. To purchase Alli, you must be over 18, express that you are willing to make lifestyle changes like following a calorie-reduced healthy diet and have a BMI of 28 or over.

Orlistat works by preventing roughly 1/3 of the fat from food intake from being absorbed. Instead, the undigested fat is passed out with your bowel movements instead of being absorbed by your body [1].

Lipase, an enzyme contained in the digestive tract, works to break down dietary fat into smaller parts that are used or stored for energy. Orlistat blocks the lipase so the fat isn't broken down and is moved through bowel movements [2].

Do weight loss pills work?

Like all weight loss drugs, weight loss pills aren't a magic, quick-fix solution to weight loss. It's important to remember that weight loss and weight management require lifestyle changes that you can keep up with over the long term.

But, weight loss pills can be helpful for some people. Research shows that those taking Orlistat who also reduced their calorie intake and increased physical activity lost weight by 10% more on average in one year than those who weren't taking Orlistat [3].

Other studies have shown that among people with obesity, those taking Orlistat saw a 5.63% weight reduction in comparison to 2.3% in the placebo group [4].

However, according to the NHS, Orlistat as a weight loss treatment should only continue past 3 months if 5% of your body weight has been lost, as Orlistat can affect how you digest fat within 1-2 days. After the 3-month mark, if you haven't seen weight loss improvements, the medication is likely to be ineffective for you [1].

What are the side effects of weight loss pills?

Weight loss medication can come with some side effects, so it's important to consider both the common side effects and severe side effects that are associated with these medicines.

The most common side effects of Orlistat happen as a result of the fat passed out of your body with bowel movements. This might result in fatty and smelly stools, feeling an increased urge to go to the toilet and oily spotting on your underwear. These side effects can be curbed by following a low-fat diet and tend to go away over time [5].

In rare cases, there are more serious side effects including [5]:

  • Changes in hearing
  • Diarrhoea
  • Dark, bloody, or cloudy urine
  • Painful urination
  • Fast heartbeat
  • Ear aches

What are other types of weight loss medications available?

Aside from weight loss pills, there are other weight loss medications you can consider, including weight loss injections that are designed to help with weight loss and weight management.

In the UK, other prescription weight loss drugs that are approved include Wegovy (which contains the active ingredient semaglutide) and Saxenda (which contains the active ingredient, liraglutide).

Both these prescription weight loss drugs work similarly and belong to the same family of medications that mimic the GLP-1 hormone that's naturally controlled by the gut and controls blood sugar and insulin. This keeps you fuller for longer and helps you reduce food intake, which can support weight loss [6].

The main difference between Wegovy and Saxenda is the active ingredient in each weight loss drug. Saxenda contains the active ingredient liraglutide and Wegovy contains the active ingredient semaglutide.

Both Wegovy and Saxenda can help people with obesity who have a BMI over 30 or those who are overweight with a BMI over 27 who also have at least one weight-related medical problem [7]. Both of these weight loss drugs have demonstrated effective results in helping people lose weight when making lifestyle changes including following a balanced diet and engaging in regular exercise.

What weight loss medications are most effective?

Prescription weight loss drugs can be really effective and helpful in assisting people in losing weight. Let's take a closer look at these treatment options and how effective they are in aiding weight loss.


As we've already mentioned, research has shown that those using Orlistat as a treatment option who also followed a decreased calorie diet and increased their exercise lost weight on average by 10% more than those not taking weight loss medicine.

Saxenda (liraglutide)

Clinical trials found that those taking Saxenda lost 5-10% of their body weight when combined with diet changes and increased exercise in comparison to the placebo group [8].

Wegovy (both semaglutide)

Wegovy contains the active ingredient, semaglutide, which has been shown to reduce body weight by an average of 15% [9]. Now that is impressive! In fact, semaglutide has been found to be the most successful medication for weight loss results [10].

In our Weight Reset Programme, we combine Wegovy with health coaching and community support to help you lose weight and improve your health. Our programme focuses on these 3 key areas in order to support you in losing weight sustainably and with the knowledge that you'll be able to keep it off in the long term.

Comparing the weight loss drugs

When comparing the weight loss drugs, Orlistat shows the weakest weight loss results with only 10.2% of patients losing 10% of their body weight, while 66.1% of patients taking Wegovy lost 10% of their body weight [11][12].

When comparing Wegovy to Saxenda, the group taking Wegovy lost 16% of their initial body weight, in comparison to 6% amongst those taking Saxenda [13].

A 2021 study about the effect of a comparable medication available at Juniper, at 68 weeks, 69.1% of participants had lost more than 10% of body weight, and 50.5% had lost more than 15%. The average weight loss after 68 weeks is 14.9%, and one in three participants lost at least 20% of body weight [14]. 

If you are considering weight loss drugs in order to lose weight, a specialist weight management program like Juniper can support you on your journey to losing weight.

Through medication, our weight loss treatment gives your body a biological reset that targets areas of the brain that regulates appetite and lowers your body's set point, which helps you achieve your weight loss goals.

Our clinical team are also by your side throughout your weight loss journey, here to offer you tailored support and practical tools you need to lose weight. Our health coaches guide you with helpful and actionable advice and support you to rebuild the habits that will help you keep the weight off in the long term.

Plus, we connect you with other women who are on the weight loss journey with you, which has been shown by several studies to motivate greater weight loss than those doing it alone [15].

Ultimately, navigating weight loss and weight management can be difficult for many people. Luckily, there are prescription medications available on the market to make the journey a little less challenging. It's important to seek medical consultation to figure out which weight loss drugs are right for you and your situation to get the most effective results.