Weight Loss Medications: Are They Effective?
There’s a reason healthcare professionals sometimes prescribe weight loss medications. As part of a lifestyle programme, weight loss drugs can help people lose three to 12 percent more of their starting body weight versus healthy eating and exercise alone.
But with so many headlines and celeb soundbites about weight loss injections and pills, which treatments genuinely deliver — and which are overhyped?
Below, we’ll look at the best weight loss medication options available in the UK, from weekly injections like Wegovy® to weight loss pills that actually work, such as orlistat and Mysimba®. We’ll cover how each medication for weight loss works, typical results, and safety facts.
The Main Types of Weight Loss Medications in the UK
The Medicines and Healthcare products Regulatory Agency (MHRA) has approved several weight loss medications.
These drugs can be split into five main categories:
GLP-1 receptor agonists
GIP/GLP-1 agonists
Lipase inhibitors
Appetite and cravings modulators
Biguanide
Here’s what you need to know about each of these medications.
1. GLP‑1 Receptor Agonists (GLP‑1s)
These injectable drugs mimic glucagon‑like peptide‑1, a gut hormone that tells your brain you’re full, steadies blood sugar levels, and slows stomach emptying. As a result, you may find it easier to stick to a healthy diet.
There are two main types of GLP-1 weight loss injections in the UK, Wegovy® (semaglutide) and Saxenda® (liraglutide):
Wegovy® is a weekly injection. In a 68-week clinical trial, people who took Wegovy® lost an average of 14.9 percent of their starting weight.
Saxenda® is a daily injection. Research suggests people lose an average of 4.81 percent of their weight when using 3.0mg (milligrams) liraglutide for at least one year.
Semaglutide is also the active ingredient in brand-name medications Ozempic® and Rybelsus®, but these medications are only licensed for treating diabetes. Off-label use is currently discouraged by the NHS (National Health Service) due to supply issues affecting diabetes patients.
Likewise, the diabetes medication Victoza® also contains liraglutide.
2. Dual GIP/GLP‑1 Agonist
Another popular weight loss injection is tirzepatide.
This medication is a dual GIP and GLP-1 agonist. Like GLP-1, glucose‑dependent insulinotropic polypeptide (GIP) is another satiety hormone that also affects insulin release.
In a randomised placebo-controlled clinical trial called SURMOUNT‑1, 2,539 adults were given tirzepatide or a placebo injection for 72 weeks. The participants given tirzepatide lost an average of 15 percent of their starting weight.
In a later phase of the trial called SURMOUNT-4, 670 participants received 10mg or 15mg of tirzepatide on a weekly basis for 36 weeks. The group lost an average of 20.9 percent of their starting body weight.
In November 2023, the MHRA licensed Mounjaro®, a tirzepatide-based weight loss injection.
Zepbound® is another branded version of tirzepatide. It’s currently available in the United States but not in the UK.
3. Lipase Inhibitor
Now, we’re getting into weight loss pills. Firstly, let’s look at orlistat — known by the brand names Xenical® and Alli®.
Orlistat is a lipase inhibitor, which is a fancy way of saying it blocks fat absorption from food. Research shows that orlistat can be an effective weight loss treatment when combined with a reduced-calorie diet and regular exercise.
In the XENDOS study, participants who were treated with orlistat lost an average of 5.8kg (kilos) over a period of four years.
In addition to helping you lose weight, orlistat could also help you maintain weight loss.
4. Appetite and Craving Modulator
Mysimba® is a prescription-only weight loss pill that contains two active ingredients — naltrexone and bupropion.
Bupropion is often used to help people quit smoking and for treating depression, while naltrexone is used to treat alcohol and drug dependence. Together, these medications work on the brain’s hunger centre and reward system to reduce appetite and help control cravings.
According to the COR‑II randomised clinical trial, people with obesity who were treated with Mysimba® lost around 6.4 percent of their starting weight. However, as with most other studies on weight loss drugs, the participants also engaged in healthy lifestyle changes like sticking to a reduced-calorie diet and engaging in regular physical activity.
Mysimba® requires careful monitoring and is contraindicated in patients with uncontrolled hypertension, seizure disorders, or those taking monoamine oxidase inhibitors (MAOIs).
In the United States, naltrexone-bupropion is also sold under the name Contrave®.
5. Metformin (Biguanide)
Metformin is another prescription oral medication which can be used for weight loss.
Like semaglutide and liraglutide, metformin was primarily used to treat type 2 diabetes. It’s occasionally used off-label to treat polycystic ovary syndrome (PCOS) and help with modest weight loss.
While it isn’t an MHRA-authorised weight loss drug, metformin can help produce modest weight loss — partly because it seems to reduce appetite.
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Do Weight Loss Medications Really Work?
In short, yes. Plenty of evidence shows these weight loss medications can work. Not only can these drugs assist with weight management, but they may also decrease the risk of weight-related health conditions like high blood pressure (hypertension), heart disease, and sleep apnoea.
Remember, though, not everybody will experience the same results on the same medicines.
Your success will depend on:
The exact medication you take
Your unique physiology
How well you adhere to your medicine protocol (in other words, if you take your meds on time and correctly)
Your caloric intake (how many calories you eat and drink each day) and physical activity levels
Weight loss medicines work best alongside a calorie-controlled, healthy diet and at least 150 minutes of weekly exercise. See the UK Chief Medical Officers’ physical activity guidelines and the NHS’s Eatwell Guide for general guidance.
How Quickly Can You Expect Results From Weight Loss Medications?
According to the studies mentioned above, most people see some weight change within the first four to 12 weeks of using a weight loss medicine.
NICE recommends reviewing weight loss medication effectiveness at three months for orlistat and six months for GLP-1 agonists. If you haven’t lost at least 5% of your starting weight, your prescriber may recommend stopping or changing treatment.
If you’re concerned you’re not losing weight quickly enough, it may be a good idea to reassess your diet and physical activity levels.
If you’re eating in a calorie deficit and exercising regularly but still aren’t losing weight, think about making a follow-up appointment with your healthcare provider.
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Common Side Effects and Safety of Weight Loss Medications
As with all medications, drugs for weight management can come with certain risks and side effects.
Some of these side effects are common and mild. Other, more serious side effects can happen, but they’re generally rare.
Here’s a table on the side effects of each class of weight loss drugs.
Drug class | Common side effects | Rare but serious side effects |
GLP‑1 and GIP‑GLP‑1 | Nausea, diarrhoea, constipation | Pancreatitis, gallstones, possible thyroid C-cell tumours (seen only in rodent studies) |
Mysimba | Headache, insomnia, dry mouth | Increased blood pressure, mood changes, seizures |
Orlistat | Oily stools, urgent bowel movements | Severe liver injury |
Metformin | Bloating, loose stools | Lactic acidosis (very rare) |
Often, the mild side effects can be treated with non-prescription medicines. Listen to your body. Stay hydrated and rest if you’re not feeling well.
In the UK, the MHRA Yellow Card scheme monitors side effects. Be sure to report your side effects to your prescriber and directly to the Yellow Card scheme online or through the app if you’re experiencing severe or persistent side effects.
How to Access Weight Loss Medication UK
All weight loss medications are prescription‑only medicines in the UK.
Broadly, you have two routes:
NHS referral via your GP (general practitioner)
Private care through a regulated clinic or a telemedicine provider
Note that private medical insurance (PMI) typically doesn’t cover weight loss medications, as they're considered lifestyle treatments.
Let’s look at each of these options in a bit more detail.
NHS Pathway to Weight Loss Medication
The NHS offers access to weight loss medications, but only if you meet the National Institute for Health and Care Excellence (NICE) criteria for accessing the specific medicine.
Usually, this means your body mass index (BMI) must be higher than a specific number, or you have a weight-related medical condition.
If you go through the NHS, you may also have to join a long waiting list.
Private Pathway to Weight Loss Medication
Private clinics can prescribe weight loss medications within MHRA parameters. Typically, the criteria is a BMI of at least 30 kg/m² or at least 27 kg/m² if you have a weight-related health condition. You pay out‑of‑pocket with a private clinic, but access is faster and more convenient.
Hers UK offers the following weight loss medications:
Mounjaro®
Wegovy®
Orlistat
We also offer fast delivery, lifestyle support, and unlimited follow-ups with your care team.
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The Bottom Line on Medication for Weight Loss
Losing weight can be a rewarding, albeit tough, journey. Weight loss medications aren’t a magical solution, but they can make it easier to drop excess kilos — especially when combined with healthy lifestyle changes.
Keep the following in mind:
There are several weight loss medications available in the UK. These include injectable medicines like semaglutide, liraglutide, and tirzepatide, along with pills like orlistat and Mysimba.®
They’re effective. When used alongside regular exercise and a healthy diet, these medications can be highly effective at helping you achieve a healthy weight.
There’s no single best weight loss medication for everybody. The right choice depends on your BMI, health, budget, and side effect tolerance.
Hers UK offers numerous weight-loss medications, including Mounjaro®, Wegovy®, and orlistat.
We’ll help you connect with a licensed medical provider who can help you formulate a treatment plan and — if appropriate — prescribe weight loss medication.
Ready to explore medically backed options? Start by taking the free Hers UK assessment to see if prescription weight loss support fits your goals.
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your GP about the risks and benefits of any treatment.