Weight Loss Medications
A detailed guide to the medications we prescribe for weight loss: what they cost, how they work, how to take them, the side effects, and how our service works.
This guide covers the medications we use most commonly for weight loss at BGM Medical. Prices are rough UK guide prices only, they fluctuate and vary between pharmacies, and are not a quote. It is intended to sit alongside, not replace, a conversation with your doctor. For general advice on weight, health risks, and lifestyle options, see our general weight loss guide.
An overview
There are two main groups of medication licensed for weight loss in the UK: GLP-1 (and dual GIP/GLP-1) receptor agonists, given by weekly injection, and oral tablets that work in different ways. None of these medications work in isolation, they work best alongside the lifestyle changes covered in our general guide.
Semaglutide, Tirzepatide & Liraglutide
Weekly (or daily, for Liraglutide) injections that reduce appetite and slow digestion. Currently the most effective options in terms of average weight loss.
Orlistat & Naltrexone-Bupropion
Tablet-based options for people who prefer not to inject, or where injectable medications are not suitable. Generally produce more modest weight loss.
An assessment does not guarantee a prescription
Undertaking an initial assessment with us does not guarantee that we will issue a prescription. We will only advise on, or issue, a prescription where we consider the medication clinically suitable and safe for you specifically. If a medication is not appropriate, we will explain why and discuss other options.
Semaglutide
GLP-1 receptor agonistWegovy (weight loss) / Ozempic (diabetes brand, sometimes used off-label)
A once-weekly injection and one of our most commonly prescribed weight loss medications. Well studied, with the longest track record of this drug class.
Rough UK price: Roughly £150–£220 per month, depending on dose and pharmacy.
How it works
A GLP-1 receptor agonist. It mimics a natural gut hormone (GLP-1) that is released after eating. It reduces appetite, increases feelings of fullness, and slows the rate at which the stomach empties.
How to take it
- Injected subcutaneously (under the skin) once a week, on the same day each week.
- Usually given into the abdomen, thigh, or upper arm using a pre-filled pen.
- Rotate the injection site each week to reduce irritation.
- Dose is increased gradually (titrated) over several months to the target dose to reduce side effects.
- Store in the fridge; most pens can be kept at room temperature for a limited period, check the leaflet.
Pros
- +Average weight loss of around 15% of body weight in clinical trials (STEP 1 trial, 68 weeks)
- +Longest safety track record of the GLP-1 medications
- +Once-weekly dosing
- +Also licensed for type 2 diabetes, useful if this is a relevant consideration
Cons
- −Gastrointestinal side effects, especially early on and after dose increases
- −Requires an ongoing injection; not an oral option
- −Weight regain is common if stopped without a maintenance plan
- −Not suitable during pregnancy or breastfeeding
Common side effects
Tirzepatide
Dual GIP/GLP-1 receptor agonistMounjaro
Our most potent option for weight loss, acting on two gut hormone receptors rather than one. Often the first choice where maximum weight loss is the priority and it is otherwise suitable.
Rough UK price: Roughly £150–£250 per month, depending on dose and pharmacy.
How it works
Acts on both GLP-1 and GIP receptors, two separate gut hormone pathways. This dual action tends to produce a stronger effect on appetite and blood sugar than GLP-1 agonists alone.
How to take it
- Injected subcutaneously once a week, on the same day each week.
- Usually given into the abdomen, thigh, or upper arm using a pre-filled pen.
- Rotate the injection site each week.
- Dose is increased gradually over several months.
- Store in the fridge; check the specific pen leaflet for room-temperature limits.
Pros
- +Average weight loss of around 15 to 21% of body weight in clinical trials (SURMOUNT-1, 72 weeks), the highest of any licensed option
- +Once-weekly dosing
- +Strong effect on blood sugar control as well as weight
Cons
- −Generally the most expensive of the weight loss injections
- −Gastrointestinal side effects, similar profile to semaglutide but sometimes more pronounced during titration
- −Requires an ongoing injection
- −Weight regain is common if stopped without a maintenance plan
- −Can reduce the effectiveness of the oral contraceptive pill, additional contraceptive precautions are needed, see below
Common side effects
If you take the oral contraceptive pill: Tirzepatide can reduce how well your body absorbs it, which may make it less effective at preventing pregnancy. Use an additional barrier method of contraception (such as condoms) for 4 weeks after starting Tirzepatide, and for 4 weeks after each dose increase. See our dedicated section on contraception below for more detail.
Liraglutide
GLP-1 receptor agonistSaxenda
An older, daily GLP-1 injection. Generally produces less weight loss than semaglutide or tirzepatide, but can be a reasonable option in specific circumstances.
Rough UK price: Roughly £180–£230 per month, generally similar to or more expensive than semaglutide despite typically producing less weight loss, as it requires daily rather than weekly pens.
How it works
Works in the same way as semaglutide, as a GLP-1 receptor agonist, but has a shorter duration of action and needs to be injected daily rather than weekly.
How to take it
- Injected subcutaneously once a day, at any time, with or without food.
- Given into the abdomen, thigh, or upper arm.
- Dose is increased gradually over around 5 weeks to the target dose.
- Store in the fridge.
Pros
- +Longer track record specifically for weight management than tirzepatide
- +Can be an option where semaglutide or tirzepatide are not suitable or not tolerated
Cons
- −Average weight loss of around 5 to 6% of body weight in trials, notably less than semaglutide or tirzepatide
- −Requires a daily injection rather than weekly
- −Similar side effect profile to other GLP-1 medications for less benefit
- −Generally not our first recommendation given the alternatives available
Common side effects
Orlistat
Lipase inhibitorXenical (prescription) / Alli (lower-dose, available over the counter)
The main oral, non-injectable option. Works in the gut rather than the brain, and has a very different, distinctive side effect profile.
Rough UK price: Roughly £30–£60 per month, the cheapest of the licensed weight loss medications.
How it works
Blocks around a third of the enzyme (lipase) that digests dietary fat in the gut, so that fat passes through the digestive system without being absorbed, rather than being taken up as calories.
How to take it
- Taken as a capsule up to three times a day, with each main meal that contains fat.
- Skip the dose if a meal is missed or contains no fat.
- A daily multivitamin is recommended, taken at a different time to Orlistat, as it can reduce absorption of fat-soluble vitamins (A, D, E, K).
Pros
- +Oral tablet, no injections required
- +By far the cheapest licensed option
- +Long track record and well understood safety profile
- +Available at a lower dose without a prescription (Alli)
Cons
- −Modest average weight loss compared with GLP-1 medications, typically 5 to 10% with sustained use alongside diet changes
- −Distinctive gastrointestinal side effects that are strongly linked to fat intake and can be socially difficult
- −Requires consistent low-fat eating to avoid side effects, which some people find restrictive
- −Reduces absorption of fat-soluble vitamins
- −If it causes severe diarrhoea, the oral contraceptive pill may not be absorbed properly, use additional contraceptive precautions if this happens
Common side effects
Naltrexone-Bupropion
Combination tabletMysimba
An oral combination tablet that acts on appetite regulation and reward pathways in the brain. An alternative for people who prefer not to inject, or where GLP-1 medications are not suitable.
Rough UK price: Roughly £90–£130 per month.
How it works
Combines naltrexone (used at low dose here, originally for addiction) and bupropion (an antidepressant), which together act on appetite centres and reward-related eating behaviour in the brain.
How to take it
- Taken as tablets, with the dose built up gradually over 4 weeks according to a specific schedule.
- Taken in the morning and evening, not with high-fat meals as this increases side effects.
- Should not be stopped abruptly if you have been on it for a while; discuss with us first.
Pros
- +Oral tablet, no injections required
- +A genuine alternative where GLP-1 medications are not suitable, not tolerated, or not preferred
- +Can help with food cravings and "reward-driven" eating specifically
Cons
- −Generally more side effects and more contraindications than GLP-1 medications
- −Not suitable for people with uncontrolled high blood pressure, a history of seizures, or various other conditions, we check this carefully at assessment
- −Average weight loss is lower than semaglutide or tirzepatide
Common side effects
Not suitable if you have uncontrolled high blood pressure, a history of seizures or eating disorders, or are taking certain other medications (including opioids). We screen carefully for these before prescribing.
Side effects to expect
Gastrointestinal side effects are by far the most common issue with weight loss medications, particularly GLP-1 and dual GIP/GLP-1 agonists. In clinical trials, nausea affected up to around 44% of people on semaglutide and a similar proportion on tirzepatide, most commonly during the dose-increasing (titration) phase, and it generally settles as the body adjusts.
Common, usually manageable
Nausea, vomiting, diarrhoea, constipation, and reflux affect a substantial minority of patients, particularly early on or after a dose increase. Eating smaller meals, eating more slowly, and avoiding high-fat or very rich food usually helps.
Rare, but serious
Pancreatitis occurs in fewer than 1 in 100 people on GLP-1 medications, but requires urgent attention. Gallstones and gallbladder disease are also more common with rapid weight loss of any kind, occurring in roughly 1.5 to 2 times as many people compared with those not on these medications.
GLP-1 and dual agonist medications slow stomach emptying, which is relevant if you are having a general anaesthetic. Current anaesthetic guidance generally recommends stopping these medications for a period before elective surgery to reduce the risk of aspiration; we will advise you on timing if this applies to you. These medications are not recommended in pregnancy, and are not currently recommended for use during breastfeeding.
Always tell your anaesthetist. Whether you are having a general anaesthetic, sedation, or any procedure with an anaesthetic team involved, make sure you tell them you are taking one of these medications, even if you have already followed our advice on stopping it beforehand. It changes how they manage your airway and reduces the risk of complications.
Sources: STEP and SURMOUNT trial safety data (NEJM); MHRA product information for Semaglutide, Tirzepatide, and Liraglutide.
Impact on contraception
If you use the oral contraceptive pill, it is important to be aware that weight loss injections can affect how well it works, and this is something we will always ask about at assessment.
Tirzepatide (Mounjaro) and the pill
Tirzepatide slows stomach emptying more than GLP-1-only medications, because it also acts on the GIP receptor. This can reduce how well your body absorbs an oral contraceptive pill, potentially making it less effective at preventing pregnancy.
If you take the pill and are prescribed tirzepatide, use an additional barrier method of contraception (such as condoms, a diaphragm, or a cap) for 4 weeks after starting tirzepatide, and for a further 4 weeks after each dose increase. This is the guidance also given by NHS England.
Semaglutide, liraglutide & other oral medications
Semaglutide and liraglutide also slow gastric emptying, though generally to a lesser degree than tirzepatide, and there is less specific guidance mandating additional contraceptive precautions with these medications. Orlistat does not affect gastric emptying, but if it causes severe diarrhoea, this can independently reduce absorption of the oral contraceptive pill, in the same way any significant gastrointestinal illness can, so additional precautions are recommended if this happens.
Non-oral contraception, such as the implant, hormonal or copper coil, or contraceptive injection, is not affected by any of these medications in the same way, as it does not rely on being absorbed through the gut. If you are relying on the pill and would prefer not to think about additional precautions, this may be worth discussing with us or your usual contraception provider.
Source: NHS England, weight management injections patient guidance.
Benefits beyond weight loss
A growing body of evidence shows these medications improve health outcomes beyond the number on the scale, which is part of why the evidence base for them has grown so quickly.
Cardiovascular disease
The SELECT trial (NEJM, 2023) followed over 17,000 adults with pre-existing cardiovascular disease and overweight or obesity, but without diabetes. Semaglutide reduced the risk of major adverse cardiovascular events (heart attack, stroke, or cardiovascular death) by 20% compared with placebo, a benefit that appeared to go beyond what weight loss alone would explain.
Type 2 diabetes
GLP-1 and dual GIP/GLP-1 medications were originally developed as diabetes treatments. They meaningfully lower HbA1c (a measure of average blood sugar) and reduce the risk of progressing from prediabetes to type 2 diabetes. The SURMOUNT trials showed that tirzepatide reduced progression to type 2 diabetes by around 90% in people with prediabetes and obesity over 3 years.
Blood pressure & heart failure symptoms
Weight loss with these medications is consistently associated with clinically meaningful reductions in blood pressure. The STEP-HFpEF trial found that semaglutide significantly improved symptoms, physical function, and exercise capacity in people with heart failure with preserved ejection fraction and obesity.
Sleep apnoea & joint pain
Clinical trials of tirzepatide (SURMOUNT-OSA) have shown significant reductions in the severity of obstructive sleep apnoea, in some cases resolving it. Weight loss of the scale seen with these medications is also strongly linked to reduced joint loading and less pain from osteoarthritis of the knee and hip.
Sources: SELECT trial (NEJM, 2023); SURMOUNT-1, SURMOUNT-OSA trials (NEJM); STEP-HFpEF trial (NEJM, 2023).
Red flags: when to contact us
Contact us or NHS 111 urgently, or attend A&E, if you experience:
- Severe, persistent abdominal pain, particularly if it spreads to your back (a possible sign of pancreatitis, a rare but serious side effect of GLP-1 medications)
- Pain in the upper right side of your abdomen, or yellowing of your skin or eyes (possible signs of gallstones or gallbladder problems)
- Persistent vomiting or an inability to keep fluids down, particularly with signs of dehydration (dizziness, dark urine, confusion)
- Signs of a severe allergic reaction: facial swelling, difficulty breathing, widespread rash or hives
- Significant low mood, hopelessness, or any thoughts of self-harm
- Symptoms of very low blood sugar if you are also taking insulin or sulfonylureas for diabetes (shaking, sweating, confusion)
- A fast, irregular heartbeat, chest pain, or fainting
Contact us at your next opportunity if:
- Side effects are troublesome or not settling after a couple of weeks at a new dose
- You are struggling to keep food or fluids down
- You think the medication is not working, or want to discuss adjusting the dose
- You want to stop, pause, or switch medication
- You are due to have surgery or a general anaesthetic
- You become pregnant, or are planning a pregnancy
How our service works
Alongside medication, we offer online courses covering nutrition, behaviour change, and building sustainable habits, whether or not you end up taking medication. If a prescription is appropriate for you, there are two ways we can get your medication to you.
A private prescription
We can issue you a private prescription that you can take to any pharmacy of your choosing, giving you the flexibility to shop around and compare prices yourself.
Medication via our affiliated pharmacy
Alternatively, we can arrange for your medication to be dispensed and posted to you directly by our affiliated pharmacy, in suitable packaging (including cold-chain packaging where required), by next-day, signed-for delivery.
Online courses
We offer online courses to support you alongside medication or lifestyle changes, covering the practical, day to day side of sustainable weight management. Ask us for details when you book.
Going through our affiliated pharmacy tends to work out cheaper than sourcing medication independently, but prices across the market fluctuate regularly, so we would still encourage you to shop around and compare. We will always be transparent with you about the cost of each option so you can decide what works best for you.
Follow up & monitoring
We tailor the follow up schedule to you rather than applying a single fixed template, based on how you are getting on, the medication and dose you are taking, and any side effects. As a general principle:
While establishing your dose
We ask for a monthly weight check while you are being titrated onto a new dose, so we can track your progress and response and adjust the plan if needed.
Once stable
Once you are established on a dose that is working well for you, review appointments become less frequent, though we will always agree the right interval with you individually.
We will never leave you without a plan for monitoring. If anything changes, whether that is your response to the medication, side effects, or your general health, please contact us so we can review your follow up schedule together.
Further reading
In addition to speaking with us, these official, independent sources provide reliable further information about each medication.
NHS England: Weight management injections
Official NHS overview of semaglutide and tirzepatide, including eligibility and contraception guidance
NHS medicines A–Z: Semaglutide
How it works, how to take it, and side effects
NHS medicines A–Z: Tirzepatide
How it works, how to take it, side effects, and contraception advice
NHS medicines A–Z: Liraglutide
How it works, how to take it, and side effects
NHS medicines A–Z: Orlistat
How it works, how to take it, and side effects
NICE: Naltrexone–bupropion (Mysimba) patient guidance
Official NICE guidance on the use of Mysimba for weight management