What is Semaglutide? How It Works, Side Effects & What to Expect

What is Semaglutide?

Semaglutide is a type of medicine called a GLP-1 receptor agonist. It can help you lose weight when combined with a healthy diet and exercise.

Semaglutide is sold under the brand name Wegovy for weight loss and as Ozempic (injections) or Rybelsus (tablets) to help manage type 2 diabetes. It is available as a Prescription Only Medication (POM).

What is a GLP-1 receptor agonist?

A GLP-1 receptor agonist is a drug that mimics a hormone in your body called glucagon-like peptide 1 (GLP-1). This hormone helps control your blood sugar, slow your digestion and control your appetite.

GLP-1 receptor agonists target receptors in your brain and gastrointestinal tract (gut). They work in four main ways:

• Stimulates your pancreas to produce insulin to lower your blood sugar
• Prevents your liver from releasing sugar into your blood
• Delays stomach emptying, meaning you feel full faster and stay full for longer
• Suppresses your appetite and reduces cravings and ‘food noise’ [8]

What are the benefits of semaglutide?

Semaglutide is a weight loss medicine that offers many benefits to people who are overweight or obese and/or have type 2 diabetes.

Benefits of semaglutide include:

• Significant weight loss which reduces your risk of many serious health conditions, including type 2 diabetes, heart disease, high blood pressure, stroke, osteoarthritis and some cancers including certain obesity-related cancers such as colorectal, breast, and endometrial cancer (based on evidence linking obesity reduction to reduced cancer risk).
• Improved blood sugar control in people with type 2 diabetes
• Reduced risk of heart attack and stroke [6]
• Reduced blood pressure and blood fats like cholesterol and triglycerides [1]
• Clinical trials such as the FLOW trial [5] have found that semaglutide slows the progression of chronic (long-term) kidney disease in patients with type 2 diabetes

How effective is semaglutide for weight loss?

Semaglutide is a highly effective weight loss medication, producing an average weight loss of nearly 15% body weight over 68 weeks, as was demonstrated in a series of clinical trials known as the STEP (Semaglutide Treatment Effect in People with Obesity) [1,2,3,4] trials.

During the clinical trials, different groups of participants were given weekly injections of 2.4 mg of semaglutide or a placebo (fake treatment).

The main findings of the trials are as follows:

Who can take semaglutide?

Whether you are eligible to take semaglutide for weight loss in the UK depends on whether you get it on the NHS or privately. The criteria for semaglutide on the NHS are stricter and include: [7]

• A body mass index (BMI) of 35 or above, or 30 or above with a weight-related health condition
• A BMI of 27.5 or 32.5 (depending on other factors) and are of Asian, Chinese, Middle Eastern, Black African, or African-Caribbean descent
• In some cases, a BMI of 27 or above, and have peripheral arterial disease (PAD), or have had a heart attack or stroke

If you do not meet the NHS criteria, you may be able to get semaglutide privately at a GPhC-regulated pharmacy like Pharmacy Online.

Please note: NHS access to semaglutide is expanding and eligibility criteria may change. The information above reflects current guidance at the time of writing. For the most up-to-date NHS criteria, visit NICE TA875 or NHS England's weight management pages.

Who can’t take semaglutide?

Semaglutide isn’t suitable for everyone. Tell your doctor or pharmacist about any medical conditions or allergies you have and any medicines you take regularly, including over-the-counter medicines and supplements.

Semaglutide is not safe for you if:

• You are pregnant or breastfeeding
• You are allergic to semaglutide or other GLP-1 receptor agonists
• You are taking another GLP-1 receptor agonist
• You have a history of pancreatitis
• You, or a close relative, has a history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2)[8]

Semaglutide may not be suitable for you if you have:

• Type 1 diabetes
• Diabetic retinopathy
• Some types of bowel disease
• You have severe kidney or liver problems — discuss with your doctor before starting treatment

How do you take semaglutide?

Semaglutide is available as a weekly injection or a daily tablet. Your healthcare provider will help you decide on the best method for you. Read on to understand the difference between oral and subcutaneous semaglutide.

Semaglutide injections

Semaglutide injections are taken once a week as a subcutaneous (under the skin) injection.

Your healthcare provider will show you how to give your semaglutide injection correctly. Instructions will also be in the patient information leaflet that comes with your medicine. Ask your doctor or pharmacist if you have any questions.

• Take your semaglutide injection on the same day of the week. You can take it at any time of the day, with or without food.
• Give your injection in your abdomen (at least 2 inches away from your belly button), thighs, or upper arm. Rotate the injection site each week.
• Wash and dry your hands thoroughly before giving your injection
• Clean the area you are injecting with an alcohol swab before giving your injection. Do not inject into sore, broken or damaged skin.
• To give your semaglutide injection, pinch the skin, insert your needle at a 90-degree angle and push the plunger down slowly.
• Store your Wegovy pens in the refrigerator between 2°C and 8°C. Do not freeze. Once removed from the fridge, use within 6 weeks.
• Dispose of your used pens and needles safely in an approved sharps container. For full guidance visit NHS sharps disposal guide.

Semaglutide tablets

Semaglutide tablets are now approved as a weight loss treatment in the UK. They will be available from Pharmacy Online from July 2026, and we are currently taking pre-orders for the Wegovy pill.

To take semaglutide tablets:

• Take your tablet once a day, first thing in the morning on an empty stomach with a small amount of water
• Swallow your tablet whole (do not crush, chew, dissolve or cut it)
• Wait for at least 30 minutes before eating, drinking, or taking any other medicines

Semaglutide dosage

The dose of semaglutide is gradually increased every four weeks until you reach your maintenance dose. Your dose will depend on how much weight you lose and any side effects.

Take your semaglutide exactly as prescribed and do not adjust your dose unless your healthcare provider tells you to.

Semaglutide injections dosage

The starting dose for semaglutide injections is 0.25 mg once a week for four weeks. This is increased every four weeks to 0.5 mg, 1 mg, and 1.7 mg until you reach the standard maintenance dose of 2.4 mg once a week.[8]

In January 2026, the MHRA approved a higher-dose Wegovy pen containing 7.2 mg of semaglutide. This is now the maximum licensed weekly dose and may be suitable for people who have not achieved sufficient weight loss at 2.4 mg. The new 7.2 mg pen delivers the full dose in a single injection. [10]

In the STEP-UP clinical trial, participants taking 7.2 mg lost an average of 20.7% of their body weight, compared to around 14.9% at the standard 2.4 mg dose.[12]

One of our registered pharmacists can advise whether a higher dose is appropriate for you based on your progress and tolerance.

Semaglutide tablets dosage

Oral semaglutide is taken once a day and follows a gradual dose escalation schedule to help your body adjust to the medication and reduce the chance of side effects.

The starting dose is 1.5 mg once daily for the first month. This increases to 4 mg in month two, then 9 mg in month three. [9]

If you are tolerating the medication well and need further weight loss, your dose will increase to the maximum maintenance dose of 25 mg once daily from month four onwards. You should spend a minimum of one month at each dose level before increasing.

If you are switching from Wegovy injections (2.4 mg once weekly), your pharmacist or doctor may start you directly on the 25 mg tablet without the need to titrate up from the lowest dose.

Take your semaglutide exactly as prescribed. Do not adjust your dose or skip your titration steps without speaking to a healthcare provider first.

What to do if you miss a dose

Semaglutide injections

If you miss your weekly injection, take it as soon as you remember — but only if it is within 5 days of your missed dose. After that, carry on with your usual injection day as normal. [8]

If more than 5 days have passed since your missed dose, skip it entirely and take your next injection on your regularly scheduled day. Do not take a double dose to make up for a missed one.

If you have missed several doses in a row, speak to your doctor or pharmacist, as you may need to restart at a lower dose.

Semaglutide tablets

If you miss your daily tablet, skip the missed dose and take your next tablet the following day at your usual time. [9] Do not take two tablets on the same day to make up for a missed dose.

What happens if you stop semaglutide?

Semaglutide is a long-term treatment, and most people regain weight if they stop taking it. Clinical evidence from the STEP trials confirms this: in the STEP 4 trial, participants who stopped semaglutide after 20 weeks regained an average of 6.9% of their body weight over the following year, while those who stayed on the medication continued to lose weight. [4]

A separate extension of the STEP 1 trial found that participants regained around two-thirds of the weight they had lost within one year of stopping.[13]

This does not mean you have to stay on semaglutide indefinitely, but it does mean that stopping should be a considered decision made with your healthcare provider — not something to do suddenly or without a plan.

If you are thinking about stopping, we can help you weigh up the options, including whether you have reached a stable weight, whether lifestyle changes can support you off medication, and whether treatment should continue.

Semaglutide side effects

Like all medicines, semaglutide can cause side effects in some people. Most side effects are mild and improve as your body adjusts to the medication. If you have side effects that are bothering you, getting worse, or not getting better, make an appointment with your GP.

Common side effects of semaglutide include:

• Nausea (feeling sick)
• Vomiting (being sick)
• Abdominal pain (stomach ache)
• Diarrhoea
• Constipation
• Fatigue
• Hair loss

Rare, but serious side effects of semaglutide include:

• Severe allergic reaction (anaphylaxis)
• Changes to your vision
• Gallbladder problems, including gallstones (cholelithiasis) — symptoms include severe upper abdominal pain, nausea, and vomiting. Contact your doctor if you experience these symptoms[8,9]
• Acute pancreatitis
• Hypoglycaemia (low blood sugar) [8,9]

▼ This medicine is subject to additional monitoring. This will allow quick identification of new safety information. You can help by reporting any side effects you may get. See how to report side effects.

Semaglutide and other medications

Before starting semaglutide, tell your doctor or pharmacist about all medicines you take, including prescription medicines, over-the-counter medicines, vitamins, and herbal supplements.

The most important interactions to be aware of are:

• Insulin and sulfonylureas (diabetes medicines): Taking semaglutide alongside insulin or sulfonylureas (such as glipizide or gliclazide) increases your risk of hypoglycaemia (low blood sugar). Your doctor may reduce your insulin or sulfonylurea dose when you start semaglutide.
• Levothyroxine (thyroid medication): Semaglutide can increase the amount of levothyroxine absorbed by your body. If you take levothyroxine, your doctor may want to monitor your thyroid levels more closely.[9]
• Warfarin and blood thinners: The formal interaction study with warfarin showed no clinically relevant effect on INR (a measure of how quickly blood clots). However, as a precaution, your doctor may monitor your INR more frequently when you start semaglutide, particularly if you take acenocoumarol or other coumarin-based blood thinners.[8,9]
• Other oral medicines: Semaglutide slows down how quickly your stomach empties, which can affect how your body absorbs other medicines taken by mouth. If you take semaglutide tablets, you must wait at least 30 minutes after taking semaglutide before taking any other oral medication — including other tablets, capsules, or liquid medicines. Taking other medicines at the same time also reduces how well semaglutide itself is absorbed, so the 30-minute gap protects both.
• The contraceptive pill: Clinical studies found that semaglutide does not reduce the effectiveness of the contraceptive pill. However, because semaglutide must not be used during pregnancy, women of childbearing potential are recommended to use contraception throughout treatment. If you take the pill, follow the 30-minute waiting rule above after taking your semaglutide tablet.[8]

If you are unsure whether any of your medicines could be affected, speak to your pharmacist before starting semaglutide.

Semaglutide vs Tirzepatide

Semaglutide and tirzepatide (Mounjaro) are both effective weight loss drugs, but there are some differences between the two which can be seen in the table below. Our GPhC-registered pharmacists will help you decide which medicine is best for you.

Semaglutide and lifestyle

Semaglutide is licensed as an adjunct to a reduced-calorie diet and increased physical activity — meaning it is designed to work alongside lifestyle changes, not instead of them. [7]

Clinical evidence shows that people lose significantly more weight when they combine semaglutide with dietary and lifestyle support than with either approach alone.

Diet

You do not need to follow a specific named diet while taking semaglutide, but a reduced-calorie approach is part of the licensed treatment. In practice, this means eating slightly less than you currently do, with a focus on nutritious, balanced meals. Because semaglutide reduces appetite and slows stomach emptying, many people find it easier to eat smaller portions and feel satisfied with less food.

Some practical tips:

• Prioritise protein at each meal to help preserve muscle mass and keep you feeling fuller for longer
• Eat regular meals rather than skipping them, as irregular eating can increase nausea
• Stay well hydrated — dehydration can worsen side effects and is a risk if nausea or diarrhoea occurs
• Avoid large, high-fat meals, particularly in the early weeks of treatment, as these can worsen gastrointestinal side effects

If you are unsure how to adjust your diet, ask your GP or weight management service for a referral to a dietitian.

Exercise

Increased physical activity is a core part of semaglutide treatment. Aim to build regular movement into your routine — both aerobic exercise (such as walking, swimming, or cycling) and resistance training (such as weights or bodyweight exercises).

Resistance training is particularly important. Semaglutide promotes loss of both fat and muscle mass. Incorporating resistance exercise helps preserve muscle strength during weight loss, which matters for long-term metabolic health and physical function. [7,8]

If you are new to exercise or have any health conditions that affect your ability to be active, speak to your healthcare provider before starting a new exercise programme.

Alcohol

There is no formal interaction between semaglutide and alcohol in the Wegovy prescribing information, and alcohol is not prohibited while taking semaglutide. However, there are a few things worth being aware of.

Nausea is one of the most common side effects of semaglutide, particularly during the dose escalation period. Alcohol can worsen nausea and other gastrointestinal symptoms, so drinking — especially in larger amounts — may make side effects harder to tolerate.

If you have type 2 diabetes, alcohol can cause unpredictable changes in blood sugar, including hypoglycaemia (low blood sugar), particularly if you drink on an empty stomach or after exercise. This risk is greater if you are also taking insulin or sulfonylureas alongside semaglutide.

Both heavy alcohol use and semaglutide are independently associated with an increased risk of pancreatitis. Heavy drinking should be avoided by everyone on this medication. [8,9]

Most people taking semaglutide can drink in moderation without problems. If you have any concerns, speak to your doctor or pharmacist.

How much does semaglutide cost?

The cost of semaglutide depends on the dose and whether you are taking injections or tablets.

Semaglutide injections:

At Pharmacy Online, we offer semaglutide injections under the brand name Wegovy. Current prices are as follows:

*Prices correct at time of writing. Subject to change.

Semaglutide tablets

Semaglutide tablets will be available from Pharmacy Online from early July 2026. Pre-orders are now open. Current prices are as follows:

*Prices correct at time of writing. Subject to change.

The Bottom Line

Semaglutide is one of the most effective weight loss treatments available in the UK, with clinical trials showing up to 20.7% body weight loss at the highest dose. It works best alongside a healthy diet and exercise, and most people regain weight when they stop — so it is a long-term commitment, not a quick fix. Side effects are common early on but usually improve with time.

Is semaglutide right for you?

Semaglutide may be right for you if you have a BMI of 30 or above and have struggled to lose weight through lifestyle changes alone, or if you have a weight-related health condition such as type 2 diabetes or cardiovascular disease.

It is not suitable for everyone, so a clinical assessment is essential. Our registered pharmacists at Pharmacy Online can assess your suitability and, if appropriate, prescribe semaglutide.

This article was written by Claudia Jackson RN Freelance Health Content Writer.

This article was medically reviewed by Umar Razzaq - Clinical Pharmacist at Pharmacy Online (GPhC: 2064448). Last reviewed: 30 June 2026

References

1.Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. https://doi.org/10.1056/NEJMoa2032183

2. Davies M, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). Lancet. 2021;397(10278):971-984. https://doi.org/10.1016/S0140-6736(21)00213-0

3. Wadden TA, et al. Effect of Subcutaneous Semaglutide vs Placebo as an Adjunct to Intensive Behavioural Therapy on Body Weight in Adults With Overweight or Obesity (STEP 3). JAMA. 2021;325(14):1403-1413. https://doi.org/10.1001/jama.2021.1831

4. Rubino DM, et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity (STEP 4). JAMA. 2021;325(14):1414-1425. https://doi.org/10.1001/jama.2021.3224

5. Perkovic V, et al. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes and Moderate-to-Severe Chronic Kidney Disease (FLOW). N Engl J Med. 2024;391:1757-1769. https://doi.org/10.1056/NEJMoa2403347

6. Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232. https://doi.org/10.1056/NEJMoa2307563

7. National Institute for Health and Care Excellence. Semaglutide for managing overweight and obesity. Technology appraisal guidance TA875. NICE; 2023. https://www.nice.org.uk/guidance/ta875

8. Novo Nordisk Limited. Wegovy 0.25 mg FlexTouch solution for injection in pre-filled pen: Summary of Product Characteristics. Electronic Medicines Compendium; updated May 2026. https://www.medicines.org.uk/emc/product/13799/smpc

9. Novo Nordisk Limited. Wegovy 25 mg tablets: Summary of Product Characteristics. Electronic Medicines Compendium; updated June 2026. https://www.medicines.org.uk/emc/product/102347/smpc

10. Medicines and Healthcare products Regulatory Agency. Single-dose 7.2 mg semaglutide (Wegovy) pen approved to treat adult patients with obesity. GOV.UK; April 2026. https://www.gov.uk/government/news/single-dose-72mg-semaglutide-wegovy-pen-approved-to-treat-adult-patients-with-obesity

11. Medicines and Healthcare products Regulatory Agency. First GLP-1 tablet for weight loss approved in the UK. GOV.UK; June 2026. https://www.gov.uk/government/news/first-glp-1-tablet-for-weight-loss-approved-in-the-uk

12. Wadden TA, et al. Once-weekly semaglutide 7.2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. Lancet Diabetes Endocrinol. 2025. https://doi.org/10.1016/S2213-8587(25)00226-8

13. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. https://doi.org/10.1111/dom.14725

14. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. https://doi.org/10.1056/NEJMoa2206038

15. NHS England. Weight management injections. https://www.england.nhs.uk/ourwork/prevention/obesity/medicines-for-obesity/weight-management-injections/