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I'm already taking a GLP-1. What should I check?

Four checks for anyone already on semaglutide (Wegovy, Ozempic), tirzepatide (Mounjaro) or another GLP-1, plus what to read next.

GLP Guidebook teamUpdated 12 Oct 20264 min read16 sourcesWritten from published sources
The short answer

Check four things. First, that a healthcare professional prescribed it after a proper consultation, and that your pharmacy is registered. Second, that your pen looks and works as it should, because fakes have been found in the UK. Third, which side effects need a call to your GP or 111, and which need 999. Fourth, plan a review at about 6 months.

Read this page first. It covers the checks that matter once you've started: your prescription, fake pens, side effects and when to review how it's going. At the end, three guides take you further, in order.
On this page
  1. Check your prescription
  2. Check your pen is genuine
  3. Side effects to watch
  4. Your 6-month review
  5. What to read next
  6. Sources

1. Did my prescription come the right way?

All GLP-1 medicines are prescription-only. On the NHS that means your GP or a specialist service; privately, a doctor or another registered prescriber, such as a pharmacist, after a proper consultation.

The MHRA, the UK medicines regulator, says a consultation with a healthcare professional must happen before a private prescription is issued.1 For weight-loss medicines, the General Pharmaceutical Council (GPhC) also says an online prescriber can't rely on a questionnaire alone. They must check your weight, height or BMI themselves: by video, in person, from your medical records or by contacting your GP.2,3

You can check that a pharmacy in Great Britain is registered on the GPhC website. For Northern Ireland, use the Pharmaceutical Society of Northern Ireland (PSNI).1

Red flags

  • You never spoke to anyone, only filled in a form. The GPhC says that isn't enough for weight-loss medicines.2
  • Your weight was checked only by a phone call, or only by a photo you sent in for a first supply. The GPhC says neither is enough on its own.3
  • "No prescription needed", or a seller in a beauty salon or on social media. The MHRA says not to buy from them.1
  • A powder in a vial that you mix with liquid. The MHRA says these are not authorised; genuine GLP-1s come as pre-filled pens or tablets.1
  • Retatrutide, sold as a newer "jab". It is unlicensed in the UK, and the MHRA has seized illegal retatrutide pens.4

2. Is my pen genuine?

Fake pens have been found in the UK, including one supplied through a UK online pharmacy.

  • Mounjaro 15 mg, February 2026. A falsified KwikPen 15 mg was supplied through one online pharmacy in the UK, labelled with batch D873576. It was noticed because the dose knob came off while in use.5
  • Ozempic and Saxenda, October 2023. The MHRA warned about fake pens found in the UK.6
  • Illegal supply. In October 2025 the MHRA found what it called the first illegal factory for weight-loss medicine in the UK, seizing more than 2,000 unlicensed retatrutide and tirzepatide pens.4

Check the batch number on your pen and box. If anything looks or works differently from usual, show it to your pharmacist. If you suspect a pen isn't genuine, the MHRA asks you to report it to the Yellow Card scheme.1 Guide 6 covers fakes and safety alerts.

Don't stop or switch on your own. If you're worried about your pen, ask your prescriber or pharmacist what to use instead and how to restart.

3. Which side effects should I watch for?

Stomach upsets are common early on and usually fade.7 A few symptoms need help fast.

Get help now: call 999 or go to A&E if you have:
  • Possible pancreatitis (an inflamed pancreas): severe stomach pain that won't go away, sometimes spreading to your back, with or without vomiting.8
  • Signs of a serious allergic reaction: swelling of your face, lips, tongue or throat; trouble breathing; fainting; or a very fast heartbeat.9
  • Signs of very low sugar, like confusion or drowsiness, if you also take insulin or a sulfonylurea (an older diabetes tablet such as gliclazide).9
Call your GP or prescriber soon, or 111 if it's urgent, if you have:
  • Possible gallbladder problems: pain in the upper stomach, yellow skin or eyes, fever, or pale clay-coloured stools.9
  • Vomiting or diarrhoea that stops you keeping fluids down.9
  • Changes in your vision, if you have diabetes.9
  • Possible thyroid problems: a lump in your neck, hoarseness, or trouble swallowing.8
111 covers England, Scotland and Wales. Northern Ireland has no 111 service: call your GP surgery, which will direct you to out-of-hours care.10

Report a side effect. Tell your prescriber first. You can also report it yourself to the MHRA's Yellow Card scheme, online at yellowcard.mhra.gov.uk or in the Yellow Card app, or by phone on 0800 731 6789 (Monday to Friday, 9am to 5pm).11,12

On Mounjaro and taking the contraceptive pill? The MHRA advises adding a barrier method such as condoms for 4 weeks after starting and for 4 weeks after each dose increase, or switching to a non-pill method such as a coil or implant.1 Having an operation? Tell your doctor you take a GLP-1, and don't stop it without talking to them first.1

4. When should I review how it's going?

At about 6 months, or sooner if your prescriber suggests it.

NICE, the body that writes guidance for the NHS in England, says to consider stopping semaglutide (Wegovy) if less than 5% of your starting weight is lost after 6 months.13 For tirzepatide (Mounjaro), if less than 5% is lost after 6 months on the highest dose you can manage, it says to decide whether to carry on, weighing the benefits and risks.14 For someone who started at 90 kg (14 st 2 lb), 5% is 4.5 kg (about 10 lb).

If you have diabetes, NICE says HbA1c (a blood test of your average sugar over 2 to 3 months) is checked every 3 to 6 months until it's stable, then every 6 months.15

Paying privately and hoping to switch to the NHS? Your GP can assess you, but you must meet the NHS criteria at the time you're assessed.16

Take this to your review

  • The brand, strength and dose you're on, and the batch number
  • Your weight and waist notes since you started
  • Any side effects, and when they happen
  • All your other medicines, including herbal remedies and anything bought online
  • Your questions about the long term, and about stopping
Life on a GLP-1StoppingBefore you see a GP

What to read next, in order

These three guides go deeper. Each one ends with a link to the next, so you can read them one after another.

  1. 1Side effects and risksGuide 5 of 9DecideWhat's normal in the first weeks, what isn't, and what helps.
  2. 2Life on a GLP-1Guide 8 of 9Live with itEating enough protein, missed doses, storing pens and travelling, Ramadan and fasting.
  3. 3Stopping and the long termGuide 9 of 9Live with itWhat happens if you stop, and how to plan for the long term.
Was this page easy to understand?

Sources

  1. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know. GOV.UK, updated 5 February 2026. Sections on where to find GLP-1 medicines, contraception and pregnancy, surgery, and reporting. Link
  2. General Pharmaceutical Council. Online pharmacies to strengthen safeguards to prevent unsafe supply of medicines (guidance for pharmacies providing services at a distance, 4 February 2025). Link
  3. General Pharmaceutical Council. Providing weight management services: FAQs ("Verifying information through a phone call would not be appropriate"; "It would also not be appropriate to solely use a photograph or pre-recorded video supplied by the person"). Checked 12 October 2026.
  4. MHRA. MHRA smashes major illicit weight loss medicine production facility in record seizure. GOV.UK, 24 October 2025. Link
  5. MHRA. Drug Safety Update: falsified Mounjaro (tirzepatide) KwikPen 15mg pre-filled pens. 24 February 2026. Link
  6. MHRA. MHRA warns of unsafe fake weight loss pens. GOV.UK, 26 October 2023. Link
  7. Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM, 2021;384:989–1002. 1,961 adults without diabetes, 68 weeks. DOI
  8. Novo Nordisk. Wegovy (semaglutide) US prescribing information, revised June 2026. Sections 1, 2.2, 5.2, 5.3, 5.5, 8.3, 17. (US label.) PDF
  9. Novo Nordisk. Ozempic (semaglutide) injection, US prescribing information and Medication Guide, revised May 2026. Sections 4, 5.3, 5.5, 5.6, 7.2, 8.5. (US label.) PDF
  10. NHS. When to use 111 (England); NHS 24 (Scotland) and NHS 111 Wales run the 111 service in those nations; Northern Ireland has no 111 service. Checked 12 October 2026. Link
  11. MHRA. Yellow Card scheme: report a side effect online or in the Yellow Card app. Link
  12. NHS inform (Scotland). Yellow Card scheme reporting by phone, 0800 731 6789, Monday to Friday 9am to 5pm. Checked 12 October 2026.
  13. NICE. Semaglutide for managing overweight and obesity. Technology appraisal TA875, recommendation 1.2. Declared interests: some invited clinical experts declare fees or grants from Novo Nordisk and Eli Lilly (NICE's own register of interests for this appraisal). Link
  14. NICE. Tirzepatide for managing overweight and obesity. Technology appraisal TA1026, recommendation 1.2. Link
  15. NICE. Type 2 diabetes in adults: management. NICE guideline NG28, last updated 18 February 2026. Recommendation 1.5.1. Link
  16. NHS Central East Integrated Care Board (Hertfordshire and West Essex). Tirzepatide (Mounjaro) for weight management: information for patients (private prescriptions and NHS eligibility). Checked 12 October 2026.

Last checked 12 Oct 2026 · Next review due Jan 2027

How this page was made. Written by the GLP Guidebook team from the sources above: drug labels, published trials, NICE guidance, and official MHRA, GPhC and NHS pages. It's general information, not medical advice. Talk to your GP or another qualified prescriber before starting, stopping or changing any medicine. How we write