Why the source matters more than the price
Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines. Buying from the wrong seller carries real risk, because you cannot be sure what is in the pen, how it has been stored, or whether anyone checked that treatment is suitable for you.
The Medicines and Healthcare products Regulatory Agency (MHRA) warned in July 2026 that prescription weight loss medicines are being advertised illegally on social media, alongside quick-fix slimming claims. Its advice is that if you are not eligible for a prescription, you should not buy from unregulated websites or social media sellers.
The rest of this guide covers how to check a provider, what a safe prescribing process should look like, the warning signs of a bad seller, and what to do if something goes wrong.
How to check a pharmacy or clinic is registered
Check the pharmacy as well as the pharmacist, and check before you pay.
- In Northern Ireland: the Pharmaceutical Society of Northern Ireland (PSNI) regulates pharmacists and pharmacies. Search its register at registers.psni.org.uk for both the pharmacist and the premises. The register has displayed a "searching issue" notice, so if a search fails, try again later and ask the provider for its registration details in writing.
- In Great Britain: the General Pharmaceutical Council (GPhC) regulates pharmacies and pharmacists. The MHRA advises checking that the pharmacy is registered with the GPhC.
- Independent clinics in Northern Ireland: the Regulation and Quality Improvement Authority (RQIA) regulates independent healthcare. Check the clinic on the RQIA register.
Be wary of providers that describe themselves as "CQC regulated". The Care Quality Commission regulates services in England, not in Northern Ireland, so the claim tells you little about a service based here.
What a safe prescribing process should look like
In February 2025 the GPhC updated its guidance for online pharmacies and added GLP-1 medicines to its list of high-risk medicines. Under that guidance, as reported in the news coverage at the time, the prescriber must independently check your weight, height and/or body mass index (BMI) before prescribing.
Acceptable routes include a video consultation, reviewing your clinical records, or contacting your GP. Online questionnaires and phone calls alone are not enough. The guidance also expects the prescriber to ask for your GP details and your consent to contact your GP.
These rules were written for pharmacies regulated by the GPhC. We have not confirmed an equivalent rule from the PSNI for pharmacies in Northern Ireland, so ask any Northern Ireland provider directly how it checks your BMI.
The licence covers adults with a BMI of 30 or above, or 27 to under 30 with a weight-related condition. A provider that offers treatment to people outside those criteria, without a clear clinical reason, is a warning sign. In April 2026 the GPhC reported 1,307 concerns about weight management medicines over January 2024 to December 2025, and the most common problem was inadequate checking of BMI.
Warning signs of an unsafe seller
- Prices that seem too good to be true, or offers built around the medicine itself.
- Claims of "miracle results" or "quick fixes".
- An offer of a pen with no prescription or consultation. The MHRA's advice is to walk away.
- Sales through social media or messaging apps, or sites with no registered pharmacy or clinic details.
- No health questions, and no contact with your GP or a prescriber.
- Requests for photos of yourself in place of a measured weight and height.
The MHRA has also warned about fake Mounjaro 15 mg KwikPen pens dispensed by a pharmacy in Birmingham. Testing found tirzepatide in the contents, but sterility could not be confirmed. A pen can look genuine and still be unsafe.
Retatrutide is not authorised for use in the UK. The MHRA says anyone selling it is doing so illegally, so treat any offer of it as a warning sign.
What to do if you think a pen is fake or you have a serious side effect
Do not use a pen that you think may be fake without advice first. Contact a pharmacist or your prescriber as soon as you can, keep the pen and its packaging, and tell them what happened.
Pancreatitis is the serious side effect the MHRA has most recently highlighted. In January 2026 it strengthened the warnings for GLP-1 and GLP-1/GIP medicines, including tirzepatide and semaglutide. Seek urgent medical attention for severe, persistent abdominal pain that may spread to your back, especially if it comes with nausea or vomiting. Do not restart the medicine if pancreatitis is confirmed.
Report suspected side effects through the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. For more on what to expect and when to get help, read our guide to side effects.
Questions to ask before you order
- Is the pharmacy registered with the PSNI or the GPhC, and what is its registration number?
- Who is the prescriber, and what professional registration do they hold?
- How do you check my BMI and weight, and will you contact my GP?
- What happens if I am not suitable for treatment?
- Who do I contact about side effects, and how do I reach them out of hours?
- How is the medicine stored and delivered, and what happens if a pen arrives damaged?
If you are looking at a pharmacy in Great Britain, check its delivery terms for Northern Ireland before you order. Some GB pharmacies say they do not deliver here, and we have not confirmed the reason, so ask them directly.
Before you choose a provider, it helps to read our eligibility checker and comparison guide. Remember that a prescriber decides whether treatment is suitable and which dose you should use.