GLP-1 receptor agonists slow gastric emptying. That is part of how they work — food stays in the stomach longer, you feel full for longer.
Under general anaesthesia or deep sedation, a stomach that has not emptied when it was expected to is a problem. There is a risk of pulmonary aspiration: stomach contents entering the airway and lungs. The MHRA issued a drug safety update on exactly this for GLP-1 and dual GIP/GLP-1 receptor agonists.
What UK Guidance Says
The headline point catches people out, because it is the opposite of what most assume. Current UK multidisciplinary guidance is that patients taking these medicines should generally continue them before surgery, with full risk assessment, and with anaesthetic techniques adapted to reduce the aspiration risk.
In other words, the answer is not "stop taking it a week before". The answer is "make sure the team knows, so they can plan around it". Do not stop your treatment without discussing it with your doctor.
Why Private Prescriptions Get Missed
This is the practical failure point. A GLP-1 obtained privately online may not be in your GP record. The pre-operative assessment team works from that record and from what you tell them.
If nobody has told them, nobody knows. The medicine does not become less relevant because you paid for it yourself.
Tell them:
- Which medicine you take — name it specifically
- The dose
- When you last took it, which for a weekly injection may be days ago and still relevant
- Whether you have recently increased the dose
Which Procedures This Applies To
Anything involving general anaesthesia or deep sedation. That includes procedures people do not think of as surgery — endoscopy, colonoscopy, some dental work under sedation, and various day-case procedures.
It also matters for emergency care. If you are admitted acutely and may need a procedure, this is information the team needs early rather than at the door of theatre.
What Might Change
Depending on your assessment, the team may adjust:
- Fasting instructions — potentially a longer period, or clear fluids only for longer
- The anaesthetic technique, to reduce aspiration risk
- Pre-procedure assessment, which may include an ultrasound scan of the stomach in some centres
These are their decisions to make, and they can only make them with the information.
Other Professionals Who Should Know
The same logic extends further than surgery. A GLP-1 is worth declaring to:
- Your GP, even if the prescription is private
- Any hospital team treating you
- A dentist planning sedation
- A pharmacist checking for interactions
- A maternity team, since these medicines are not used in pregnancy
The Broader Point
Private prescribing is legitimate and often the only realistic route given NHS waits. What it should not create is a medicine that exists outside your medical record. The GPhC now expects online pharmacies to offer two-way communication with a prescriber and to verify what they are told — but nothing in that system tells your anaesthetist. Only you can do that.