Before an operation or a procedure such as a colonoscopy, some medicines must be paused, some must be taken as usual, and some need a changed dose. Afterwards, pain relief, constipation and sleep raise new questions. This guide explains the usual rules and why they exist, so you know what to ask at your pre-admission appointment.
The short answer
- Never stop or change a medicine for surgery on your own. Bring a full list (or the boxes) to the pre-admission check and follow the written plan you are given.
- Commonly paused: blood thinners, some diabetes medicines (SGLT2 inhibitors such as Jardiance at least 3 days before), anti-inflammatories, and herbal supplements.
- Commonly continued, with a sip of water on the morning of surgery: most heart, blood pressure, thyroid, epilepsy, asthma and antidepressant medicines.
Why do medicines matter before surgery?
Anaesthesia and surgery stress the body in predictable ways: blood pressure swings, bleeding, a period without food, changes in blood sugar and slower bowels. Some medicines make these harder to manage. Blood thinners increase bleeding, some diabetes medicines can tip the body into ketoacidosis while you are fasting, and medicines that slow the stomach can leave food in it when you are put to sleep. Others are dangerous to stop: missing beta blockers, epilepsy medicines or steroids around surgery can cause serious problems.
That is why hospitals give each patient an individual list rather than a general rule. What follows is what that list typically contains, so you can prepare questions.
Which medicines are usually stopped, and which continued?
| Medicine group | Usual plan (your team decides) | Why |
|---|---|---|
| Warfarin | Usually stopped about 5 days before, with an INR check; sometimes “bridged” | Bleeding |
| Apixaban, rivaroxaban, dabigatran | Stopped 1–4 days before depending on the drug, kidney function and the operation | Bleeding |
| Clopidogrel, ticagrelor, low-dose aspirin | Case by case: never stop after a recent stent without the cardiologist | Bleeding vs stent clotting |
| SGLT2 inhibitors (Jardiance, Forxiga/Farxiga, Invokana) | Stop at least 3 days before (ertugliflozin 4 days) | Ketoacidosis while fasting |
| GLP-1 medicines (Ozempic, Mounjaro, Wegovy, Trulicity) | Increasingly continued; higher-risk patients may have a 24-hour liquid diet or a pause | Slower stomach emptying, risk of inhaling stomach contents |
| Metformin, sulfonylureas, insulin | Dose often held or reduced on the day; insulin adjusted, not stopped | Low blood sugar while fasting |
| NSAIDs (ibuprofen, naproxen, diclofenac) | Often stopped a few days before | Bleeding, kidney strain |
| ACE inhibitors and ARBs (ramipril, candesartan) | Often held on the morning of surgery | Low blood pressure under anaesthesia |
| Beta blockers, statins, thyroid, epilepsy, Parkinson’s medicines | Usually continued, including on the day | Stopping causes rebound problems |
| Steroids (prednisolone) | Continued; extra “stress” doses may be needed | The body can’t make enough cortisol under stress |
| Inhalers, eye drops, most antidepressants | Continued | Stopping causes more harm than continuing |
| Combined pill, HRT | Sometimes stopped 4 weeks before major surgery | Blood clot risk |
| Herbal and supplements (fish oil, ginkgo, garlic, ginseng, St John’s wort) | Usually stopped 1–2 weeks before | Bleeding, interactions with anaesthetics |
GLP-1 medicines and anaesthesia: semaglutide and tirzepatide slow stomach emptying. A 2024 guidance from US anaesthesia, gastroenterology and surgery societies supports continuing them for most patients, with a 24-hour clear-liquid diet for those at higher risk (for example during dose increases or with nausea and vomiting). Some hospitals still ask patients to pause a weekly injection a week before. Tell the team you use one, and follow their instruction.
Fasting rules and taking tablets on the day
Most hospitals follow the same basic fasting rules for adults having anaesthesia: no food for about 6 hours before, and clear fluids (water, black tea or coffee without milk, clear apple juice) until about 2 hours before. Some units now allow water closer to the procedure. Chewing gum and sweets also count as food in many hospitals.
The medicines you have been told to continue are taken at the usual time with a small sip of water, even when you are fasting. If you aren’t sure whether a tablet counts, take the pack with you and ask on arrival rather than skipping it. Specific questions are answered in Imodium before surgery, Colace before surgery and painkillers before wisdom teeth removal.
Before a colonoscopy or gastroscopy
- Iron tablets: usually stopped 5–7 days before a colonoscopy because they darken and thicken stool.
- Fibre supplements and anti-diarrhoeals (loperamide): stopped a few days before so the bowel prep can work.
- Blood thinners: as for surgery, depending on whether polyps may be removed.
- Diabetes medicines: doses change during the clear-fluid diet and prep; ask for a written plan.
- The pill: bowel prep can reduce absorption, so use extra contraception for the rest of that cycle as your leaflet advises.
- Other tablets: take them at least an hour before you start drinking the prep solution, or they may be flushed out.
Pain relief after surgery
Modern post-operative pain relief is built in layers: regular paracetamol as the base, an anti-inflammatory such as ibuprofen or celecoxib if your surgeon allows it, and a short course of an opioid (oxycodone, tramadol) only for breakthrough pain. Taking paracetamol and the anti-inflammatory regularly for the first few days, rather than waiting for pain to build, usually means less opioid is needed.
Some operations come with restrictions. After spinal fusion and some fracture repairs, surgeons may limit NSAIDs because of concern about bone healing; see ibuprofen after spinal fusion. After bariatric (weight-loss) surgery, NSAIDs are usually avoided long term because of ulcer risk. Opioids should be stopped as soon as possible, and leftover tablets returned to a pharmacy.
Constipation, nausea, itch and sleep
- Constipation: opioids, less movement and less food slow the bowel. A stimulant laxative (senna) with or without a softener, or macrogol, is often started with the opioid. Docusate alone is weak.
- Nausea: usually treated in hospital with ondansetron or similar. Eat small, plain meals.
- Itch: common with opioids. A non-sedating antihistamine may help; sedating ones like diphenhydramine can cause confusion in older people. See Benadryl after surgery.
- Sleep: broken sleep is normal for a week or two. Avoid combining sleeping aids with opioids unless your doctor has approved it.
Contact your surgical team or seek urgent care if after surgery you have increasing pain despite medicines, fever, a red or leaking wound, calf swelling, breathlessness or chest pain, black stools, no bowel movement and a swollen belly with vomiting, or you are very drowsy on painkillers.
Articles in this guide
Each article answers one specific question in depth.
- Can You Take Imodium Before Surgery?Loperamide before surgery is usually a question for your anaesthetist, and it must be stopped before bowel prep. When it matters and what to ask.
- Is It Safe to Take Colace (Docusate) Before Surgery?Docusate is a mild stool softener often given after surgery. Taking it before surgery, fasting rules, and better options for opioid constipation.
- Can I Take Benadryl After Surgery?Diphenhydramine helps itch from opioids but adds sedation and confusion risk, especially in older adults. When it's used and safer alternatives.
- How Long After Spinal Fusion Can You Take Ibuprofen?Many surgeons restrict NSAIDs after fusion because they may slow bone healing. Typical waiting periods, what the evidence shows and what to use instead.
- Pain Relief Before and After Wisdom Teeth RemovalParacetamol and ibuprofen are the backbone of pain relief after tooth extraction. Timing before surgery, sedation fasting and a recovery schedule.
Frequently asked questions about medicines and surgery
Can I take Tylenol after a colonoscopy?
Yes, paracetamol (Tylenol) is usually fine after a colonoscopy. If polyps were removed, you may be asked to avoid aspirin and other NSAIDs for a few days because of bleeding risk; follow the discharge sheet.
Can I take ibuprofen a week after a hip replacement?
Many surgeons use anti-inflammatories as part of pain relief after hip replacement, but some avoid them in patients with kidney problems or on blood thinners for clot prevention. Ask the orthopaedic team; don’t add ibuprofen to a blood thinner on your own.
Should I take my blood pressure tablets on the morning of surgery?
Most, yes, with a sip of water. ACE inhibitors, ARBs and diuretics are the ones most often held on the day. Your pre-admission instructions will say which.
How long before surgery should I stop supplements?
Typically 1–2 weeks for fish oil, ginkgo, garlic, ginseng, turmeric and St John’s wort. Tell the anaesthetist about all of them, including vitamins and anything bought online.
Sources and further reading
- American Society of Anesthesiologists – Multi-society GLP-1 guidance (2024)
- Farxiga (dapagliflozin) US prescribing information – stop at least 3 days before scheduled surgery
- Centre for Perioperative Care (UK) – Guidance for patients
- Royal College of Anaesthetists – Patient information
- Australian and New Zealand College of Anaesthetists – Patient information
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