GLP-1s Before Knee or Hip Replacement: BMI Cutoffs and the Pre-Op Hold
If your surgeon wants your BMI under 40 before a knee or hip replacement, a GLP-1 can plausibly get many men there within months: in trial run-in phases, people lost an average of about 10% of body weight in 20 weeks on semaglutide and about 21% in 36 weeks on tirzepatide. As for stopping it before surgery, 2024 guidance from five medical societies says most patients can keep taking their GLP-1, with a 24-hour liquid diet and other precautions for those at higher risk.
Key takeaways
- BMI cutoffs vary by surgeon. In a 2021 survey of American Association of Hip and Knee Surgeons members, about half required a BMI of 40 and about a quarter used 45.
- For a 5'10" man at 300 pounds (BMI 43.0), getting under 40 means losing about 21 pounds, roughly 7% of body weight.
- The 2024 multi-society guidance says to defer elective surgery during the GLP-1 dose-escalation phase and until GI side effects settle.
- The older 2023 ASA advice (hold a weekly GLP-1 for one week before surgery) has been replaced for most patients by this more individualized approach. Ask your own team which rule they follow.
- Stopping the drug after you qualify carries a real regain risk; plan the post-op period with your prescriber.
Why surgeons use BMI cutoffs
Higher BMI is linked to more complications after joint replacement, especially infection and wound problems. A 2025 review in Orthopedic Clinics of North America collects the numbers. In one national surgical database study of more than 15,000 knee replacements, a BMI of 40 or higher independently predicted 30-day complications (odds ratio 1.47). In a separate cohort of 7,181 patients, periprosthetic joint infection rose from 0.37% at normal BMI to 4.66% in the morbidly obese group, and to 9.8% when morbid obesity was combined with diabetes (Akram et al., Orthop Clin North Am 2025).
The same review reports a 2021 survey of AAHKS surgeons in which 49.9% required a BMI threshold of 40 and 24.5% required 45 before an elective hip or knee replacement. That is why one man hears "under 40" and another hears "under 35" or "under 45." There is no single national number.
The professional society itself has avoided a hard line. An AAHKS workgroup published a literature review on obesity and joint replacement in 2013 to guide surgeon-patient discussions (Springer et al., J Arthroplasty 2013). The 2025 review characterizes the AAHKS position as favoring a holistic, patient-centered approach without strict cutoffs, while noting that BMI 40 to 49 and 50-plus carry disproportionate risk. Its own authors call strict cutoffs "potentially unethical and short sighted" and suggest using BMI to start a risk-modification conversation, with a target of about BMI 40 or a 5% to 10% weight loss.
The flip side matters too. AAHKS highlighted a study finding that patients with obesity gained pain relief and function similar to other patients, concluding that obesity "should not be a deterrent" to joint replacement even though early complications are more likely (AAHKS, 2017).
How much weight you actually need to lose
The CDC defines class 3 (severe) obesity as a BMI of 40 or higher and class 2 as 35 to under 40 (CDC, Adult BMI Categories). Because BMI is weight divided by height squared, the target depends on your height. Here is the math for a man who is 5'10" (70 inches):
| Starting weight (5'10") | Starting BMI | Loss to reach BMI under 40 (278.8 lb) | Loss to reach BMI under 35 (243.9 lb) |
|---|---|---|---|
| 300 lb | 43.0 | 21.2 lb (7.1%) | 56.1 lb (18.7%) |
| 320 lb | 45.9 | 41.2 lb (12.9%) | 76.1 lb (23.8%) |
Calculated from the standard BMI formula (weight in kg divided by height in meters squared); categories per CDC.
A cutoff of 40 is often reachable with single-digit or low double-digit percentage loss. A cutoff of 35 from the mid-40s is a much bigger lift.
What the trials say about the timeline
Two maintenance trials give useful "how fast" data, because everyone took the active drug during an open-label first phase.
- Semaglutide (STEP 4): 902 adults took weekly semaglutide, stepping up to 2.4 mg. They lost an average of 10.6% of body weight in the first 20 weeks (Rubino et al., JAMA 2021).
- Tirzepatide (SURMOUNT-4): 783 adults took tirzepatide at their maximum tolerated dose and lost an average of 20.9% in 36 weeks (Aronne et al., JAMA 2024).
Over a longer stretch, the Zepbound label reports average weight change at 72 weeks of −15.0% on 5 mg, −19.5% on 10 mg and −20.9% on 15 mg, versus −3.1% on placebo (Zepbound prescribing information).
These are averages. Some people lose much more and some much less, and the trials were not run in people waiting for joint surgery, who may move less because of pain. Use them to set a rough expectation, then judge by your own scale weight at follow-up visits.
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The pre-surgery hold: what changed between 2023 and 2024
GLP-1 drugs slow stomach emptying. The Wegovy and Zepbound labels both warn of rare postmarketing reports of pulmonary aspiration during general anesthesia or deep sedation, including in patients who had food in the stomach despite following fasting rules. The Wegovy label adds that available data are insufficient to say whether changing fasting instructions or pausing the drug reduces the risk. Both labels tell prescribers to instruct patients to inform healthcare providers before any planned surgery (Wegovy prescribing information; Zepbound prescribing information).
In June 2023, the American Society of Anesthesiologists advised holding daily GLP-1s on the day of surgery and weekly GLP-1s "a week prior to the procedure/surgery" (ASA, June 2023).
On October 29, 2024, the ASA joined four other groups (the American Gastroenterological Association, American Society for Metabolic and Bariatric Surgery, International Society of Perioperative Care of Patients with Obesity, and Society of American Gastrointestinal and Endoscopic Surgeons) in new guidance. It says "most patients should continue taking" their GLP-1 before elective surgery (ASA, October 2024).
| Issue | ASA 2023 | Multi-society 2024 |
|---|---|---|
| Weekly GLP-1 before surgery | Hold one week before | Most patients continue |
| Higher-risk patients | Not specified | Liquid-only diet for 24 hours before; anesthesia plan adjusted |
| Dose-escalation phase | Not specified | Defer elective surgery until escalation ends and GI side effects resolve |
| Active GI symptoms | Not specified | Wait until symptoms resolve |
| Extra checks | Not specified | Point-of-care ultrasound of stomach contents may be used for highest-risk patients |
Source: ASA 2023; ASA 2024; AGA 2024.
The ASA release lists who counts as higher risk: people in the escalation phase (typically four to eight weeks), people with nausea, vomiting, abdominal pain or constipation, people on higher doses, and people with conditions that slow the stomach, such as Parkinson's disease. The AGA's summary adds that stopping the drug may carry its own risks, and that the stomach-slowing effect lessens over time for most patients (AGA, 2024).
Your hospital's anesthesia department makes the final call, and local protocols can differ from society guidance. Get specific instructions in writing.
After surgery: the regain question
Some men plan to stop the GLP-1 once they qualify. The maintenance trials show what tends to happen. In STEP 4, people switched to placebo after 20 weeks regained 6.9% of body weight over the next 48 weeks, while those who stayed on semaglutide lost another 7.9% (STEP 4). In SURMOUNT-4, people switched to placebo regained 14.0% over 52 weeks, while those who continued lost another 5.5% (SURMOUNT-4).
A new joint lasts longer under less load, and the same weight-related conditions that raised surgical risk do not disappear after the operation. Whether to continue, taper or stop is a conversation for your prescriber and surgeon together. Also watch hydration in recovery: both labels report acute kidney injury, mostly in people dehydrated by nausea, vomiting or diarrhea.
Questions to ask your surgeon and anesthesiologist
Surgeon
- What exact BMI do you require, and is it a hard cutoff or a discussion point?
- Will you recheck my weight at the pre-op visit or on the day of surgery?
- If I reach the target, how soon can we schedule, given that I may still be in dose escalation?
- What do you recommend about continuing the GLP-1 after surgery?
Anesthesiologist or pre-op clinic
- Do you follow the 2024 multi-society guidance or a hold rule?
- Do I need a liquid-only diet the day before?
- If I have nausea or constipation that week, should I call ahead?
- Will you use a stomach ultrasound or change the anesthesia plan?
Where this guide stops
This guide does not tell you whether to hold your GLP-1 or what BMI is right for your surgery. Those depend on your surgeon, your anesthesia team, your other conditions and your hospital's protocol. The weight-loss figures are trial averages, not predictions for you.
Key takeaway: A GLP-1 can make a BMI cutoff reachable, but schedule surgery after dose escalation, follow your team's specific pre-op instructions, and plan for what happens to your weight afterward.
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Frequently asked questions
What BMI do surgeons require for a knee or hip replacement?
It varies. A 2021 survey of AAHKS surgeons found 49.9% required a BMI of 40 and 24.5% required 45, and the society has avoided endorsing a strict cutoff.
How fast can a GLP-1 lower my BMI before surgery?
In trial run-in phases, people lost an average of 10.6% of body weight in 20 weeks on semaglutide (STEP 4) and 20.9% in 36 weeks on tirzepatide (SURMOUNT-4). Individual results vary widely.
Do I have to stop my GLP-1 a week before surgery?
The ASA's 2023 advice was to hold a weekly GLP-1 for a week. The October 2024 multi-society guidance says most patients can continue, with a 24-hour liquid diet and other precautions for higher-risk patients. Follow your own anesthesia team's instructions.
Should I schedule surgery while I'm still increasing my GLP-1 dose?
The 2024 multi-society guidance says elective surgery should be deferred during the dose-escalation phase and until GI side effects resolve, so tell your surgeon where you are in your dosing schedule when booking.
Will I regain weight if I stop the GLP-1 after surgery?
Many people do. In STEP 4, those switched to placebo regained 6.9% over 48 weeks, and in SURMOUNT-4 they regained 14.0% over 52 weeks.
Sources
- Akram F, Tseng J, Behery O, Levine BR. Comorbidities in Total Hip and Knee Arthroplasty Patients: When Is It Okay to Say No? Orthop Clin North Am 2025;56:1-12
- Springer BD et al. (AAHKS workgroup). Obesity and Total Joint Arthroplasty: A Literature Based Review. J Arthroplasty 2013;28(5):714-721
- AAHKS: Study Shows Good Outcomes for Obese TJR Patients (July 2017)
- CDC: Adult BMI Categories
- Rubino D et al. STEP 4 Randomized Clinical Trial. JAMA 2021;325(14):1414-1425
- Aronne LJ et al. SURMOUNT-4 Randomized Clinical Trial. JAMA 2024;331(1):38-48
- Zepbound (tirzepatide) prescribing information, Eli Lilly, revised 08/2026
- Wegovy (semaglutide) prescribing information, Novo Nordisk, revised 06/2026
- ASA: Patients taking popular medications for diabetes and weight loss should stop before elective surgery (June 2023)
- ASA: New Multi-society Clinical Practice Guidance Released (October 2024)
- AGA: Most patients can continue GLP-1 anti-obesity drugs before surgery (2024)
Medical disclaimer: This article is general information, not medical advice, and does not replace a licensed clinician who knows your history. Approvals, labels, coverage and prices change; check the linked sources and talk with your prescriber or pharmacist before making decisions about any medication.