Comprehensive interactions reference for GLP-1 receptor agonists.
Insulin and sulfonylureas
Hypoglycemia risk when combined. Adjust insulin or sulfonylurea downward when initiating GLP-1. Continuous glucose monitoring helpful.
Anesthesia / surgery
Delayed gastric emptying raises aspiration risk during anesthesia. ASA 2023 guidance: hold weekly GLP-1 ≥1 week before elective procedures with anesthesia. Hold daily ≥1 day. Coordinate with anesthesia team.
Oral contraceptives (tirzepatide-specific)
Tirzepatide label recommends backup contraception for 4 weeks at initiation and after each dose escalation due to potential impact on OCP absorption. Critical for women of reproductive age.
Pregnancy planning
Stop sema ≥2 months and tirz ≥1 month before planned conception. GLP-1 may restore ovulation in patients with weight-related anovulation (PCOS) — unexpected pregnancy is well documented.
Levothyroxine
Delayed gastric emptying can affect levothyroxine absorption. Take levothyroxine consistently with respect to timing; monitor TSH after starting GLP-1.
NSAIDs
Combined nephrotoxicity risk in dehydrated patients (vomiting from GLP-1 + NSAID nephrotoxicity). Avoid combination during active GI side effects.
Warfarin
Limited data. Monitor INR more closely during titration.
Slow-absorbed orals broadly
Delayed gastric emptying may shift the absorption curve for many oral medications. Most clinically insignificant; some narrow-therapeutic-index drugs (digoxin, lithium, theophylline) warrant attention.