What medications interact with GLP-1s?

The interaction list is short by blockbuster-drug standards, but the entries are consequential: Mechanism 1 — additive glucose-lowering (the dangerous one): - Insulin and sulfonylureas (glipizide, glyburide, glimepiride): GLP-1s alone rarely cause lows, but stacked on unconditional insulin-pushers they do. Standard practice is pre-emptive reduction — roughly 20% on insulin, halving or pausing sulfonylureas — coordinated by the prescriber before the first dose, with glucose monitoring through titration. Know the hypo symptoms cold. Mechanism 2 — slowed gastric emptying changes oral-drug absorption (worst during dose escalations, settling at steady state): - Oral contraceptives: the headline entry. Tirzepatide’s label specifically advises backup (non-oral) contraception for 4 weeks after starting and after each dose increase — reduced pill absorption plus weight-loss-restored fertility is the “Ozempic baby” recipe. - Levothyroxine: absorption timing matters anyway (empty stomach); on a GLP-1, recheck TSH a couple of months after starting and adjust as needed. - Warfarin and narrow-therapeutic-index drugs (some anti-seizure medications, transplant immunosuppressants, digoxin, lithium): not contraindicated — monitored. Expect an extra INR or level check during titration. - Time-critical or absorption-sensitive medications generally (e.g., some Parkinson’s regimens): worth one pharmacist conversation about timing. Adjacent cautions that aren’t classic interactions: other appetite suppressants or weight drugs stack GI misery without proven added benefit; alcohol’s three frictions; diuretics amplifying dehydration on blunted thirst; and ondansetron — commonly co-prescribed for nausea — carrying its own QT-prolongation list worth flagging if you’re on antiarrhythmics or certain antidepressants/antibiotics. The cheap, high-yield move: one full medication-list review with a pharmacist or your prescriber at the start — it covers everything above in ten minutes, free at most pharmacies, and is precisely the screen a legitimate program’s intake should be performing anyway.