GLP-1 receptor agonists lower blood sugar mainly by amplifying the body’s own insulin response and suppressing glucagon — both glucose-dependent mechanisms that carry low intrinsic hypoglycemia risk. The risk rises sharply when a GLP-1 is layered on top of EXOGENOUS insulin or a sulfonylurea, which push insulin regardless of glucose. The FDA labels for Ozempic, Wegovy, Mounjaro, and Zepbound and the American Diabetes Association Standards of Care both recommend proactive dose reductions of those co-medications at GLP-1 start.
Co-medication adjustment table
| Co-medication class | Examples | Recommended adjustment at GLP-1 start |
|---|---|---|
| Basal (long-acting) insulin | Lantus, Tresiba, Toujeo, Levemir, Basaglar | Reduce dose by 20–25% at GLP-1 start. Further reduction if A1C is already at goal or fasting glucose trends below 100 mg/dL. |
| Prandial (mealtime) insulin | Humalog, NovoLog, Apidra, Lyumjev, Fiasp, Admelog | Reduce by 25–50% if appetite drop is expected to shrink meal size. Many patients can pause prandial insulin entirely after the GLP-1 reaches a therapeutic dose — coordinate with the prescriber. |
| Sulfonylureas | Glipizide, glimepiride, glyburide | Consider full discontinuation, or reduce by 50% if continued. The ADA Standards of Care flag sulfonylureas as the highest-hypoglycemia oral class and recommend deprescribing when a GLP-1 is added. |
| Meglitinides | Repaglinide, nateglinide | Reduce by 50% or discontinue. Same insulin-secretagogue hypoglycemia profile as sulfonylureas. |
| Metformin | Glucophage, Glumetza, Fortamet, Riomet | No adjustment. Continue full dose. Very low intrinsic hypoglycemia risk and ADA-preferred combination partner with GLP-1s. |
| SGLT2 inhibitors | Jardiance, Farxiga, Invokana, Steglatro | No adjustment. Additive cardiorenal benefit with no shared hypoglycemia mechanism; the ADA endorses GLP-1 + SGLT2 combination for high-risk type 2 diabetes. |
| DPP-4 inhibitors | Januvia, Tradjenta, Onglyza, Nesina | Discontinue. The FDA labels for Ozempic, Mounjaro, Wegovy, and Zepbound state these products have not been studied with other GLP-1 receptor agonists, and DPP-4 inhibitors act on the same incretin pathway with no additive efficacy when a GLP-1 is on board. |
| Pioglitazone | Actos | No adjustment. Watch for weight regain or fluid retention masking GLP-1 weight-loss progress. |
| Other GLP-1 RAs | Victoza, Saxenda, Trulicity, Bydureon, Byetta, Adlyxin | Discontinue one before starting another. The FDA labels say GLP-1 receptor agonists have not been studied in combination with another GLP-1 RA. |
Hypoglycemia warning signs
- Shakiness or trembling hands. Often the earliest cue.
- Cold sweat or clammy skin, especially with no other reason to be sweating.
- Confusion, trouble concentrating, or slurred speech. Treat immediately and reassess.
- Dizziness, lightheadedness, or feeling faint.
- Racing or pounding heartbeat.
- Blurred vision, irritability, sudden hunger, or headache.
Treat with 15–20 grams of fast-acting carbohydrate — 4 oz juice, 4 glucose tablets, 1 tablespoon honey, or 5–6 hard candies. Recheck blood glucose in 15 minutes and repeat if still below 70 mg/dL. This is the ADA-endorsed “15-15 rule.”
A1C monitoring after GLP-1 start
The ADA Standards of Care call for A1C every 3 months until at goal, then every 6 months. After adding a GLP-1, most prescribers recheck at 4–8 weeks with a fasting glucose or continuous-glucose-monitor (CGM) snapshot to catch over-correction early, then a formal A1C at the 3-month mark. If insulin or sulfonylurea was reduced at start, the 3-month A1C tells you whether the reduction held, needs to go further, or can be partially restored.
Red flags — call your prescriber
- Severe hypoglycemia. Loss of consciousness, seizure, or needing someone else to give juice, glucagon, or call 911. Any single episode is a same-day call.
- Three or more mild hypoglycemia episodes per week, even if you self-treat. The co-medication dose is too high.
- A1C trending below 6.0% on a regimen that still includes insulin or sulfonylurea. Risk of unrecognized hypoglycemia rises.
- Fasting glucose consistently below 80 mg/dL for more than a week. Time to step the basal insulin down again.
- Hypoglycemia unawareness — glucose readings under 60 mg/dL without any symptoms. A regimen reset is overdue.
What this cheat sheet does not cover
This page is the diabetes co-medication framework only. It does not cover non-diabetes interactions (oral contraceptive efficacy on tirzepatide, levothyroxine timing around delayed gastric emptying, warfarin INR monitoring), pediatric type 2 diabetes protocols, gestational diabetes, type 1 diabetes management, or DKA-risk planning. Sick-day rules and surgery holds live on the GLP-1 Sick-Day Guide. Talk to the prescriber managing your diabetes before changing any insulin or oral agent dose.