Starting a GLP-1 When You’re Already on Insulin: A Patient-Friendly Guide

If you’re already using insulin and your clinician has recommended adding a GLP-1 medication—such as Ozempic® (semaglutide), Mounjaro®/Zepbound® (tirzepatide), or Rybelsus® (oral semaglutide)—you’re not alone. Combining a GLP-1 with insulin can improve blood sugar, help with weight, and often simplify your day-to-day diabetes routine. This guide explains how the combo works, what to expect in the first few weeks, how to reduce the risk of lows, and ways to lower your out-of-pocket costs.

Why add a GLP-1 when you’re already on insulin?

GLP-1 medicines help your body release insulin only when glucose is high, slow stomach emptying (which blunts after-meal spikes), and reduce appetite. For many patients that means:

Lower A1C with fewer hypoglycemia episodes than simply increasing insulin
Less mealtime insulin over time—and sometimes a lower total daily insulin dose
Support for weight loss or preventing further weight gain from insulin alone

Tirzepatide (Mounjaro/Zepbound) also activates the GIP pathway, which can provide additional glucose and weight benefits in some people.

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Step 1: Know your starting point

Before you add a GLP-1, capture a clear snapshot of your current control:

Recent A1C, kidney function (eGFR), and liver tests if ordered
A week of CGM data or meter readings (fasting, pre-meal, 2-hour post-meal, bedtime)
Your current basal dose (e.g., Tresiba, Lantus/Toujeo) and mealtime insulin (units and timing)
Any hypoglycemia you’ve had recently, especially overnight or after exercise

This baseline helps your provider choose the right GLP-1 and plan safe insulin adjustments.

Step 2: Start low, go slow (GLP-1 titration)

Most GLP-1s begin at a low dose to minimize nausea, then increase every 2–4 weeks as tolerated. General tips:

Take the first dose on a calm day so you can monitor how you feel
Eat smaller, slower meals; favor lean protein, veggies, and fiber
Sip fluids through the day; avoid heavy, greasy meals at first
If nausea hits, bland foods (crackers, broth, ginger tea) can help

Tell your provider if nausea is persistent—dose pacing can be adjusted.

Step 3: Adjusting insulin—common starting strategies

Your team will personalize this, but typical approaches include:

If you use basal insulin only (no mealtime insulin):

Many clinicians keep basal the same initially if A1C is above target and lows are rare
If you’re near goal or prone to lows, your provider may reduce basal 10–20% on GLP-1 start and reassess with CGM data over 3–7 days

If you use basal + mealtime (bolus) insulin:

A common move is to reduce mealtime insulin by 10–20% at the first GLP-1 dose, especially for larger carb meals
Some patients skip or halve the bolus for smaller, low-carb meals while watching post-meal readings
Basal may stay the same at first; if fasting lows occur, a 10–20% basal reduction is often enough

Important: Any insulin cuts should be guided by your clinician and data-driven with CGM or careful meter checks.

Step 4: Use your CGM (or meter) like a coach

The safest way to find your new balance is to watch patterns, not single numbers:

Review time-in-range and overnight trends daily in week 1–2
Set hypo alerts a bit higher for the first week (e.g., 80–85 mg/dL)
Note meals that still spike you; your bolus reduction may be too generous for those
After 3–4 days on a stable dose, your provider may suggest small tweaks

Aim for small, steady changes; avoid multiple adjustments at once.

Step 5: Prevent and treat lows

Adding a GLP-1 often lowers the insulin you need, which is good—but unexpected lows can still happen as your appetite and intake change.

Carry fast carbs (glucose tabs/gel) at all times
If you feel shaky, sweaty, foggy, or very hungry—check and treat
Recheck in 15 minutes; if still below target, treat again
Update your care team if you have repeated lows, so doses can be adjusted

Special situations

Illness (sick-day rules): Hydrate, monitor more often, and follow your clinic’s plan for ketone checks and correction dosing. If you’re vomiting or can’t keep fluids down, seek care.
Procedures/surgery: GLP-1s delay stomach emptying. Your team may advise holding weekly GLP-1s before anesthesia and using a simple basal/bolus bridge. Get specific instructions in advance.
Exercise days: You may need less mealtime insulin and a plan for pre-/post-workout carbs while on a GLP-1, especially as weight and insulin sensitivity improve.
Pregnancy planning: GLP-1s are typically stopped before conception; insulin remains the safety standard. Discuss timelines with your provider.

Affording your GLP-1 + insulin combo

GLP-1s and modern basals can be pricey in the U.S., especially with deductibles or coverage denials. Many Americans lower costs by using a Canadian prescription referral service (such as Over the Border Meds) that sources from licensed Canadian pharmacies:

Cash prices are often significantly lower than U.S. retail
No U.S. insurance hurdles; order up to a 90-day personal-use supply
Pharmacist support for pens, needles, and storage (cold-chain shipping for GLP-1s/insulin)

If cost keeps you from starting or staying on therapy, ask your clinician about Canadian options so you can follow the plan consistently.

The bottom line

Adding a GLP-1 to insulin can smooth your glucose, cut mealtime insulin, and support weight loss—but it works best with a clear plan:

Start low and pace the titration
Make modest insulin reductions (especially bolus) with close CGM/meter checks
Carry fast carbs and adjust quickly if lows appear
Keep your care team in the loop, especially during illness, exercise changes, or procedures
If affordability is a barrier, explore ordering from Canada so you never miss a dose

With the right setup and support, the GLP-1 + insulin combination can help you feel better, simplify your routine, and reach your glucose goals safely.