How Pharmacies Calculate Your Titration Schedule Supply

Published July 17, 2026 · Medically reviewed content · Updated for 2026

Your compounded semaglutide vial arrives with a label showing a concentration — something like "2 mg/mL" or "5 mg/mL" — and a total volume. But how did the pharmacy decide on that concentration? Why does the same medication come in different strengths at different stages of your treatment? And how do you know when the vial is actually empty versus when there's still usable medication in it?

The answers are in the math — and it's simpler than it looks.

Concentration, Volume, and Dose: The Three Variables

Every compounded vial is defined by three numbers:

• Concentration — how much medication is dissolved in each milliliter of solution (mg/mL)
• Total volume — how much liquid is in the vial (mL)
• Your dose — how much medication you need per injection (mg/week)

From these three numbers, you can calculate exactly how many doses your vial contains and how long it should last:

Doses per vial = (Concentration × Total Volume) ÷ Weekly Dose
Example: A 2.5 mg/mL vial with 3 mL total volume at a 0.5 mg/week dose = (2.5 × 3) ÷ 0.5 = 15 doses = 15 weeks of supply

This is the most important calculation in compounded GLP-1 treatment, and most patients never see it broken down. Once you understand it, you can verify that your prescription makes sense, identify overpayment situations, and plan your refill timing accurately.

How Pharmacies Choose Concentrations

Compounding pharmacies don't make a unique concentration for every patient. They stock a limited set of standard concentrations — typically ranging from 1 mg/mL for early titration doses up to 10 mg/mL or higher for maintenance doses — and your prescriber selects the one that best matches your current dose level.

The goal is to make your injection volume practical. If you're on a 0.25 mg starting dose and the pharmacy uses a 1 mg/mL concentration, you'd draw 0.25 mL per injection — a manageable amount with a standard insulin syringe. If they used a 5 mg/mL concentration for the same dose, you'd draw 0.05 mL — a tiny volume that's harder to measure accurately with a standard syringe.

As you titrate to higher doses, the pharmacy typically moves you to a higher concentration so your injection volume stays in the practical range (usually 0.1 to 0.5 mL per injection). This is why your prescription may change between refills even if the drug and the dose are the same — you're moving to a higher-concentration vial that delivers the same dose in a smaller volume.

Why Titration Complicates the Math

Standard titration for semaglutide looks something like this:

• Weeks 1–4: 0.25 mg/week
• Weeks 5–8: 0.5 mg/week
• Weeks 9–12: 1.0 mg/week
• Weeks 13–16: 1.7 mg/week
• Week 17+: 2.4 mg/week (maintenance)

Each step change means you're drawing a different volume from the vial. A single vial prescribed for 4 weeks at 0.25 mg/week holds a different number of doses than the same vial would at 0.5 mg/week. Pharmacies handle this in several ways:

• Fixed 4-week vials matched to each dose level: You get a new vial at each titration step, each formulated for that dose. This is the cleanest approach but requires precise coordination between your prescriber's titration timeline and the pharmacy's refill schedule.
• Multi-dose vials covering an entire titration phase: Some prescribers write for a vial that covers 8 or 12 weeks, with instructions for increasing the draw volume at specific intervals. This reduces shipments but requires the patient to manage their own dose adjustments by changing how much they draw.
• Concentration changes at mid-titration: Your prescriber may switch you to a higher-concentration vial partway through titration to keep the injection volume practical at higher doses.

Overfill and Dead Space

Compounded vials are intentionally overfilled — typically by 10% to 20% — to ensure patients can draw the full number of prescribed doses even with the small amount of medication that remains in the vial's dead space (the volume that the syringe can't fully extract). This overfill means your vial may contain slightly more medication than the label math suggests.

Some patients use the overfill as a "bonus" dose. Whether this is appropriate depends on your prescriber's instructions and the pharmacy's beyond-use dating. An extra dose is only useful if the vial is still within its expiration window and has been properly stored.

When the Math Doesn't Match

If you run out of medication before your next refill is scheduled, or if you seem to have far more left than expected, something in the math is off. Common causes:

• Incorrect draw volume: You may be drawing more or less than prescribed. Use a syringe with markings appropriate for your draw volume — a 1 mL syringe for volumes under 0.5 mL, a 3 mL syringe for larger draws. The smaller the syringe, the more precise the measurement.
• Dose change not reflected in supply: Your prescriber increased your dose but the pharmacy didn't adjust the supply duration — you're using more medication per week than the refill schedule assumes.
• Vial wasn't full: While rare, manufacturing inconsistencies can result in a vial with less than the labeled volume. If you suspect short-fill, contact the pharmacy with the lot number.

A Simple Tracking Method

Keep a log — on paper or in your phone — recording:

• The date of each injection
• The dose drawn (in mg and in mL)
• An estimate of remaining volume in the vial (many patients hold the vial up to light and mark approximate levels)

This 10-second habit gives you the data to predict when you'll need a refill, verify that the vial's supply matches the label, and catch discrepancies before you run out.

Frequently Asked Questions