Understanding Your Dose (mg vs mL vs Units)

When you receive your medication and instructions, you'll see terms like mg, mL, and units. These are not interchangeable—and confusing them can lead to an incorrect dose. This guide explains what each term means and how to use your instructions correctly.

The Three Terms Explained

mg — Milligrams (the Amount of Medication)

mg measures the actual amount of active medication you're taking. This is your dose. For example, your prescription might say you take 2.5 mg of tirzepatide or 0.25 mg of semaglutide per week.

Your provider prescribes your dose in mg. This number reflects the clinical decision about how much medication your body should receive.

mL — Milliliters (the Volume of Liquid)

mL measures the volume of liquid you draw into a syringe. This is not the same as your dose in mg.

How many mL you inject depends on the concentration of your medication (see below).

Units — The Measurement on Your Syringe

Units are the markings on your syringe. Insulin-style syringes (commonly used for these medications) are marked in units, with 100 units equaling 1 mL.

When your instructions say "inject 20 units," that means draw the plunger back to the 20-unit mark on your syringe.

How Concentration Connects Them

The relationship between mg and mL is determined by the concentration of your medication, which is expressed as mg/mL (milligrams per milliliter).

Here's how it works:

• If your medication is 2 mg/mL and your dose is 2 mg, you inject 1 mL (or 100 units)

• If your medication is 4 mg/mL and your dose is 2 mg, you inject 0.5 mL (or 50 units)

Same dose (2 mg), different volume. This is why it's essential to follow your specific prescription instructions rather than assuming the same units you used before will apply.

Why Your Units May Differ From Someone Else's

Two people on the same dose (in mg) from different pharmacies may inject a completely different number of units. This is because:

• Compounded medications can be prepared at different concentrations (mg/mL)

• Different pharmacies use different formulations

• Even the same pharmacy may use different concentrations between batches

This is normal. It does not mean one medication is stronger or weaker—it means the liquid is more or less concentrated. The amount of active medication you receive is determined by the mg dose your provider prescribed, not by how many units you inject.

How to Read Your Medication Label

Your label will typically include:

• The medication name — e.g., Semaglutide, Tirzepatide

• The total amount — e.g., 5 mg/1.25 mL (total volume in vial)

• The concentration — e.g., 4 mg/mL

• Your dose — e.g., Inject 0.5 mL or 50 units weekly

Your instructions may list your dose in mL, units, or both. Follow whatever format is listed—they are telling you the same thing expressed different ways.

A Practical Example

Let's say your prescription says: "Inject 0.5 mg weekly."

• Your vial label says: 2 mg/mL

• 0.5 mg ÷ 2 mg/mL = 0.25 mL

• 0.25 mL = 25 units on an insulin syringe

If your next refill comes from a pharmacy using a 4 mg/mL concentration, the same 0.5 mg dose would now be:

• 0.5 mg ÷ 4 mg/mL = 0.125 mL = 12.5 units

Always check your instructions with each refill. The units may change even if your mg dose stays the same.

The Most Important Rule

Always follow the instructions included with your current order.

Do not use instructions from:

• A previous refill

• Another person's prescription

• Online guides that reference different formulations

Your instructions are specific to your current medication's concentration and your prescribed dose. They are the only instructions you should follow.

If Your Instructions Seem Wrong

If something looks off about your instructions—the units seem much higher or lower than before, or you're unsure how to read the label—contact your provider or support before injecting.

You can reach the team through your patient portal or by emailing [email protected].

Summary

• mg = the amount of active medication (your dose)

• mL = the volume of liquid you inject

• Units = the measurement on your syringe (100 units = 1 mL)

• Concentration (mg/mL) links your dose to the volume you inject

• Different pharmacies may use different concentrations — your units may change between refills

• Always follow your current instructions, not previous ones