Dose vs. concentration: why your vial says a bigger number

Two different numbers describe your medication, and they don't mean the same thing:

• Dose is how much medication you take each week — for example, 10 mg once a week. This is set by your provider, and it's what actually changes when you "increase your dose."
• Concentration is how strong the liquid in the vial is — for example, 20 mg/mL means there are 20 milligrams of medication in every milliliter of liquid.

A higher concentration is not a higher dose

As patients move to higher weekly doses, Belle sometimes ships a more concentrated vial (for example, 20 mg/mL instead of 10 mg/mL) so the amount you inject stays a comfortable, small volume. The number of units you draw is calculated from both your dose and the vial's concentration — which is exactly why a unit count on its own doesn't tell you your dose.

Same dose, different vial: how your units change

If your new vial is stronger, you draw fewer units. If it is weaker, you draw more. Your weekly dose in milligrams stays the same.

On a standard 100-unit syringe, 100 units is 1 mL, so each unit is 0.01 mL. Each unit holds the vial's concentration divided by 100 in milligrams. Here is how the same dose looks in different vials (the math is mg ÷ mg/mL × 100 = units):

When the concentration doubles, the units you draw are cut in half. Nothing about your dose changed. Only the strength of the liquid did.

It works the other way too. A weaker vial needs more units. For example, about 17 units from a 30 mg/mL vial is 5 mg. Those same 17 units from a 10 mg/mL vial are only 1.7 mg. To stay at 5 mg with the weaker vial you would draw 50 units. This is why you should never carry your old unit count over to a new vial.

The same number of units can also be two different doses. 75 units from a 10 mg/mL vial is 7.5 mg. 75 units from a 20 mg/mL vial is 15 mg. A unit count is not a dose, and it is not a limit either. The only way to know what 75 units means is to know the concentration printed on that vial.

One more case: if your concentration stayed the same but your unit count went up, you are drawing more medication. That should only happen when your prescription says so. If you did not expect it, message your care team before your next injection.

Getting a vial with a different strength never changes your dose. Your dose only changes when your provider approves it.

"Can I jump to 20 mg?"

A 20 mg/mL vial does not mean you're on 20 mg. Your weekly dose only changes when your provider approves a dose increase — the concentration printed on the vial doesn't change it. If you'd like to increase your dose, we can start that review with your provider.

Moving from another provider, pharmacy, or medication

Unit counts do not travel from one vial to another. If you used a different provider, a med spa, or a different pharmacy before, the number of units you drew then only made sense for that vial. For example, 70 units from a 12.5 mg/mL vial is 8.75 mg. The same 70 units from a 10 mg/mL vial is 7 mg.

Tell your care team the concentration (mg/mL) and the number of units you drew before. They can work out what that was in milligrams and what your Belle prescription should be. Your dose here is set by your provider, not by matching an old unit count.

Semaglutide and tirzepatide cannot be converted into each other. They are different medications with different dosing scales, so a number of units (or milligrams) of one does not equal any amount of the other. Your provider chooses the starting dose if you switch. We also cannot tell you in advance whether the injection volume will be bigger or smaller, because the concentration depends on the vial the pharmacy sends.

Will my vial concentration change? Can I ask for one?

The pharmacy decides the concentration, not Belle and not you. It depends on what the pharmacy has available, your dose, and how long a supply is being filled (longer plans can come with a more concentrated vial). Because of that:

• Your concentration can be different from one shipment to the next, and from one pharmacy to another. We cannot know in advance what you will get.
• When your dose goes up, the vial may or may not change strength. Either way, your updated unit count is written on your prescription.
• Belle cannot pick or promise a specific concentration, or a specific number of units.

Always check the mg/mL on the label of each new vial before your first injection, and compare it to your written instructions.

If a vial's volume is hard for you to measure, or the unit count feels too large, tell your care team. They can look at options, which may include which pharmacy partner fills your order. We cannot guarantee an exact unit count. Going back to a dose you took before is your provider's decision. See "How to request a dose change."

Fewer units does not mean less medication

A stronger vial holds the same medicine in less liquid. If you went from 100 units to 50 units for the same 2.5 mg dose, you are getting the same dose. The vial is just more concentrated.

How many doses a vial gives you depends on the total milligrams in the vial divided by your weekly dose in milligrams. It does not depend on the number of units.

Two vials in one order can be different. Different dose steps sometimes ship in different concentrations. Use only the instructions and the concentration for the vial you are using right now. If two vials have the same concentration but different total volume, you do not need to change anything: the vial with more liquid simply holds more doses.

Not sure your draw is right? Check in this order

1. Find the concentration on the vial in your hand. It is printed in mg/mL on the label. (If the label shows total milligrams and total volume instead, divide the milligrams by the milliliters.)
2. Find your dose and units in your written instructions. They are in your patient portal and on your prescription.
3. Check that they match. Units × mg/mL ÷ 100 should equal your dose in milligrams. Belle's dosage calculator will do this for you, or see "How do I use Belle's dosage calculator?"
4. If they match, draw the units as written. If they do not match, or you are unsure, do not guess. Send your care team a photo of the vial label and your instructions before your next injection. If your portal and label show different numbers, see "How to find your dose and how many units to inject."

Why we ask how many units you draw: your prescription is written in milligrams, but the same units mean different milligrams in different vials. Asking for your units lets us confirm you are actually injecting the dose that was prescribed.

If you find you have been drawing a different amount than your instructions say, too low or too high, tell your care team. They will confirm next steps with your provider. Please do not change your dose on your own to make up the difference.