Short answer: It depends on the product. The Humalog label says within 15 minutes before a meal or right after it, the NovoLog label says within 5 to 10 minutes before a meal, and the Humulin R U-500 label says about 30 minutes before meals. Symlin, used alongside mealtime insulin, goes in right before each major meal. Your prescriber sets the plan for your own insulin.
| Product | Timing in the label | Section |
|---|---|---|
| Humalog (insulin lispro) U-100 and U-200 | Within 15 minutes before a meal or immediately after a meal | 2.2 |
| NovoLog (insulin aspart) | Within 5 to 10 minutes before a meal | 2.2 |
| Humulin R U-500 (concentrated regular insulin) | Usually two or three times a day, about 30 minutes before meals | 2.2 |
| Symlin (pramlintide), with mealtime insulin | Immediately before each major meal (at least 250 kcal or 30 g carbohydrate) | 2.4 |
All four are injected under the skin. The Humalog and NovoLog labels list the abdomen, thigh, upper arm and buttocks as sites; the Symlin label says abdomen or thigh, not the arm.
Timing follows how fast each product starts working. Section 12.2 of the Humalog label says it has a faster onset and shorter duration than regular human insulin, with one unit lowering glucose as much as one unit of regular insulin. The NovoLog label says its maximum glucose-lowering effect came 1 to 3 hours after injection, with a duration of 3 to 5 hours, in a study of 22 people with type 1 diabetes.
Humulin R U-500 behaves differently because of its strength. Its label describes an onset under 15 minutes and a mean duration of 21 hours (range 13 to 24) in its study, acting as both mealtime and background insulin, and warns that severe low blood sugar may develop as long as 18 to 24 hours after an injection.
Both the Humalog and NovoLog labels say the times for onset, peak and duration are general guidelines only: absorption varies between people and within the same person, and is affected by the injection site, exercise and other factors.
Of these products, only the Humalog label offers an after-meal option in its dosing section, as "immediately after a meal." The NovoLog dosing section gives a before-meal window only. None of these labels gives a rule for a dose that was missed or taken late; the Humalog and NovoLog labels ask prescribers to teach patients how to handle a skipped insulin dose.
The labels warn that accidental mix-ups between insulin products happen and say to check the insulin label before each injection. They also say changes in insulin product, strength, injection site or method can affect blood sugar control, and should be made under medical supervision with more frequent glucose checks.
A log that records the product, the dose in units and the time of each injection makes timing and mix-ups easier to review with your diabetes team. Dose Track lets you log each mealtime dose with its time and site, and remind you before meals on the schedule your prescriber gives you.
Read more on Dose Track: Missed a dose of Humalog · Missed a dose of NovoLog · Humulin R U-500 side effects · Concentrated insulin (glossary) · Insulin pen (glossary) · How to store Humalog