Short answer: NPH insulin has a half-life of about 4.4 hours (apparent; range 1 to 84 hours). Levels peak about 4 hours (range 1 to 12 hours) after a dose. People vary, so treat these as estimates.
NPH insulin (insulin isophane) is human insulin bound to protamine, which makes it a cloudy suspension that is absorbed more slowly: an intermediate-acting insulin. It is sold as Humulin N and Novolin N, and is the 70% part of premixed 70/30 human insulin.
Also known as: Humulin N, Novolin N, isophane insulin, insulin isophane human.
Humulin N is U-100 (100 units/mL) in a 10 mL vial and a 3 mL KwikPen. Novolin N is U-100 in a 10 mL vial and a 3 mL FlexPen. Both are suspensions mixed right before use until evenly cloudy (for Novolin N, a vial is rolled gently 10 times and a FlexPen moved up and down 20 times), then injected right away.
The labels approve NPH insulin to improve blood sugar control in adults and children with diabetes. Label dosing: injected under the skin of the belly, thigh, upper arm or buttocks, rotating sites; the Novolin N label gives it once or twice a day, and in type 1 diabetes it is generally used with a short-acting insulin. The dose is set for each person, with no fixed starting dose. It is never given into a vein or by insulin pump. The Humulin N label says it may be mixed in the syringe with Humulin R or Humalog, drawing those in first. Neither label gives a missed-dose rule.
Neither label has a boxed warning. Low blood sugar is the most common side effect of every insulin, and severe lows can cause seizures or death. The labels also warn: never share a pen, cartridge or syringe, even with a new needle; changes in insulin type, maker, strength or injection site are made under medical supervision with more glucose checks; insulin mix-ups have happened, so the label is checked before each injection; insulin can lower potassium; and heart failure can worsen when insulin is used with a thiazolidinedione such as pioglitazone. The labels give no trial percentages; they list injection site reactions, rare whole-body allergy, swelling, skin pits or thickening, weight gain and insulin antibodies. See side effects of Humulin N and Novolin N, dosing schedules for Humulin N and Novolin N, storage for Humulin N and Novolin N, and Novolin N vs Humulin N and Humulin N vs Lantus. Glossary: intermediate-acting insulin and premixed insulin.
The Humulin N label says that after 0.4 units/kg under the skin in healthy people, insulin peaked at a median of about 4 hours (range 1 to 12) and the strongest effect came at a median of 6.5 hours (range 2.8 to 13). It gives a mean apparent half-life of about 4.4 hours (range 1 to 84 hours), but says a true half-life cannot be estimated accurately because absorption limits the rate. The Novolin N label says the effect begins 1 to 2 hours after a dose and lasts up to 24 hours, depending on dose.
Numbers shown are taken from the source above. Half-life varies from person to person.
How Dose Track handles peptides · Reconstitution calculator · Half-life calculator