Look at the dotted line (Kinetic) at the lower left of this graph, and then at the solid one (Dynamic) also at lower left. The beginning of the dotted kinetic line is where the insulin is injected into the body; the beginning of the solid dynamic one is where the insulin is present in the bloodstream in enough quantity where it begins lowering blood glucose. The point where it actually starts working is the onset. Onset varies according to the type, origin and strength of an insulin.

Onset occurs when the insulin reaches the bloodstream and begins lowering blood glucose. Insulins with long onset (2 to 4 hours) are typically the long-acting insulins, or those that have long duration. Those insulins with the shortest onset times (30 minutes) belong to the fast-acting category, or those with relatively short duration. The intermediate-acting insulins have a 1-2 hour onset with 8-12 hours of duration. [1]

Among the fast-acting insulins, those based on human insulin, also called Analog insulins, such as Humalog, Novolog/NovoRapid and Apidra, have the fastest onsets. In general, any insulin that has no type of suspension will have a quick onset.

Analog mixed insulins are suspended by the use of protamine to create special insulin crystals. These mixes also begin with the basic insulins: Humalog or Novolog/NovoRapid.

The long-acting analog insulins Lantus and Levemir don't have the "traditional" types of suspension but they are prolonged by other means. Lantus doesn't form crystals until it's under the skin; the crystals are slow to absorb. Levemir uses a binding to albumin in the bloodstream to prolong its action.

Working with Onset

A predictable onset is a necessary part of working with overlap. Insulins with short onset frequently peak in less than 4 hours after injection. Food can be given to extend onset and peak response.

See also peak, duration, and carryover. I16


  1. Bruyette, David. Blood glucose curve: interpretation. VetSteam Canis.

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