NPH insulins are intermediate-acting human insulins. In Finland, they are for sale under the brand names of Protaphane and Humulin NPH. NPH is an abbreviation of Neutral Protamine Hagedorn.
NPH insulin has an onset of action of 1–2 hours, peak effect in 4–10 hours and duration of action for adults of 12–18 hours. In NPH insulin, the dose size has an effect on the duration of action; smaller doses have a shorter duration of action, while bigger doses have a longer duration of action.
NPH insulins are opaque insulin suspensions. They must be carefully mixed prior to injection in order to ensure an even insulin content. The amount of NPH insulin entering the circulation varies a lot from one individual to the next or, in the case of the same person, depending on the day. One reason is that the product is not always mixed thoroughly enough to evenly distribute the insulin crystals to suspension and ensure that the targeted amount of insulin is always injected.
The use of NPH insulin has become significantly less common, with newer and longer-acting insulin derivatives that absorb more evenly entering the market. To some degree, they are used to treat both type 2 diabetes and gestational diabetes in children. They are not recommended as a basal insulin product for type 1 diabetes.
NPH insulin may be used as a morning injection for person who uses cortisone tablets to treat other conditions.