The insulin that has the longest duration of action, which is the length of time it works, is usually either the intermediate-acting insulins such as NPH insulin (human), or the long-acting insulins such as insulin glargine (Lantus) or insulin determir (Levemir). Their duration of action can be up to 24 hours long.

Intermediate insulin is often combined with rapid or short acting insulins and is usually dosed twice a day. Intermediate insulins cover blood glucose elevations when rapid-acting insulins stop working.

Long-acting insulins lower blood glucose levels when rapid-acting insulins stop working and are used once or twice a day. Insulin glargine (Lantus) is used once a day and is always given at the same time, regardless of meals. Insulin detemir (Levemir) is used once or twice a day, also without regards to meals.