Types of insulin
A person can take different types of insulin based on how long they need the effects of the supplementary hormone to last.

Different types of insulin have different effects on blood glucose.
People categorize these types based on several different factors:

speed of onset, or how quickly a person taking insulin can expect the effects to start.
the route of delivery, or whether the insulin requires injection under the skin,into a vein, or into the lungs by inhalation.
concentration
People most often deliver insulin into the subcutaneous tissue, or the fatty tissue located near the surface of the skin.

Three main groups of insulin are available.

Fast-acting insulin
The body absorbs this type into the bloodstream from the subcutaneous tissue extremely quickly.

People use fast-acting insulin to correct hyperglycemia, or high blood sugar, as well as control blood sugar spikes after eating.

This type includes:

Rapid-acting insulin analogs: These take between 5 and 15 minutes to have an effect. However, the size of the dose impacts the duration of the effect. Assuming that rapid-acting insulin analogs last for 4 hours is a safe general rule.
Regular human insulin: The onset of regular human insulin is between 30 minutes and an hour, and its effects on blood sugar last around 8 hours. A larger dose speeds up the onset but also delay the peak effect of regular human insulin.
Intermediate-acting insulin
This type enters the bloodstream at a slower rate but has a longer-lasting effect. It is most effective at managing blood sugar overnight, as well as between meals.

Options for intermediate-acting insulin include:

NPH human insulin: This takes between 1 and 2 hours to onset, and reaches its peak within 4 to 6 hours. It can last over 12 hours in some cases. A very small dose will bring forward the peak effect, and a high dose will increase the time NPH takes to reach its peak and the overall duration of its effect.
Pre-mixed insulin: This is a mixture of NPH with a fast-acting insulin, and its effects are a combination of the intermediate- and rapid-acting insulins.
Long-acting insulin
While long-acting insulin is slow to reach the bloodstream and has a relatively low peak, it has a stabilizing “plateau” effect on blood sugar that can last for most of the day.

It is useful overnight, between meals, and during fasts.

Long-acting insulin analogs are the only available type, and these have an onset of between 1.5 and 2 hours. While different brands have different durations, they range between 12 and 24 hours in total.