Every insulin product is classified by its onset (how soon it starts lowering blood sugar), peak (when it works hardest), and duration (how long it lasts). Doctors often combine types to cover both meals and the background, all-day need for insulin.
| Category | Onset | Peak | Duration | Typical use |
|---|---|---|---|---|
| Rapid-acting | 10-20 min | 1-2 hrs | 3-5 hrs | Taken with meals |
| Short-acting (regular) | 30 min | 2-4 hrs | 5-8 hrs | Taken before meals |
| Intermediate-acting (NPH) | 1-2 hrs | 4-12 hrs | 12-18 hrs | Background coverage |
| Long-acting | 1-2 hrs | minimal peak | up to 24+ hrs | Once/twice-daily background |
| Ultra-long-acting | 6 hrs | none | 36+ hrs | Background coverage |
| Premixed | varies | varies | varies | Combines two types in one pen |
Rapid- and short-acting
These cover the glucose spike from a meal. Rapid-acting analogs are usually taken right before or with food; regular (short-acting) insulin is typically dosed a little earlier since it takes longer to kick in.
Intermediate- and long-acting
These provide a steady background level of insulin between meals and overnight, mimicking the small, constant trickle a healthy pancreas releases even when you're not eating.
Premixed insulin
Some people use a premixed pen that combines a rapid or short-acting insulin with an intermediate one in a fixed ratio, reducing the number of injections needed per day.