All insulin types are broadly divided into two roles: bolus (prandial) insulin — given before meals to offset the rise in glucose after eating — and basal insulin, which maintains a background insulin level between meals and overnight. In practice, a treatment plan usually combines several types, tailored individually by a doctor.

Rapid-Acting Insulin (Ultra-Short)

Starts working the fastest — roughly 5–15 minutes after injection, peaking around 1–2 hours later and lasting a total of about 3–4 hours. It's described in the medical literature as a bolus dose given right before a meal (15–30 minutes ahead, or with the first bite) to offset the expected glucose spike. Examples include insulin aspart, lispro, and glulisine (listed as international nonproprietary names, for reference).

Short-Acting Insulin ("Regular")

Starts working more slowly than the ultra-short type — around 30 minutes after injection — peaking at 2–4 hours and lasting 5–8 hours. Because of its slower onset, it's usually given about 30 minutes before a meal. It's one of the oldest insulin types, known as "Regular" insulin.

Intermediate-Acting Insulin (NPH)

The most common example is NPH insulin (Neutral Protamine Hagedorn). It starts working in 1–3 hours, peaks at 4–6 hours after injection, and lasts 16–24 hours. Sources note that an evening dose of NPH can "cover" its peak right around the morning — linked to the natural tendency of glucose to rise before waking, known as the "dawn phenomenon."

Long-Acting Insulin — Basal ("Overnight")

Designed to provide steady, largely peakless background coverage over 24 hours. It starts working in 1–2 hours and lasts about 24 hours. Examples include insulin glargine and insulin detemir. Because it's most often injected once a day, it's commonly called "overnight" insulin in everyday conversation — though it formally provides a basal level around the clock, not just at night. An estimated roughly half of a person's daily insulin need is met by basal insulin.

A separate subgroup is ultra-long-acting insulin — for example, glargine U300 and degludec: these last more than 24 hours (degludec, by some accounts, up to about 42 hours), giving more flexibility in injection timing. Once-weekly insulins are also in development.

Mixed (Combined) Insulins

These are premixed combinations with a fixed ratio of two insulin types — for example, a 70/30 mix (70% intermediate-acting, 30% rapid- or short-acting). Such a product provides both basal and bolus coverage in a single injection, reducing the number of daily shots, though it offers less flexibility in adjusting each component's dose separately.

Modern Insulins

Beyond the classic analogs described above, insulin pharmacology keeps evolving. A few directions that have emerged or gained traction in recent years:

  • Biosimilars — insulins that are structurally and therapeutically equivalent to the original product, entering the market once the originator's patent protection expires. They don't differ in effectiveness or safety, but they increase competition and make insulin therapy more affordable.
  • Concentrated insulins (U-200, U-300, U-500) — contain 2–5 times more units per mL than the standard U-100. This allows a high dose to be delivered in a smaller volume of liquid — convenient for people with significant insulin resistance.
  • Insulin icodec — the first basal insulin designed for once-weekly injection instead of daily dosing. It binds tightly but reversibly to blood albumin, forming a kind of "depot" that releases insulin evenly over the week. It is currently used in adults with type 2 diabetes.
  • "Smart" insulin pens — record the time and size of each dose and send that data to a smartphone app. This helps avoid missed injections and lets people share their dosing log with a doctor during a visit.
  • Inhaled insulin — an ultra-rapid-acting insulin form that's inhaled before meals instead of injected as bolus insulin. Its use is limited and it has contraindications, including in chronic lung disease.

Insulin Pen Needles

Pen needles are chosen based on two parameters — length (typically 4–12 mm) and thickness, measured in gauge: the higher the number, the thinner the needle. The most common needles today are 29–34G.

  • Shorter, thinner needles (4–5 mm) are considered adequate for most adults regardless of body weight by current clinical guidelines — they deliver insulin under the skin just as effectively while lowering the risk of accidentally injecting into muscle.
  • With a short needle, the skin is usually not pinched and the needle is inserted at a 90° angle; a doctor may recommend a different technique for children and people with very low body weight.
  • Pen needles are intended for single use — manufacturers and doctors recommend replacing the needle before every injection, since reuse dulls the tip (making injections more painful) and raises the risk of microtrauma or infection.
  • There are safety pen needles with a mechanism that shields the tip immediately after injection — reducing the risk of an accidental needlestick for the person injecting or whoever is assisting.
  • Injection sites should be rotated (abdomen, thigh, arm, buttock) — this prevents lipodystrophy (lumps under the skin), which over time impairs insulin absorption.
This article describes insulin categories in general, informational terms — it does not recommend a specific product or dosage. The type, regimen, dose of insulin, and needle length should be determined individually by a doctor for each patient.

Comparison Table

Insulin Type Onset Peak Duration
Rapid-acting (ultra-short) 5–15 min 1–2 hr 3–4 hr
Short-acting (Regular) ~30 min 2–4 hr 5–8 hr
Intermediate-acting (NPH) 1–3 hr 4–6 hr 16–24 hr
Long-acting / basal 1–2 hr largely peakless ~24 hr
Ultra-long-acting 30–90 min largely peakless >24 hr (up to ~42 hr)
Mixed (combined) depends on composition two peaks 16–24 hr

These figures are approximate ranges commonly cited in the medical literature — the actual action profile can vary by specific product, dose, injection site, and individual factors. Insulin doses are often adjusted based on self-monitoring of glucose — read more about the devices used for this on the "Glucometers" page.