Know Your Insulins and their Timing

A good way to improve glucose levels is to track the peaks and drops in your glucose and relate how the peak and action times of your insulins correspond to low or high patterns in your glucose. Identify your glucose patterns (they ARE there!), and work to understand when each of your insulins is active. This allows you to adjust your insulin doses or food choices to stop unwanted ups and downs in your readings.

The table below shows the start, peak, and end times for various insulins.

When Does My Insulin Peak and How Long Does It Last?
Action Times for Insulins
Insulin Starts Peaks Ends Low most likely at: Usage
Hum/Nov/Apidra 10–20 m 1.5–2.5 h 4.5–6 h 2–5 h covers meals and lowers high BGs
Regular 30–45 m 2–3.5 h 5–7 h 3–7 h covers meals and lowers high BGs
NPH 1–3 h 4–9 h 14–20 h 4–12 h intermediate peaking and action time
Lantus 1–2 h 6 hr 18–26 h 6–10 h minimal peaking and longer-acting background insulin action
Levemir 1–3 h 8–10 18–26 h 8–14 h minimal peaking and longer-acting background insulin action
Toujeo 2 h none 36 h varies very flat, long-acting background insulin action
Tresiba 2 h none 42 h varies very flat, long-acting background insulin action


Rapid Insulins

Humalog (lispro), Novolog (aspart), and Apidra (glulisine) insulins cover meals and affect the glucose afterward. Their glucose-lowering activity starts to work about 20 minutes after they are taken, with a gradual rise in activity over the next 1.75 to 2.25 hours, then falling over the next 3 hours. These insulins lower the glucose for 5 hours or a bit longer. Although their “insulin action times” are often quoted as 3-5 hours, the actual duration of insulin action is 5 hours or more. See our article Duration of Insulin Action for more information on this important topic.

These so-called “rapid” insulins are slower than the digestion of most meals where the glucose peaks within an hour and digestion is complete within 2-3 hours. The best-kept secret on stopping post-meal spiking is to take the injection or bolus earlier before the meal and to eat more low glycemic carbs that digest more slowly.

Regular Insulin

The much older Regular insulin has a slightly slower action with a slightly higher risk for nighttime hypoglycemia. It works well for people who take Symlin or who have gastroparesis (delayed digestion). It is also much less expensive at places like Walmart.

Long-Acting Insulins

Though often thought of as being 24-hour insulins, Lantus (glargine) and Levemir (detemir) are actually 18 to 26-hour insulins. About a third of users do not get a full 24 hours of action from these insulins. Those who experience shorter activity times may also notice more peaking in activity and tend to experience lower glucose readings about 6 hours after the injection. A larger peak in activity at 6 to 8 hours is associated with a shorter action time, and vice versa. Anyone who does not take their long-acting insulin at about the same time each day can also experience gaps and stacking of insulin with a single injection a day. Smaller doses of these insulins are also often associated with less than 24 hours of activity.

If Lantus or Levemir “wears out” before the day is done, unexplained highs often occur before or soon after the next dose is given. If one injection is given in the morning, high readings may occur before breakfast due to the lessening activity from the previous dose.

Splitting doses of “24-hour” insulins into two equal doses with half taken in the morning and the other half taken in the evening even out dosing gaps and minimize peaking. After splitting a single dose of Lantus or Levemir, many people find they have better readings.

Both Toujeo (U-300 glargine) and Tresiba (degludec) are the longest-acting insulins (36 hrs or more) and have little or no peak in activity. They provide a very flat and very consistent action from day to day.


The old NPH (Neutral Protamine Hagedorn) insulin has a shorter action with more peaking than Lantus or Levemir. This can be useful at times. For example, if a teen or young adult has a Dawn Phenomenon or someone with Type 2 diabetes sees their glucose rise in the early morning hours due to release of more free fatty acids during sleep, NPH can be taken at bedtime to provide the extra insulin needed during the late morning hours. Bedtime NPH can be combined with an injection of Lantus or Levemir at breakfast to cover the daytime hours.

A bedtime dose of NPH can also be combined with two daytime injections of NPH before breakfast and lunch to reduce the number of injections required in a day. For those who use a syringe, NPH can also be combined with the rapid insulin taken for a meal into a single injection. Like Regular insulin, NPH is much less expensive. If cost is a concern, try splitting the current dose of Lantus or Levemir into 3 equal injections of NPH each day. Most people find this provides very stable basal insulin action once the total dose is dialed in, along with any increase in the bedtime dose that may be needed to offset a Dawn Phenomenon or Type 2 diabetes.