Insulin Therapy

Insulin was discovered in the early 1920s by Banting, Best, Collip, and McLeod. Who exactly contributed what to the discovery of insulin was hotly contested by them back then and remains contested to this time. The book by Michael Bliss - The Discovery of Insulin - provides a fascinating account of the discovery and the controversy.

Do I Really Need To Take Insulin?

This is one of the questions I get asked most often by someone with type 2 diabetes for whom I (or another physician) has recommended insulin therapy. (People with type 1 diabetes always require insulin.) 

If you have type 2 diabetes, your pancreas gradually loses its ability to make insulin and thus, with the passage of time, non-insulin medications (that is, oral medications and non-insulin injectable medicines) gradually lose their effectiveness and insulin often becomes required. At least 1/2 (and maybe considerably more) of all people with type 2 diabetes will eventually need insulin therapy. This is not your fault! You can find out more about this here.

What are the types of insulin?

These are the types of insulin and their properties:

(Adapted from NEJM, 352;2 and other sources)

There are also premixed insulins available which are a mixture of two different insulins (in the following table ~NPH means that the insulin in question is very similar to NPH in the way it works):

Which insulin should I take?

If you have type 1 diabetes then in almost all cases you should either use an insulin pump or you should take a longer-acting insulin (NPH, Levemir, or Lantus) once (sometimes twice) daily and a rapid-acting insulin (Apidra, Humalog, or NovoRapid) before each meal.

If you have type 2 diabetes and your main problem is an elevated blood glucose when you awaken (something called the dawn phenomenon) then taking NPH, Lantus, or Levemir, once daily, at bedtime is usually the best choice.

If you have type 2 diabetes and your blood glucose levels are elevated throughout the day (despite taking your non-insulin therapies) then the best insulin choice for most people is to take a longer-acting insulin (NPH, Levemir, or Lantus) once daily and a rapid-acting insulin (Apidra, Humalog, or NovoRapid) before those meals that are causing your after-meal blood glucose to be elevated. Alternatively, some people are sufficiently managed using a premixed insulin before breakfast and before dinner. (Premixed insulin therapy is best reserved for those people whose lives are remarkably consistent day-to-day in terms of when you get up and go to sleep, the type/intensity/duration of exercise, the meals you eat and the timing of your meals, and so on.)


Should I use NPH insulin or, instead, Lantus or Levemir insulin?

NPH is a 'tried and true' insulin that is very effective. It's main drawback is that, compared with Lantus or Levemir, NPH is much more likely to cause hypoglycemia (especially overnight). If you are taking NPH insulin and you are having problems with hypoglycemia you should speak to your health care providers to see if swithcing to Lantus or Levemir would be a good choice for you.


Should I use regular insulin or, instead, Apidra, Humalog, or NovoRapid?

Apidra, Humalog, and NovoRapid insulins provide superior blood glucose control to regular insulin. Therefore, for most people, Apidra, Humalog, and NovoRapid are preferred.


How do I adjust my insulin dose?

If you are being treated with insulin, in order for you to achieve the best possible blood glucose control it is essential that you learn how to adjust your insulin doses. Unlike the great majority of prescription drugs, insulin is not to be taken in a fixed dose day-to-day. Think of it this way; if you are giving yourself insulin, it is to replace what your pancreas should be doing, but is unable to. A normal pancreas makes a different amount of insulin every day so you need to do this also.

Learning how to adjust one’s insulin dose isn’t easy, but it is definitely do-able. The single most important step in learning how to adjust your insulin dose is to be taught this skill by an expert like a diabetes educator or a physician who specializes in diabetes.

Of the many factors involved in determining your insulin dose, these four are especially important:

  • What your blood glucose level has been running for the preceding several days.
  • What your blood glucose level is at the moment you’re about to give your dose.
  • What food (especially, carbohydrates), if any, you’re about to eat.
  • What exercise, if any, you’re about to do.

The most common exception to the rule about needing to take a different amount of insulin day-to-day is the person whose life (eating, activities, stress level, etc) is remarkably consistent and whose blood glucose levels are consistently within the target appropriate for them. In this case, taking the same insulin dose day-to-day may work just fine. (The group of people for which this is most likely to be the case are people who are both elderly and sedentary.)

Although learning how to adjust your insulin dose requires some work, following some basic principles will get you quickly headed in the right direction:

If you are taking NPH, Lantus or Levemir insulin at bedtime:

 If your blood glucose is above target before breakfast, increase the dose of your bedtime NPH, Lantus or Levemir by 1 unit nightly until your before-breakfast blood glucose is in target (4 to 7 mmol/L). (This does not apply if the reason your blood glucose is up before breakfast is because you treated an overnight low.) Do not make the ever-so-common mistake of adjusting your dose of NPH, Levemir, or Lantus bedtime insulin based on your bedtime blood glucose level. Your bedtime blood glucose level, regardless of how elevated, has no bearing on what dose of bedtime NPH, Levemir, or Lantus insulin you need! If your bedtime reading is high this is dealt with by adjusting other aspects of your therapy.

If you are taking Apidra, Humalog or NovoRapid (called NovoLog in some countries) before your meals, determine your dose based on:
  • Your blood glucose before the meal. The higher the reading the more insulin you will need in order to bring your blood glucose level down (this is called a correction factor).
  • Your blood glucose levels the past few days after that meal. If they are running above target (target is usually 5 to 10 mmol/L) then you will need a higher dose.
  • How much carbohydrate (apart from fiber) you’re about to eat.
  • Other factors may also be need to be considered such as what exercise you’re about to do (you do exercise, don’t you?), whether you’re going to be drinking some alcohol, etc.

Sound complex? Well, it is complex. But if your lifestyle (food choices, activities, etc) is pretty consistent day-to-day then it can be pretty straightforward. Here’s an illustration…let’s say the following table illustrates your average readings (and insulin doses) for the past few days:



2hours after breakfast

Before lunch

2 hours after lunch

Before supper

2 hours after supper


Blood glucose








Insulin Dose

Humalog  5 units


Humalog  9 units


Humalog  6 units


Lantus   12 units

So what do you notice about the preceding values? You likely observed that this person’s blood glucose readings are within target except for after breakfast and before lunch. Solution? Well, the first thing is to make sure breakfast doesn’t consist of 8 pancakes washed down with 4 Tim Horton’s “double doubles” in which case it’s not your insulin that needs changing; it’s your diet! Anyhow, trusting your breakfast is reasonably healthy, if your blood glucose is, like in the preceding illustration, too high after breakfast (and, in this case, carrying over to the before-lunch period of time) then what you need is more insulin with your breakfast. So, in this example, taking 5 units of Humalog isn’t enough you should increase your dose by 1 unit daily until your after-breakfast blood glucose is within target.

If you are taking premixed insulin (such as 30/70…called 70/30 in the US) before breakfast (and before supper):

Adjusting premixed insulin can be easy or tricky. If you are taking premixed insulin before breakfast and your blood glucose is consistently too high all day (including before lunch and before dinner) then you need to increase your dose daily until your readings are in target. Conversely, if your readings are consistently too low all day then you need to progressively reduce your dose.

Similarly, if you are taking premixed insulin before supper and your blood glucose is consistently too high in the late evening, overnight, and before breakfast, then you need to increase your dose daily until your readings are down into target.

But what about the situation where your blood glucose is, for example, good before lunch, but too high before dinner? If you increase your morning premixed insulin dose (as you attempt to bring down your dinner-time reading) you’ll end up going too low before lunch. That’s the main problem with premixed insulin; by definition its premixed with a short-acting insulin and a longer-acting insulin and so if you need more of the one and not of the other you’re stuck. That’s why for most people who require insulin (and for virtually all people with type 1 diabetes) I prefer using a rapid-acting insulin before meals and a longer-acting insulin at bedtime; this gives infinitely more flexibility when it comes to adjusting insulin doses.