What is this stuff I have to take? Is it a drug? Will it make me better, so I don't have to take it anymore? What does it do? Why can't I just drink it, or take a big shot once a month? And why are there so many different types? Will there ever be something better?

Insulin is a hormone, normally produced in sufficient amounts by the healthy human pancreas. Its role is to facilitate the final digestion of glucose by the human body. When insulin is lacking (diabetes), glucose remains undigested in the blood. The body isn't being fed, and the high blood sugar can cause damage, the ramifications of diabetes.

The two major types of diabetes (type 1 and type 2, IDDM and NIDDM) are separated by presence of insulin. The pancreas of the type 1 diabetic has ceased producing insulin, and insulin must be injected. This injected insulin is a replacement, and, barring the transplantation of a healthy pancreas, will need to be continued for life.

The type 2 (NIDDM) diabetic has an impaired insulin supply. He or she doesn't have enough, or has some difficulty assimilating it (insulin resistance), or both. Lifestyle and diet changes, and oral medications, some of which stimulate the failing pancreas to produce more insulin, are used in treatment. Many veteran type 2 diabetics find their insulin supply, already impaired, has lessened to the point where they need to inject insulin.

Insulin cannot be taken by mouth because it is digestible. Oral insulin would be obliterated in the stomach, long before it reached the bloodstream where it is needed. Once injected, it starts to work and is used up in a matter of hours. Depending on a number of factors, individuals vary insulin volume, type, and frequency, to optimize blood glucose management.

That there are so many different formulations of insulin is partly intentional, and partly an accident of history. Before insulin, diabetics just died. When the hormone became available in the 1920s, doctors realized patients' needs differed. As newer formulations of insulin became available, it was discovered that the best blood sugar control was achieved by use of a mix of insulins of different duration and time of onset (as described below). The earliest insulins were made from animals ("animal source") but newer types are made "in the test tube" ("recombinant DNA origin"). The existence of so many different insulins helps the doctor tailor a dosage best for a specific individual. As new types of insulin are invented, they will help achieve an even better "fit."

Many patients have specific questions about insulin use. Some of the most common are listed below:

Q: How long before a meal should insulin be injected?

A: With "Regular" insulin, it is recommended you inject 30 minutes before meals. With Humalog (Eli Lilly & Co.'s trade name for quick-acting Lispro insulin analog), a 10-minute wait is sufficient. Insulin works far better when given sufficient time to do its job. Diabetes self-management requires keeping to the established schedule. Too much time, or too little, will cause problems. If you wait after injection for your blood glucose to drop, before you start to eat, you may limit the "glycemic excursion" (blood sugar rise) that follows a meal, but you are taking chances with possible hypoglycemia.

Q: Do insulin absorption rates vary from one person to another?

A: Yes. Some diabetics get 16-20 hours out of an NPH/Lente shot, while others get 8-12 hours. An individual can experience day to day variation of up to 50%, with the same dose. The same person, with the same dose and technique, may also see a day to day variation of 25-50% in time of insulin peak action.

Q: Does exercise affect absorption?

A: Yes. Exercise of a given muscle area after injection of insulin into that area will cause the insulin to be absorbed faster. Exercise in general burns up blood glucose, lessening the need for insulin to digest it, thus increasing the effect of injected insulin. Massage of the injection site after injection can help speed absorption.

Q: Which injection technique makes the insulin work faster—Subcutaneous or Intramuscular?

A: Intramuscular (IM) injection is faster. However, IM injection is not for regular use, and has its risks. Your doctor may use it in special situations, but day to day insulin injections should all be of the subcutaneous (SubQ) type. Mixing the two would inject another variable into your diabetes control.

Q: Does being a smoker change insulin absorption?

A: Yes. Along with all the other damage it does, smoking decreases insulin absorption.

Q: What are the absorption differences between insulin injection sites?

A: The abdomen is the fastest, followed by arms and thighs (no data available on absorption rate in the buttocks). These differences may be used to prolong or speed up the effect of insulin for special circumstances, but it is best to keep injecting within one anatomical area, for consistency in time of onset.

Q: Does the speed with which I push the plunger of the syringe make any difference?

A: No, velocity does not make any difference.

Q: Does the angle of injection make any difference in absorption?

A: The angle of injection (45 to 90 degrees) makes no difference.

Q: Does skinfold thickness affect absorption?

A: The more fat present in the injection site, the slower the absorption.

Q: I want to switch from animal-source to human insulin. Is there much difference?

A: Human (recombinant DNA) insulins work faster than animal-source insulins of the same type, so you may need to recompute your daily doses. Talk to your doctor.

Q: Why is "rolling" the insulin vial before drawing up a shot preferable to shaking it?

A: The recommendation is to roll only the suspension insulins, NPH and Lente. There is no need to agitate Regular insulin. Shaking instead of rolling the vial would produce air bubbles.

Q: How should insulin be stored?

A: Insulin vials should be kept refrigerated until you are ready to start using them. Then they need to be kept in a cool place, away from extremes of temperature. Insulin is fragile, and exposure to extreme heat, or freezing, can destroy its efficacy.

Q: How can I have a more flexible insulin regimen?

A: Some people use sliding scales and algorithms for the regular dose, according to the amount of food taken at the time. Use of such a technique requires thorough familiarity.

Q: What is "buffered" insulin?

A: Buffered Regular insulin is for use in insulin pumps. It acts just like other "R" insulins, but contains a buffering agent to make it more stable for such use. Some folks use conventional, unbuffered, Regular in their pumps, but the manufacturers recommend use of the buffered variety.

Q: What are the durations and peak times for the different insulin classes?


Lispro 10 min 1 hr 4 hr 2-4 hr

Regular 20 min 3-4 hr 8 hr 3-7 hr

NPH 1.5 hr 4-10 hr 22 hr 6-13 hr

Lente 2.5 hr 6-12 hr 24 hr 7-14 hr

Ultralente 4 hr 10-18 hr 36 hr 10-22 hr


(This chart is from "Stop the Rollercoaster," by Walsh and Roberts, with further data provided by Eli Lilly & Co. Please Note: Times are approximate, and will vary between individuals!)

Much of the above data were compiled by Arturo Rolla, MD, of Harvard University School of Medicine.