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Different Types of Insulin

Where Insulin Comes From

Almost all of the insulin sold in the United States today is what is known as "human insulin." Developed by scientists, this laboratory-created insulin is made by DNA recombinant technology and is very similar, really identical, to insulin from a human pancreas. It's available in varieties that are designed to start working within just a few minutes or last for many hours, giving insulin users a lot of control over their blood sugar levels. (Before the introduction of human insulins, people used insulin from beef and pork sources.)

Insulin can't be taken as a pill or capsule because the digestive juices in the stomach ruin its effectiveness. Oral insulin pills might be a reality someday, but right now the only way to take insulin is by injecting it directly into the layer of fat just below the skin. Most people inject insulin with a syringe or insulin pen, although other methods are available.

Insulin Strengths: U-40 and U-100

In the United States, insulin is labeled "U-100," which means there are 100 units of insulin per milliliter of fluid in the vial. Some insulin is also available in U-500 strength. This form of insulin is only for people with marked insulin resistance who take doses of more than 200 units per day.

People traveling outside the United States must bring enough U-100 insulin and syringes to last the entire trip, because insulin in some other countries is sometimes sold in U-40 strength. If emergency insulin is needed and the only choice available is U-40 insulin, syringes marked for U-40 should be used as well. Syringes for U-40 insulin have a red cover and red scale, rather than the orange needle cover and black scale of U-100 syringes.

All insulin pens throughout the world are U-100. In an emergency, you can purchase insulin pen cartridges and draw the insulin from them (you don't need to inject air into a cartridge). Since a unit of insulin is always a unit of insulin, you should take the same dose of insulin with either U-100 or U-40. If you need more help, a pharmacist or healthcare professional can assist you in determining the proper dosage.

U-100 insulin syringes have orange caps

U-40 insulin syringes have red caps

Basal and Bolus Insulins

The pancreas naturally secretes insulin in two different ways:

A slow, continuous trickle of insulin that stays at a low level in the blood at all times (known as "basal insulin").
Large bursts of insulin that are released when your blood sugar rises, typically after meals (known as "bolus insulin").

While people with type 1 diabetes need a treatment program that gives them both basal and bolus insulin, the treatment for people with type 2 varies and usually changes over time:

Some people with type 2 diabetes only need basal insulin injections (often just a single shot at bedtime) because their pancreas can still provide the extra insulin needed for meals.
Some people with type 2 diabetes need both basal and bolus insulin.
Many people with type 2 diabetes don't need any insulin injections.

Injections of rapid-acting and short-acting insulins provide the bolus insulin supply needed after meals. Conversely, injections of intermediate-acting and long-acting insulin mimic the body's natural basal supply.