What Is NPH Insulin?

NPH insulin is an older type of synthetic insulin that helps people with diabetes control their blood sugar. It’s typically injected once or twice a day at regular times and is designed to deliver a steadier release of the drug over a longer period of time than faster-acting insulin.

NPH insulin has a less steady effect than newer types of long-acting insulin, and may carry more risk of low blood sugar. It can still be an effective component of diabetes care, and is generally available at a lower price and without a prescription.

“In people without diabetes, a small amount of insulin is released throughout the day to keep the blood glucose at a steady level," says Joshua J. Neumiller, PharmD, CDCES, president of healthcare and education at the American Diabetes Association. “To mimic this, people with type 1 diabetes and many people with type 2 diabetes take basal insulins to keep the blood glucose steady throughout the day. NPH insulin can be used twice daily to achieve this goal.”

“There is little difference between these products, and if people switch from one product to another, they typically will not notice a difference,” says Dr. Neumiller.

“The main challenges with NPH insulin are the need to inject it more frequently and the increased risk for hypoglycemia when compared to newer long-acting insulins,” says Neumiller.

“Newer long-acting insulin products have a relatively flat glucose-lowering effect, but NPH does have a discernible peak effect and it tends to wear off before the next dose is given,” says Neumiller. “This can lead to additional variability in its action relative to newer long-acting insulins.”

NPH insulin is considered inferior to newer basal insulins, but some people still use it because they’re comfortable with the familiarity of it. It also is available in premixed formulations, which can be convenient.

“It can also be mixed with regular insulin in the same syringe and is well understood by many longtime users,” says Tom Wadsworth, PharmD, an associate professor and the dean of L.S. Skaggs College of Pharmacy at Idaho State University in Pocatello.

NPH insulin is also available in pharmacies without a prescription, but you won’t find it on the store shelves: You need to ask the pharmacist for it. Because it’s more affordable and accessible, some people who use insulin to manage diabetes use it as a backup option if they find themselves without access to their usual supplies.

If you’re switching between NPH insulin and a newer long-acting insulin, you will need to adjust your dosage and injection timing. NPH insulin should only be used under the care of a diabetes healthcare provider

One of the biggest concerns of NPH insulin is the risk for low blood sugar, and Wadsworth says it requires strict attention to timing and food intake to help prevent that from happening.

• Low potassium, which can lead to abnormal heart rhythms and fatigue
• Allergic reactions, including swelling in the face and neck or skin rashes
• Weight gain
• Scar tissue at the injection site

• NPH insulin is an intermediate-acting, man-made insulin used to manage blood sugar levels. It’s an older formulation than other insulin medications, and it’s typically taken twice a day.
• Unlike newer, long-lasting insulins, NPH has a peak effect and a shorter duration of effectiveness, which requires stricter dosage timing and poses a higher risk of low blood sugar. But it is a safe and effective medicine if used properly.
• NPH insulin is more affordable than newer medications, and it can be purchased at a pharmacy without a prescription.