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.
NPH insulin, a man-made, intermediate-acting insulin, is injected into the body for the treatment of type 1 or type 2 diabetes. This insulin acts slowly to lower blood sugar levels in people with diabetes for 14 to 24 hours. It’s generally used as a basal insulin to manage blood sugar between meals and overnight.
“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.”
NPH has a cloudy appearance and needs to be mixed before it’s used. The effects last around 14 to 24 hours and are at their most powerful around four to six hours after injection.
NPH is administered with an insulin pen or syringe to the stomach, thighs, or upper arms. Humulin N is one brand of NPH insulin produced by Eli Lilly and Company, and Novo Nordisk makes Novolin N.
“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.
Other options that might contain NPH insulin are premixed insulins that contain more than one type of insulin. For example, Humulin 70/30 has both regular insulin, an older generation of fast-acting insulin, and NPH insulin. Premixed insulin options may help lower the number of injections people need to administer.
NPH insulin is an older form of insulin, and today it is usually not the first choice for blood sugar management. It is typically administered twice a day, as opposed to newer long-lasting insulins, degludec (Tresiba) and glargine (Lantus), which may only require one daily dose. NPH insulin also necessitates more strict timing of the doses, because its strength peaks hours after injection, a moment which may increase the risk of low blood sugar (hypoglycemia), especially overnight.
“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.”
Over time, there’s been a shift away from NPH insulin to newer options. One study found that NPH and regular insulin are used by only 2.6 percent of people who use insulin.
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.
The low cost of NPH insulin, around $25 a vial, is another draw. Newer forms of insulin can be prohibitively expensive, especially for those without insurance. But there are programs that can lower the costs. In the United States, some people who are uninsured may be able to get insulin for free, and Medicare and around half of U.S. states have a maximum out-of-pocket cost for most types of insulin, which is typically $35 for a 30-day supply.
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.
“People taking insulin should have a plan that incorporates strategies to prevent and treat hypoglycemia,” says Neumiller. That can include regular A1C testing, the use of a continuous glucose monitor, or regular finger pricks throughout the day. Regular meals, at the same time each day, may also help prevent low blood sugar for people who take NPH insulin.
NPH insulin also needs to be mixed before it’s injected to be effective. An improperly prepared injection could lead to ineffective or unpredictable glucose changes.
Other side effects of NPH insulin include:
Low potassium, which can lead to abnormal heart rhythms and fatigue
Allergic reactions, including swelling in the face and neck or skin rashes
It can be potentially dangerous to combine NPH with other medications, so make sure all your healthcare providers know which prescriptions you take.
Make a point of rotating where you administer the medicine to prevent injuring the injection site. Dosing in the same place on your body can lead to lipohypertrophy, which is when a lump of fatty tissue develops underneath the injection site, disrupting insulin absorption.
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.
