Known brand names include Humulin N.
An intermediate-acting human insulin, white and cloudy after mixing, injected under the skin. It lowers blood sugar in adults and children with diabetes and starts later and lasts longer than regular insulin.
Insulin NPH is human insulin combined with protamine, a protein, to form tiny crystals suspended in liquid. This form is absorbed from under the skin more slowly than regular insulin, so it starts later and keeps working longer. Once in the blood, it does the job of the body's own insulin, helping muscle and fat take in sugar and telling the liver to stop making sugar. It also slows the breakdown of fat and protein and moves potassium from the blood into cells.
In a study of healthy people, its strongest effect came at about 6.5 hours after a shot, with a range from 2.8 to 13 hours. Timing varies from person to person and from day to day, depending on the injection site, blood flow, temperature, and activity. Low blood sugar is its most common problem, and the risk is highest when its effect is strongest. If not treated, the shift of potassium into cells can lower blood potassium enough to cause dangerous heart rhythms or paralysis of the breathing muscles.
Insulin NPH, covered here as Humulin N, is an intermediate-acting human insulin for diabetes. In type 1 diabetes the body makes no insulin, and in type 2 the body does not make or use insulin normally, so sugar builds up in the blood. It takes the place of insulin the body would normally make, with the goal of better blood sugar control. Over time, high blood sugar can damage the heart, kidneys, nerves, and eyes and raise the chance of a stroke.
It is used by adults and children, who inject it under the skin of the belly, thigh, upper arm, or buttocks. It is often paired with a mealtime insulin, and it may be mixed in the same syringe with Humulin R or Humalog just before the shot. It is a suspension that must be gently rolled and turned until evenly cloudy before each use. It is never given into a vein or through an insulin pump, and it is not used during an episode of low blood sugar.
Low blood sugar is the side effect people notice most, with shakiness, sweating, dizziness, hunger, confusion, or a fast heartbeat. Skin changes where it is injected, itching, rash, weight gain, and swelling of the hands and feet also happen. The label treats severe low blood sugar that can cause seizures or death as dangerous, along with low potassium, serious whole-body allergic reactions, and heart failure when it is used with diabetes pills called TZDs.