Diabetes Home > Side Effects of NPH Insulin

Low blood sugar and allergic reactions are potentially serious side effects of NPH insulin that should be reported to a healthcare provider immediately. Some of the warnings signs of low blood sugar include blurry vision, cold sweats, and extreme hunger. Other potential NPH insulin side effects include skin thickening or pitting at the injection site, skin reaction at the injection site, and high blood sugar.

An Introduction to Side Effects of NPH Insulin

As with any medicine, side effects are possible with NPH insulin (Humulin® N, Novolin® N). However, not everyone who takes the drug will experience side effects. In fact, many people tolerate it quite well. If side effects do occur, they are often minor and either require no treatment or can easily be treated by you or your healthcare provider. However, very serious side effects can occur, especially if you take too much NPH insulin.
(This article covers many, but not all, of the possible side effects with NPH insulin. Your healthcare provider can discuss a more complete list of NPH insulin side effects with you.)

Serious NPH Insulin Side Effects: Warning Signs

Some side effects with NPH insulin are potentially serious and should be reported immediately to your healthcare provider. Some of the warning signs of these serious side effects include:
  • Signs of an allergic reaction, such as:


    • Itching
    • An unexplained rash
    • Hives
    • Swelling of the mouth or throat
    • Wheezing or other difficulty breathing


  • Symptoms of low blood sugar, such as:


    • Cold sweats
    • Shakiness
    • Difficulty speaking
    • Sweating
    • Dizziness
    • Changes in behavior, such as irritability or mood swings
    • Loss of coordination
    • Extreme hunger
    • Blurry vision
    • Confusion
    • Seizures
    • Unconsciousness.


Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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