Regular insulin is a short acting, synthetic form of the hormone. The body uses insulin to process sugar that enters the bloodstream as part of the digestive process.

In a person without diabetes, the pancreas creates enough insulin to move the sugar, called glucose, from the blood into cells that use it for energy.

However, diabetes affects this process, which is why some people with diabetes need extra insulin.

Below, learn more about regular insulin and how people use it to manage their diabetes. We also describe dosages, side effects, and other warnings.

a woman taking Regular insulin as an injection in her stomach
A person may take regular insulin to help control blood glucose levels.

Diabetes affects how the body manages blood sugar, or blood glucose, levels.

A person with type 1 diabetes does not produce insulin naturally. A person with type 2 diabetes may not produce enough insulin, or the insulin may not manage their blood glucose levels effectively.

Either type of diabetes puts a person at risk of having too much sugar in their blood, which doctors call hyperglycemia.

Taking regular insulin is one way to help control blood glucose levels in a person with either type of diabetes. Typically, a doctor also recommends:

  • regular exercise
  • a healthful diet
  • other insulin products

Learn more about managing diabetes.

Forms of regular insulin

Regular insulin is available in three forms:

  • an injectable solution
  • an intravenous (IV) solution
  • an inhalable powder

The injectable solution is available under the brand names Humulin and Novolin. There is currently no generic prescription form of either.

A doctor may prescribe long lasting insulin to accompany regular insulin.

Regular insulin comes in three forms, and a doctor will advise about the best option, taking specific factors into account.

People injecting Humulin R or Novolin R should do so approximately before meals. This will give the insulin time to start working.

and have similar dosages and instructions. They come in concentrations of 100 units per milliliter (ml), and both are clear liquids.

A person should only mix the intermediate acting insulin called neutral protamine Hagedorn — or NPH — with Humulin R or Novolin R if a doctor recommends it.

According to product inserts, a person can safely mix Humulin R with Humulin N, and they may mix Novolin R with either Humulin N or Novolin N.

Both Humulin R and Novolin R come in two vial sizes:

To inject the medication, a person draws their dose from the vial and administers the shot to their:

Rotating injection sites may help reduce the risk of lipodystrophy, which involves problems producing and maintaining healthy fat tissue.

Often, a doctor prescribes long lasting insulin to accompany regular insulin, and it is important to closely follow the doctor's instructions regarding when to take each drug.

How much regular insulin a person needs may depend on:

Regular insulin is available by IV, but a person should not attempt to self-administer it. Receive IV insulin only under direct supervision at a medical facility.

Potential adverse effects of regular insulin can range from mild to severe.

Common side effects

A person taking regular insulin may experience:

Low blood sugar is another common side effect of regular insulin, and anyone taking this treatment should be aware of the symptoms.

Low blood sugar symptoms include:

Anyone experiencing more severe side effects should call their doctor immediately.

Serious side effects

Some common severe side effects include:

Low levels of potassium in the blood can cause weakness, muscle cramps, constipation, and tiredness, among other symptoms.

A serious allergic reaction can cause a fast heartbeat, a rash that covers the body, trouble breathing, sweating, and a feeling of faintness, among other symptoms.

Some symptoms of severe low blood sugar include confusion or delirium, sleepiness, seizure, and loss of consciousness.

Some symptoms of heart failure include swelling in feet and ankles, trouble breathing, and sudden weight gain.

A person should receive medical attention for any of these severe symptoms. In an emergency, call 911 or seek immediate medical aid.

Warnings

Doctors also advise about other potential negative effects of regular insulin. Some of these warnings involve:

  • Drug interactions: Various drugs can harmfully interact with regular insulin, and more information is below.
  • Hypoglycemia, or low blood sugar: Regular insulin can cause blood glucose levels to drop dangerously.
  • Infection: Avoid sharing needles with others to minimize this risk.
  • Allergic reaction: A reaction to regular insulin can affect the entire body.
  • Alcohol: Regular insulin can lower blood sugar levels to the extent that drinking alcohol is unsafe.
  • Food interactions: Consuming too many or too few carbohydrates can cause blood sugar levels to spike or dip, and a person taking regular insulin should never skip meals.
  • Other health conditions: Discuss any other ongoing health conditions with a doctor before taking regular insulin.

Learn more about hypoglycemia.

Many different types of drugs can interact with regular insulin. Before starting insulin treatment, a person should let their doctor know about anything that they take on a regular basis, including:

  • vitamins
  • minerals
  • supplements
  • over-the-counter medications

The drug interactions can vary — some cause the insulin to work less well, while others cause side effects to become more severe.

Below, we describe certain interactions and the drugs that can cause them:

Low blood sugar levels

Taking the following medications with regular insulin can cause moderately low blood sugar levels:

Taking the following alongside regular insulin can cause extremely low blood sugar levels:

Fluid retention and heart failure

Taking thiazolidinediones, another type of medication for diabetes, with regular insulin may cause fluid retention and heart failure.

High blood sugar levels

The following medications can cause high blood sugar levels if a person takes them alongside regular insulin:

  • niacin
  • asthma medications, such as corticosteroids and sympathomimetic agents
  • hormonal birth control
  • protease inhibitors