Basal insulin’s primary job is to keep blood glucose levels in check during periods of fasting, including sleeping. While fasting, the liver continuously secretes glucose into the bloodstream, and basal insulin is needed to keep these glucose levels under control.

Without this insulin, your glucose levels would rise at an alarming rate. Basal insulin is responsible for making sure your cells are fed with a constant stream of glucose to burn for energy so they don’t resort to metabolizing fat.

Here’s what you need to know about basal insulin, and why it’s important for managing diabetes.


There are two main types of basal insulin:

  • Intermediate-acting insulin, NPH (Humulin and Novolin), is administered once daily. It works hardest 4 to 8 hours after injection and then starts waning around 16 hours.
  • Long-acting insulin begins working several hours after being injected and remains in the bloodstream up to 24 hours. For some people, it may start weakening a few hours earlier, while it may work a few hours longer for others. There are two kinds: detemir (Levemir) and glargine (Lantus).

Many factors go into deciding between intermediate- and long-acting basal insulin. These include activity level, body size, hormone levels, diet, and how much, if any, internal insulin is still being produced by the pancreas.


Many people with diabetes like basal insulin because it puts them in control of monitoring their glucose levels and allows them to have a more flexible lifestyle.

For example, if you’re someone who enjoys sleeping in or who has an irregular sleeping schedule, using basal insulin can help ensure that your glucose doesn’t fluctuate from not eating breakfast at the same time each morning.

Also, if you’re struggling with monitoring your levels in the morning, adding basal insulin to your dinnertime or bedtime regimen can help solve this problem.

Dosage Information

With basal insulin, there are three dosage options. Each option has its own advantages and disadvantages:

  • Taking NPH at bedtime: This can be valuable because it peaks during the predawn hours when it’s needed most. Still, there are times when that peak is unpredictable, which results in high blood glucose levels during the daytime hours.
  • Taking detemir or glargine at bedtime: The continuous 24-hour flow of these long-acting insulins is one of the main advantages. It’s used once or twice daily and causes a slight elevation 6 to 10 hours after injection. But, some people find that it wears off less than the 24 hours after injection. This can mean higher blood glucose levels at the next scheduled injection.
  • Using an insulin pump: With an insulin pump, you can adjust the rate of basal insulin to coincide with your liver function. One drawback to pump therapy is the risk of diabetic ketoacidosis due to pump malfunction, especially because any slight mechanical problem with the pump can result in you not receiving the correct amount of insulin.

Everyone’s basal insulin needs are different, but an endocrinologist can help you decide which basal insulin dosage is right for you.

Side Effects

Some potential side effects associated with basal insulin usage include:

  • hypoglycemia
  • weight gain
  • bronchitis
  • allergic reactions
  • peripheral edema
  • sinusitis
  • back pain
  • infection
  • coughing
  • cataracts

Certain drugs, including beta-blockers, diuretics, clonidine, and lithium salts, can weaken the effects of basal insulin.

Talk to your doctor and endocrinologist about what medications you’re currently taking and any potentially dangerous drug interactions. 

Basal insulin is a crucial component when it comes to diabetes management. By working with an endocrinologist, you have a greater chance of determining which type will work best for you and your needs.