The primary job of basal insulin is to keep your blood glucose levels stable during periods of fasting, such as while you’re sleeping. While fasting, the liver continuously secretes glucose into the bloodstream. 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 ensures that your cells are fed with a constant stream of glucose to burn for energy to fuel the body throughout the day.

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). This insulin is administered once or twice daily, usually mixed with mealtime insulin either in the morning, before your evening meal, or both. It works hardest in the 4 to 8 hours after injection, and starts waning after about 16 hours.
  • Long-acting insulin. Two types of this insulin currently on the market are detemir (Levemir) and glargine (Lantus). This basal insulin begins working 90 minutes to 4 hours hours after injection and remains in your bloodstream for up to 24 hours. It may start weakening a few hours earlier for some people, or last a few hours longer for others. There isn’t a peak time for this type of insulin. It covers at a steady rate throughout the day.

When deciding between intermediate- and long-acting basal insulin, there are many factors to consider. These include your lifestyle and willingness to inject.

You can mix NPH with mealtime insulin, while long-acting basal insulin must be injected separately.

Factors that can affect your insulin dose include body size, hormone levels, diet, and how much, if any, internal insulin is still being produced by your pancreas.


Many people with diabetes like basal insulin because it helps them better manage blood sugar levels between meals, and allows for a more flexible lifestyle.

For example, if you use long-acting insulin, you don’t have to worry about peak times of insulin activity. This means that meal timing can be more flexible. It may also reduce your risk for low blood sugar levels.

If you’re struggling to maintain your target blood sugar levels in the morning, adding basal insulin to your dinnertime or bedtime regimen may help solve this problem.

Dosage Information

With basal insulin, you have three dosage options. Each option has pros and cons:

  • Taking NPH either at bedtime or in the morning, or both: This approach can be valuable because the insulin peaks during the predawn and afternoon hours when it’s needed most. But that peak can be unpredictable, depending on your meals, meal timing, and activity level. This may result in low blood sugar while you’re sleeping, or in low or high blood glucose levels during daytime hours,
  • Taking detemir or glargine at bedtime: The continuous 24-hour flow of these long-acting insulins is one of their main advantages. But, some people find that this insulin wears off faster than 24 hours after injection. This can mean higher blood glucose levels at your 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. 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. Your doctor or endocrinologist can help you decide which dosage is right for you.

Side Effects

Some potential side effects associated with basal insulin include hypoglycemia and possible weight gain (though to a lesser degree compared with other types of insulin).

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

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

Basal insulin is a crucial component for your diabetes management. Working with your doctor or endocrinologist gives you a greater chance at determining which type is best for you and your needs.