Humulin R and Novolin R are essentially the same insulin. Both contain regular human insulin made through recombinant DNA technology at a concentration of 100 units/mL, and they share the same onset, peak, and duration of action. The key difference is the manufacturer: Humulin R is made by Eli Lilly, while Novolin R is made by Novo Nordisk.
Same Insulin, Different Labels
Both products are classified as short-acting regular human insulin. They work the same way in your body: lowering blood sugar by helping cells absorb glucose. The onset of action for both is 30 to 60 minutes after injection, they peak at 2 to 4 hours, and their effects last 5 to 8 hours. There is no clinically meaningful difference in how they perform.
The active ingredient is identical. Each milliliter contains 100 units of human insulin produced by genetically engineered bacteria or yeast, depending on the manufacturer’s production process. The inactive ingredients are also very similar. Novolin R, for example, contains glycerol, metacresol (a preservative), zinc chloride, and water for injection, with the pH adjusted to 7.4. Humulin R uses a comparable formulation. Minor differences in excipient quantities exist, but these don’t change how the insulin works.
They Are Not Officially Interchangeable
Despite being functionally the same, the FDA does not classify Humulin R and Novolin R as interchangeable products. Both are licensed as standalone biologics under section 351(a) of the Public Health Service Act, meaning each went through its own independent approval process. Neither is designated as a biosimilar or interchangeable version of the other.
In practical terms, this regulatory distinction matters mostly at the pharmacy. A pharmacist generally cannot swap one for the other without your prescriber’s approval, even though the insulin itself is the same type. If your doctor writes a prescription specifically for Humulin R, the pharmacy will dispense Humulin R unless your doctor authorizes a switch. That said, many providers are comfortable with either product and may write prescriptions that allow substitution.
Availability and Delivery Options
Both insulins come in 10 mL multi-dose vials. Novolin R also comes in a prefilled FlexPen (3 mL per pen, sold in packs of five), which can be more convenient if you prefer not to draw insulin from a vial with a syringe. Humulin R is also available in a U-500 concentration (five times stronger than the standard U-100), designed for people with severe insulin resistance who need very large doses. Novolin R does not have a U-500 option.
Over-the-Counter Access and Cost
One of the most practical reasons people search for these two insulins is cost. Both Humulin R and Novolin R can be purchased over the counter in the United States without a prescription. They’re kept behind the pharmacy counter, so you need to ask a pharmacist directly, but no doctor’s visit or prescription is required.
Novolin R is widely known as the insulin behind Walmart’s ReliOn brand, which has historically been one of the most affordable insulin options in the country. Humulin R is also available without a prescription at many pharmacies, though pricing varies. If you’re paying out of pocket, it’s worth comparing prices at your local pharmacy, as the cost difference between the two brands can be significant depending on the retailer.
Switching Between the Two
If you’re considering switching from one to the other, the transition is straightforward because the dosing is the same unit for unit. A dose of 10 units of Humulin R has the same blood sugar-lowering effect as 10 units of Novolin R. You would not need to adjust your dose when switching between the two at the U-100 concentration.
That said, any time you change insulin products, it’s worth monitoring your blood sugar more closely for the first few days. Individual responses can vary slightly due to differences in how your body interacts with the specific formulation, even when the active ingredient is identical. This is a general precaution with any insulin switch, not something unique to these two products.