Novolin N is an intermediate-acting insulin used to manage blood sugar in people with diabetes. It contains NPH (neutral protamine Hagedorn) insulin, a form of human insulin that works more slowly than mealtime insulins by releasing gradually over several hours. First approved by the FDA in 1991 and manufactured by Novo Nordisk, it remains one of the most affordable and accessible insulins available in the United States.
How Novolin N Works
All insulin helps move sugar from your bloodstream into your cells, where it’s used for energy. What makes Novolin N different from rapid-acting or mealtime insulins is its timing. The insulin is suspended with a protein called protamine, which slows its absorption after injection. This creates a longer, more gradual effect designed to cover your background insulin needs between meals and overnight, rather than the sharp spike of sugar that follows a specific meal.
Novolin N typically begins lowering blood sugar within 1 to 3 hours after injection, reaches its strongest effect around 4 to 12 hours, and continues working for roughly 14 to 24 hours total. That pronounced peak in the middle of its action window is one of its defining characteristics, and it’s an important distinction from newer long-acting insulins that deliver a flatter, more even effect throughout the day.
Where It Fits in Diabetes Treatment
Novolin N can be used for both type 1 and type 2 diabetes, usually as the “basal” (background) layer of an insulin regimen. Many people pair it with a rapid-acting insulin taken at meals, while others with type 2 diabetes may use it alongside oral medications.
Newer long-acting insulin analogs have largely replaced NPH insulin in clinical guidelines. The American Diabetes Association’s 2025 standards note that these analogs have a longer duration, flatter activity profiles, and a lower risk of hypoglycemia, particularly dangerous overnight lows. For people with type 1 diabetes specifically, the ADA recommends insulin analogs over human insulins like Novolin N to minimize hypoglycemia risk.
That said, NPH insulin still has a clear role. Cost is the biggest factor. Novolin N is significantly cheaper than long-acting analogs, and the ADA explicitly acknowledges human insulin as an appropriate option for people facing cost-related barriers to treatment. For many people, affordable insulin they can actually obtain is better than a theoretically superior product they can’t afford.
Cost and Over-the-Counter Access
Novolin N is one of the few insulins you can buy without a prescription in most U.S. states. Walmart sells it under its ReliOn brand at a starting price of $24.88 for a 10 mL vial and $42.88 for a pack of five prefilled pens. The price is the same whether or not you have insurance. For comparison, many long-acting analog insulins can cost several hundred dollars without insurance coverage.
This accessibility makes Novolin N a critical safety net. People who lose insurance, face gaps in coverage, or simply can’t afford newer insulins often rely on it. The tradeoff is that NPH insulin requires more careful timing and monitoring than its modern counterparts, which means switching to it without guidance can be risky.
Available Forms and Concentration
Novolin N comes in two formats: a 10 mL vial designed for use with a syringe, and prefilled FlexPens. Both deliver the standard U-100 concentration, meaning 100 units of insulin per milliliter. The vial contains 1,000 units total. If you’re using the vial, you’ll draw up your dose with an insulin syringe; the pens let you dial your dose and inject without handling a syringe.
The Nocturnal Hypoglycemia Risk
The most significant side effect of any insulin is hypoglycemia, or low blood sugar. With Novolin N, this risk is higher than with newer long-acting insulins, and it’s especially concentrated during overnight hours. That’s because of the pronounced peak in NPH’s activity curve. If you take your evening dose and the peak hits while you’re asleep, your blood sugar can drop without you noticing the warning signs.
Symptoms of low blood sugar include shakiness, sweating, confusion, rapid heartbeat, irritability, and hunger. Severe episodes can cause loss of consciousness or seizures. Because beta-blockers, clonidine, and a few other blood pressure medications can mask these warning signs, people taking those drugs alongside Novolin N need to check their blood sugar more frequently.
Other possible side effects include injection site reactions like redness, swelling, or itching at the spot where you inject. Rotating injection sites helps reduce this. Allergic reactions to Novolin N are rare but possible.
Medications That Affect Blood Sugar Control
A number of common medications can change how well Novolin N works. Some increase its blood-sugar-lowering effect, raising the risk of hypoglycemia. These include ACE inhibitors (used for blood pressure), certain antidepressants like fluoxetine, and high-dose aspirin or other salicylates.
Other drugs push blood sugar higher, potentially making your insulin dose feel inadequate. Corticosteroids (like prednisone), oral contraceptives, thyroid hormones, and certain antipsychotic medications all fall into this category. Alcohol is unpredictable: it can swing blood sugar in either direction. If you start or stop any medication while using Novolin N, more frequent blood sugar checks will help you and your care team adjust your dose.
Storage and Shelf Life
Unopened Novolin N should be stored in the refrigerator between 36°F and 46°F. Once you open a vial or start using a pen, it can be kept at room temperature (59°F to 86°F) for up to 28 days. After that, discard it even if insulin remains, because its potency degrades. Never freeze insulin, and keep it out of direct sunlight or extreme heat.
Before each injection, you need to gently roll the vial or pen between your palms to resuspend the insulin. Novolin N is a cloudy suspension by design. If you see clumps, solid white particles stuck to the glass, or the liquid stays clear after mixing, don’t use it.
NPH vs. Long-Acting Insulin Analogs
The core difference comes down to predictability. Long-acting analogs deliver a steady, nearly peakless level of background insulin over 24 hours or more. Novolin N has a definite peak and a shorter, more variable duration. That peak means your blood sugar is more likely to dip at certain hours and rise at others, requiring more precise meal and dose timing to stay in range.
Clinical trials have consistently shown that long-acting analogs produce fewer episodes of dangerous low blood sugar and fewer overnight lows compared to NPH. They’re also associated with slightly lower A1C levels and less weight gain in people with type 1 diabetes. But these advantages come at a much higher price point, and for people who monitor carefully and time their doses consistently, Novolin N remains an effective option that has managed diabetes successfully for over three decades.