Comprehensive medication guide to Insulin, Human Isophane including estimated pricing, availability information, side effects, and how to find it in stock at your local pharmacy.
Estimated Insurance Pricing
$0–$35/month copay for most covered plans; capped at $35/month under the Inflation Reduction Act for Medicare Part D beneficiaries (effective January 2024); Tier 1–2 on most commercial formularies.
Estimated Cash Pricing
$148–$158 retail per 10 mL vial (Humulin N or Novolin N); as low as $25/vial OTC at Walmart (ReliOn Novolin N); approximately $47–$51/vial with GoodRx or SingleCare coupons for a 30-day supply.
Medfinder Findability Score
72/100
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Insulin, human isophane — commonly known as NPH insulin — is an intermediate-acting human insulin used to improve blood sugar control in people with Type 1 and Type 2 diabetes mellitus. NPH stands for Neutral Protamine Hagedorn, named after the scientist who created this formulation in 1946. It is one of the oldest insulin preparations still in widespread use today and is included on the World Health Organization's List of Essential Medicines.
NPH insulin is available under the brand names Humulin N (Eli Lilly, FDA-approved 1982) and Novolin N (Novo Nordisk, FDA-approved 1991). Walmart sells Novolin N under the private label ReliOn Novolin N for approximately $25 per vial — available over-the-counter without a prescription in most states.
In 2020, insulin isophane was the 221st most prescribed medication in the United States, with more than 2 million prescriptions. It is injected subcutaneously (under the skin) once or twice daily and is available as 10 mL vials and prefilled pens (KwikPen for Humulin N, FlexPen for Novolin N), all at 100 units/mL (U-100).
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Insulin, human isophane works through the same fundamental mechanism as all insulins: it lowers blood glucose by stimulating glucose uptake in skeletal muscle and fat tissue, and by inhibiting the liver from producing and releasing excess glucose (hepatic glucose production). It also inhibits lipolysis (fat breakdown), inhibits proteolysis (protein breakdown), and enhances protein synthesis.
What makes NPH insulin intermediate-acting is its formulation: regular insulin is combined with protamine protein and zinc at neutral pH, forming insoluble insulin-protamine crystals. When injected subcutaneously, these crystals dissolve slowly over time, releasing insulin gradually into the bloodstream. This delayed release gives NPH its characteristic onset of 1-3 hours, peak effect at 4-12 hours, and duration of 12-24 hours — making it useful as a basal (background) insulin taken once or twice daily.
NPH appears as a white, cloudy suspension because of these protamine-zinc crystals. It must be gently rolled 10 times before each use to resuspend the crystals uniformly. Inadequate resuspension is a major contributor to the day-to-day variability in NPH's pharmacokinetics — a known limitation compared to modern long-acting analogs like insulin glargine, which have flatter, more predictable profiles.
100 units/mL (U-100) — Injectable suspension — 10 mL vial
Standard vial formulation for use with syringe and needle
100 units/mL (U-100) — Prefilled pen — 3 mL KwikPen (Humulin N) / FlexPen (Novolin N)
Prefilled single-patient-use pen; KwikPen dials in 1-unit increments
As of 2026, standalone NPH insulin (Humulin N and Novolin N) is not on the FDA's official Drug Shortages list. National supply from both Eli Lilly and Novo Nordisk has been maintained, and the OTC Walmart ReliOn Novolin N option provides a consistent low-cost fallback. Overall availability is moderate to good — earning a Findability Score of 72/100.
Despite this relatively stable national supply, patients regularly experience pharmacy-level stockouts. Individual pharmacies may carry one brand but not the other, or vials but not pens. Demand spikes occur when other basal insulins face shortages — driving patients and providers back to NPH as an affordable alternative. ASHP issued a shortage bulletin for combination NPH+Regular insulin products in 2024, which impacted localized NPH access as well.
If you are struggling to find NPH insulin at your local pharmacy, medfinder calls pharmacies near you to check which ones have your medication in stock — saving you the frustration of calling pharmacies yourself. For patients who need immediate access without a prescription, Walmart's ReliOn Novolin N (~$25/vial OTC) is often the most consistently available option.
Since insulin, human isophane is not a controlled substance, any licensed prescriber can recommend or prescribe it without special DEA registration. In most U.S. states it is even available over-the-counter, meaning no prescription is technically required for purchase. However, medical supervision is strongly recommended for safe dosing and ongoing diabetes management.
Provider types who routinely prescribe NPH insulin include:
NPH insulin can also be prescribed through telehealth visits. Since it is not a controlled substance, telehealth providers face no additional restrictions in prescribing it. Many platforms — including Teladoc, MDLive, Amwell, and specialized diabetes telehealth services — can prescribe and manage NPH insulin remotely.
No. Insulin, human isophane (NPH insulin) is not a controlled substance. It is not scheduled by the DEA under the Controlled Substances Act and carries no special prescribing restrictions, DEA registration requirements, or refill limitations associated with controlled medications.
In most U.S. states, NPH insulin is actually available over-the-counter — sold "behind the counter" at pharmacies without a prescription. Walmart sells it as ReliOn Novolin N for approximately $25/vial. While no prescription is required to purchase it, NPH insulin should always be used under the supervision of a healthcare provider for appropriate dosing and diabetes management. Any licensed prescriber — including MDs, DOs, NPs, and PAs — can prescribe NPH insulin without special DEA authorization.
The most common side effects of NPH insulin include:
Serious side effects requiring immediate medical attention:
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Insulin Glargine (Lantus, Basaglar, Semglee, Toujeo)
Long-acting basal insulin analog with a flatter, more predictable pharmacokinetic profile and lower nocturnal hypoglycemia risk vs NPH. Most widely used long-acting basal insulin in the US. Available in biosimilar forms (Basaglar, Rezvoglar). Manufacturer savings programs cap cost at $35/month.
Insulin Degludec (Tresiba)
Ultra-long-acting basal insulin with duration over 42 hours and very low hypoglycemia risk. Once-daily dosing with flexible timing. More expensive than NPH or glargine; experiencing intermittent supply constraints as of early 2026.
Regular Human Insulin (Humulin R, Novolin R)
Short-acting human insulin; can be mixed with NPH in the same syringe. Also available OTC at Walmart (~$25/vial). Used as a mealtime insulin, not a basal insulin. Sometimes used as a temporary bridge if NPH is unavailable.
Insulin Detemir (Levemir)
Long-acting basal insulin analog. Novo Nordisk phased out Levemir in the US by end of 2024. No longer a recommended alternative due to market withdrawal.
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Beta-blockers (propranolol, metoprolol, atenolol, carvedilol)
moderateBeta-blockers mask early hypoglycemia warning signs (tachycardia, shakiness), making it harder to recognize low blood sugar. Sweating may still occur. Increase blood glucose monitoring frequency.
Corticosteroids (prednisone, methylprednisolone, dexamethasone)
moderateSteroids significantly raise blood glucose, often requiring substantial increases in insulin dose (50-100% or more) during treatment. Notify prescriber when starting any steroid course.
Thiazolidinediones (pioglitazone, rosiglitazone)
moderateCombination with insulin can cause dose-related fluid retention leading to or worsening heart failure. Monitor for signs of heart failure (edema, dyspnea, weight gain).
Other antidiabetic agents (metformin, sulfonylureas, GLP-1 agonists, SGLT-2 inhibitors)
moderateAdditive blood sugar-lowering effect increases hypoglycemia risk. Dose adjustments may be needed when adding or stopping combination agents.
ACE inhibitors and ARBs (lisinopril, losartan, valsartan)
minorMay enhance insulin sensitivity and lower blood sugar, increasing hypoglycemia risk.
SSRIs (fluoxetine, sertraline)
moderateSome antidepressants can enhance the hypoglycemic effect of insulin. Monitor blood glucose when starting or stopping SSRIs.
Alcohol
moderateAlcohol inhibits hepatic glucose release and can cause delayed hypoglycemia hours after drinking. Impairs ability to recognize hypoglycemia symptoms. Never drink on an empty stomach with NPH insulin.
Antipsychotics (olanzapine, clozapine, quetiapine)
moderateSecond-generation antipsychotics can cause insulin resistance and raise blood glucose, potentially requiring insulin dose increases.
Insulin, human isophane (NPH) has been a cornerstone of diabetes management since 1946. While modern long-acting analogs have largely replaced NPH as the first-line basal insulin for Type 1 and many Type 2 patients, NPH remains clinically appropriate and is one of the most cost-accessible insulins available. The Walmart OTC option (~$25/vial, no prescription) makes it uniquely accessible for patients struggling with insulin affordability — a real-world advantage that analogs cannot match at that price point.
Patients using NPH should be educated on: proper resuspension technique before each injection (gentle rolling, not shaking), the risk of nocturnal hypoglycemia with bedtime dosing due to NPH's 4-12 hour peak, the importance of rotating injection sites to prevent lipodystrophy, and keeping a fast-acting glucose source and ideally a glucagon emergency kit on hand at all times.
If you are struggling to find NPH insulin in stock at a pharmacy near you, medfinder calls pharmacies on your behalf to find which ones can fill your prescription — saving you time and frustration. Your insulin access matters, and we are here to help.
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Our medication guides are researched and written to help patients make informed decisions. All content is reviewed for accuracy and updated regularly. Learn more about our standards
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