Yes, insulin is a drug. More precisely, it is a prescription medication used to manage diabetes by replacing or supplementing the insulin your body naturally produces. What makes insulin’s classification interesting is that it sits at the intersection of two regulatory categories: for decades the FDA regulated it as a drug, but in 2020 it was officially reclassified as a biologic product, a category reserved for medications derived from living organisms or made using biological processes.
Insulin Is Both a Hormone and a Medication
Your pancreas naturally produces insulin, a hormone that helps cells absorb sugar from your bloodstream for energy. In this form, insulin is simply part of your body’s normal metabolism. When someone with diabetes injects or inhales a manufactured version of insulin, that product is a medication, regulated, prescribed, and dosed like any other drug.
The key difference between the insulin your body makes and the insulin you take as medication is how it reaches your liver. Your pancreas secretes insulin directly into the portal vein, exposing the liver to concentrations two to three times higher than what circulates through the rest of your body. Injected insulin enters through the skin and distributes more evenly, which is why dosing has to be carefully calibrated to mimic what the pancreas would do on its own.
How the FDA Classifies Insulin
Insulin has always been a biologic in the scientific sense. It was originally extracted from pig and cow pancreases in the 1920s. Even after recombinant DNA technology allowed scientists to produce human insulin using bacteria in 1982, the FDA continued regulating insulin as a drug under the Federal Food, Drug, and Cosmetic Act rather than as a biologic under the Public Health Service Act.
That changed on March 23, 2020. Under the Biologics Price Competition and Innovation Act, part of the Affordable Care Act, all insulin products were officially transitioned to biologic product licenses. This wasn’t just a technicality. The reclassification opened the door for manufacturers to develop biosimilar insulins, essentially the biologic equivalent of generic drugs. The goal was to increase competition and bring down costs for patients.
Why Insulin Is Prescribed
People with type 1 diabetes produce little to no insulin, so they depend on insulin medication to survive. Most are treated with a combination of long-acting (basal) insulin and rapid-acting insulin taken around meals, either through injections or a continuous pump. A typical starting dose is around 0.5 units per kilogram of body weight per day, though this varies widely based on age, activity level, and individual response.
For type 2 diabetes, insulin is not always the first treatment. Many people manage their blood sugar with oral medications, diet, and exercise. But insulin becomes necessary when blood sugar is severely elevated (300 mg/dL or higher, or an A1C of 10% or above), when other medications stop working adequately, or when someone is experiencing symptoms like significant weight loss or excessive thirst and urination. Over time, the pancreas in type 2 diabetes may produce less and less insulin, making supplemental insulin increasingly important.
Types of Insulin and How They Work
Not all insulin medications behave the same way. They’re designed to mimic different aspects of your body’s natural insulin release:
- Rapid-acting: starts working in about 15 minutes, peaks at 1 hour, lasts 2 to 4 hours. Taken just before or with meals.
- Short-acting (regular): starts in 30 minutes, peaks at 2 to 3 hours, lasts 3 to 6 hours.
- Intermediate-acting: starts in 2 to 4 hours, peaks at 4 to 12 hours, lasts 12 to 18 hours.
- Long-acting: starts in about 2 hours, has no sharp peak, lasts up to 24 hours. Provides a steady baseline level.
- Ultra-long-acting: starts in about 6 hours, has no peak, lasts 36 hours or longer.
Many people use a combination: a long-acting insulin to cover baseline needs throughout the day and a rapid-acting insulin to handle the blood sugar spike after eating.
How Insulin Is Delivered
The most common method is a subcutaneous injection, meaning a small needle delivers insulin just beneath the skin. Traditional vial-and-syringe setups still exist, but most people now use insulin pens, which are more accurate and easier to handle. Newer “smart pens” can calculate doses, remember when you last injected, and transmit data to your phone via Bluetooth.
Insulin pumps deliver a continuous trickle of rapid-acting insulin through a small tube inserted under the skin. They can be programmed to adjust delivery rates throughout the day and deliver extra doses at meals. Some newer systems pair the pump with a continuous glucose monitor, automatically adjusting insulin delivery based on real-time blood sugar readings. The trade-offs include higher cost, the inconvenience of wearing a device, and a slightly increased risk of skin infections at the insertion site.
Inhaled insulin is also available for mealtime use. It enters the bloodstream through the lungs, starting to work in 10 to 15 minutes. It’s not suitable for everyone. Smokers absorb it too quickly, increasing the risk of dangerously low blood sugar, and users may experience a mild cough or small reductions in lung function.
Risks and Side Effects
Hypoglycemia, or dangerously low blood sugar, is the most common and most serious side effect of insulin. Symptoms include shakiness, sweating, confusion, dizziness, and irritability. In severe cases, it can cause seizures, loss of consciousness, or death. Beyond the immediate danger, repeated episodes of hypoglycemia may increase the risk of dementia years later.
Some groups face higher risk. People with type 1 diabetes are three to four times more likely to experience hypoglycemia than people with type 2 diabetes who use insulin. Adults over 80 have roughly 80% higher risk compared to those aged 65 to 70. Across all age groups, people taking insulin alone (without oral blood sugar medications) are several times more likely to visit an emergency department for a hypoglycemia episode.
Weight gain is another common side effect, since insulin helps your body store energy more efficiently. Injection site reactions like redness, swelling, or fat tissue changes can also occur with long-term use.
What Insulin Costs in the U.S.
Insulin pricing has been a major concern for decades. For Medicare beneficiaries, the Inflation Reduction Act of 2022 capped out-of-pocket costs at $35 for a 30-day supply, effective January 1, 2023. There’s a nuance worth knowing: if your prescription covers more than 30 days but less than 60, your plan can treat it as a 60-day supply and charge up to $70.
The 2020 reclassification of insulin as a biologic product was partly motivated by cost concerns. By allowing biosimilar versions of insulin to enter the market, regulators aimed to create competition that would drive prices down over time. Several biosimilar insulins are now available, and more are in development.
From Animal Extracts to Bioengineered Protein
The insulin available today bears little resemblance to early versions. When Eli Lilly first began producing insulin from animal pancreases in the 1920s, potency varied by as much as 25% from one batch to the next. Purification techniques improved that to about 10% variation, and in the 1930s, researchers in Denmark and Canada figured out how to extend insulin’s duration by adding protamine and zinc.
The real breakthrough came in 1978 when scientists at Genentech used recombinant DNA technology to produce human insulin in bacteria. By 1982, this bioengineered insulin hit the market, eliminating the need for animal-sourced products and dramatically improving consistency. Today’s insulin analogs are further modified versions of this recombinant human insulin, engineered to act faster, last longer, or peak more predictably than the natural hormone.