Insulin therapy is the use of manufactured insulin to replace or supplement the insulin a person’s body can no longer produce in sufficient amounts. It began in 1922 as a crude extract from animal pancreases and has evolved over a century into a range of precisely engineered formulations delivered by pumps, pens, and automated systems. For people with type 1 diabetes, insulin therapy is essential for survival. For many with type 2 diabetes, it becomes necessary when other treatments can no longer keep blood sugar under control.
How Insulin Works in the Body
Insulin is a hormone produced by beta cells in the pancreas. When you eat, rising blood sugar triggers these cells to release insulin into the bloodstream. Insulin’s primary job is to move sugar (glucose) out of the blood and into cells that need it for energy, particularly muscle and fat tissue.
It does this by signaling specialized glucose transporters to move from inside the cell to its outer surface. Think of these transporters as doors that open on the cell membrane. When insulin arrives, more doors open, and more glucose flows in. Without insulin, glucose stays trapped in the bloodstream, starving cells of fuel while blood sugar climbs to dangerous levels. In type 1 diabetes, the immune system destroys the beta cells entirely. In advanced type 2 diabetes, beta cells become exhausted or the body stops responding to insulin effectively, sometimes requiring external insulin to fill the gap.
The Discovery That Changed Everything
Before 1922, a diagnosis of type 1 diabetes was a death sentence. Children placed on starvation diets could survive months, sometimes a year or two, but the disease was always fatal.
In May 1921, a young Canadian surgeon named Frederick Banting and a 21-year-old medical student, Charles Best, began a series of experiments at the University of Toronto. They tied off the pancreatic ducts of dogs, waited for the organ to shrink, then extracted a substance from the remaining tissue. When they injected this extract into a diabetic dog named Marjorie, her blood sugar dropped. The extract worked.
By January 1922, a refined version was injected into a 14-year-old boy named Leonard Thompson at Toronto General Hospital. The early results were rocky, with impurities causing an allergic reaction, but a biochemist named James Collip purified the extract further. The second round worked. Thompson’s blood sugar fell, his symptoms improved, and he went on to live another 13 years. In 1923, Banting became the first Canadian and, at 32, the youngest person to receive the Nobel Prize in Physiology or Medicine.
From Animal Extracts to Synthetic Insulin
For the first six decades, all insulin came from the pancreases of cows and pigs. These animal-derived insulins were effective but far from perfect. Bovine and porcine insulin differ slightly from human insulin in their amino acid structure, and some patients developed allergic reactions or built up antibodies that made the insulin less effective over time.
For roughly 25 years after that first injection in 1922, all available formulations were short-acting. Patients needed multiple injections throughout the day. In 1950, an intermediate-acting formulation called NPH insulin became available, giving patients a longer-lasting option that reduced the number of daily shots. The chemical synthesis of human insulin was achieved in 1974, but turning that into a commercial product took another decade.
The real breakthrough came on October 28, 1982, when the FDA approved Humulin, made by Eli Lilly in partnership with Genentech. This was the first biosynthetic human insulin, produced using recombinant DNA technology, and it was the first medical product of any kind made this way. Instead of grinding up animal pancreases, scientists inserted the human insulin gene into bacteria, which then produced insulin identical to what the human body makes. By the 1980s, biosynthetic human insulins became the commercial standard, and animal-derived versions gradually disappeared from most markets.
Types of Insulin Used Today
Modern insulin therapy relies on formulations designed to mimic the body’s natural insulin patterns. Your pancreas normally releases a small, steady stream of insulin throughout the day (basal insulin) and larger bursts at mealtimes (bolus insulin). Different insulin formulations replicate each pattern.
Rapid-Acting and Ultra-Rapid
These are taken just before or with meals. Standard rapid-acting insulins like aspart begin working in about 15 minutes, peak at one to three hours, and last three to five hours. Ultra-rapid formulations can kick in within five minutes and peak at around 30 minutes, closely matching the speed at which food raises blood sugar.
Long-Acting and Ultra-Long
These provide the steady background level of insulin your body needs between meals and overnight. Insulin glargine, one of the most widely used, has an onset of two to four hours, no pronounced peak, and lasts a full 24 hours. Ultra-long formulations like insulin degludec last up to 42 hours, offering more flexibility in dosing schedules and steadier blood sugar control.
The first rapid-acting insulin analogue became available in 1996. These newer analogs are not simply faster or slower versions of regular insulin. Their molecular structure has been intentionally modified so they absorb differently under the skin, giving patients more predictable results and more freedom in timing meals.
How Insulin Therapy Is Structured
Most people with type 1 diabetes use a regimen called multiple daily injections (MDI) or an insulin pump. Both approaches aim to replicate the pancreas by combining a long-acting insulin for background coverage with rapid-acting doses at each meal. Current guidelines recommend that roughly 30 to 50 percent of a person’s total daily insulin comes from the basal component, with the remainder covering meals.
For type 2 diabetes, insulin therapy often starts with a single daily injection of long-acting insulin, sometimes added on top of oral medications. If blood sugar remains uncontrolled, mealtime doses may be added over time. The progression is usually gradual, tailored to how a person’s blood sugar responds.
How Delivery Has Changed
When insulin was first used in the 1920s, patients injected themselves with large glass syringes and reusable metal needles that had to be sterilized by boiling after each use. For over 50 years, the vial-and-syringe method was the only option available for routine home use.
The first manufactured insulin pump appeared in the 1970s. These devices deliver a continuous trickle of rapid-acting insulin through a small catheter placed under the skin, with the user pressing a button to deliver extra insulin at meals. Early pumps were bulky, but modern versions are small enough to clip to a waistband or stick directly to the skin.
The first insulin pen, the NovoPen, arrived in 1985. Pens look like oversized writing pens and use prefilled cartridges with a dial to set the dose. They made injections faster, more discreet, and more accurate than drawing insulin from a vial.
The latest evolution pairs insulin pumps with continuous glucose monitors, creating what are called automated insulin delivery or “closed-loop” systems. A sensor worn on the body reads glucose levels every few minutes and sends that data to the pump, which automatically adjusts the basal insulin rate. These systems don’t eliminate the need for user input at meals, which is why they’re sometimes called “hybrid” closed-loop systems, but they significantly reduce the mental burden of constant decision-making and help smooth out blood sugar swings, especially overnight.
Risks of Insulin Therapy
The most common and most immediate risk of insulin therapy is hypoglycemia, a drop in blood sugar below normal levels. This can happen when a person takes too much insulin, skips a meal, or exercises more than expected. Mild episodes cause shakiness, sweating, and confusion. Severe episodes can lead to seizures or loss of consciousness and require emergency treatment.
Weight gain is another well-known side effect. Insulin promotes the storage of glucose, and when blood sugar that was previously being lost in urine gets redirected into cells, the body retains more calories. Many people gain several pounds in the first months after starting insulin therapy, which can be frustrating but is generally manageable with dietary adjustments.
Injection-site reactions, including small lumps of fatty tissue that form under the skin from repeated injections in the same spot, are common with long-term use. Rotating injection sites helps prevent this. Allergic reactions, once a significant problem with animal-derived insulins, are now rare with modern synthetic formulations.
Once-Weekly Insulin
A newer formulation called insulin icodec is designed to be injected just once a week instead of daily. Clinical trials involving over 4,200 participants with type 2 diabetes found it performed as well as, or better than, daily basal insulin in lowering blood sugar, with similar rates of serious low blood sugar episodes. In people with type 1 diabetes, however, trials showed higher rates of hypoglycemia compared to daily options. For many people with type 2 diabetes who struggle with daily injections, a once-weekly shot could simplify treatment considerably.