Nearly all insulin used today is synthetic. Since 1982, the vast majority of insulin prescribed worldwide has been produced using genetically engineered bacteria or yeast rather than extracted from animal organs. The FDA approved the first biosynthetic human insulin, Humulin, on October 28, 1982, making it the first medical product of any kind created through recombinant DNA technology.
That said, the word “synthetic” can mean different things depending on what you’re really asking. Insulin isn’t assembled molecule by molecule in a chemistry lab. Instead, living organisms are programmed to grow it. And a small amount of animal-derived insulin is still available in certain countries. Here’s how it all works.
How Synthetic Insulin Is Made
Modern insulin production starts with the human gene for insulin. Scientists insert that gene into the DNA of a microorganism, typically E. coli bacteria or a type of yeast. These modified organisms are then grown in large fermentation tanks, where they produce insulin protein the same way they’d produce any of their own proteins. The insulin is harvested, purified, and processed into the injectable form people use.
The result is structurally identical to the insulin your pancreas would make on its own. That’s why it’s formally called “biosynthetic human insulin,” a term that captures both parts: it’s biologically grown, but through an engineered process. The manufacturing has gotten more efficient over the decades. Newer production methods have eliminated some of the most expensive and time-consuming steps, like recovering proteins from bacterial waste and using costly enzymes to trim the insulin molecule into its final shape.
Human Insulin vs. Insulin Analogs
There’s an important distinction between two categories of synthetic insulin. “Human insulin” is an exact copy of what the human body produces. It works, but it doesn’t perfectly mimic the body’s natural insulin release patterns, which spike quickly after meals and maintain a low baseline the rest of the time.
To solve that problem, pharmaceutical companies developed insulin analogs. These start with the human insulin molecule but have small, deliberate changes to a few amino acids (the building blocks of the protein). For example, one long-acting analog has two extra amino acids added to one chain and one amino acid swapped on another. These tiny modifications change how the insulin dissolves under the skin, which controls how fast it enters the bloodstream and how long it lasts.
This is why your pharmacy carries so many different insulin products. They fall along a spectrum of speed:
- Rapid-acting: starts working in about 15 minutes, peaks at 1 hour, lasts 2 to 4 hours
- 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
- Ultra-long-acting: starts in about 6 hours, has no peak, lasts 36 hours or longer
All of these are synthetic. The rapid-acting and long-acting versions are analogs with modified amino acid sequences. Regular and intermediate-acting versions can be either exact copies of human insulin or analogs, depending on the brand.
Is Animal Insulin Still Available?
Before 1982, all insulin came from the pancreases of pigs and cattle, harvested during meat processing. This animal-sourced insulin kept people with diabetes alive for decades, but it carried drawbacks. Beef insulin in particular triggered higher levels of antibody formation, meaning the immune system would partially fight the insulin as a foreign substance. Pork insulin was closer to human insulin in structure and caused fewer immune reactions, though the clinical significance of those antibodies was never fully settled.
Animal insulin hasn’t disappeared entirely. In the UK, one manufacturer (Wockhardt) still supplies both pork and beef insulin under the Hypurin brand, available in short-acting, intermediate-acting, and long-acting formulations. Some people who’ve used animal insulin for years prefer to stay on it, and it can be imported for personal use in countries where it isn’t directly sold. But it’s a niche product now. The major manufacturers, Eli Lilly, Novo Nordisk, and Sanofi, all produce exclusively biosynthetic insulin.
Why the Switch From Animal to Synthetic
The shift happened for several practical reasons. Supply was one: harvesting enough pig and cow pancreases to meet global demand was increasingly difficult as diabetes rates climbed. Consistency was another. Biosynthetic insulin can be produced in precisely controlled conditions, batch after batch, with purity standards enforced by pharmacopeia guidelines that limit contaminants to trace amounts.
The immunogenicity question, whether synthetic insulin causes fewer immune reactions, turned out to be less dramatic than initially hoped. A large Cochrane review of clinical trials found that antibody levels did tend to drop when people switched from animal to human insulin, but the difference often leveled out after six months and rarely reached statistical significance, except when switching specifically from beef insulin. Allergic reactions at injection sites had already been declining through the 1970s as purification techniques improved for all insulin types, animal and synthetic alike.
The real advantages of biosynthetic production were scalability and the ability to engineer analogs. Once you’re building insulin from a gene, you can tweak that gene to create faster or slower-acting versions. That flexibility simply wasn’t possible with animal-sourced insulin.
What’s Next for Synthetic Insulin
Researchers are working on what’s sometimes called “smart insulin,” a synthetic protein designed to respond automatically to blood sugar levels. One approach being developed at Indiana University School of Medicine combines the functions of insulin and its counterpart hormone, glucagon, into a single fusion protein. It works by exploiting the liver’s natural ability to respond differently depending on whether blood sugar is too high or too low: when glucose is elevated, the insulin effect dominates; when it drops, the glucagon effect takes over.
The goal is two versions: a once-weekly injection and a short-acting form for insulin pumps. This could reduce one of the most dangerous aspects of insulin therapy, the risk of blood sugar dropping too low. The research is still early, with many steps remaining before it could reach patients, but it represents the direction synthetic insulin is heading: not just replacing what the body makes, but improving on it.