There are four main types of diabetes: type 1, type 2, gestational diabetes, and monogenic diabetes. But the full picture is more nuanced than that. Several additional forms, including a slow-onset autoimmune version often misdiagnosed as type 2 and diabetes triggered by other medical conditions or medications, bring the real count higher. Around 40 million people in the U.S. alone live with some form of diabetes, representing about 12% of the population.
Type 1 Diabetes
Type 1 diabetes is an autoimmune disease. Your immune system mistakenly attacks the insulin-producing cells in your pancreas, eventually destroying them entirely. Without those cells, your body cannot make insulin at all, and you need to take insulin from the time of diagnosis for the rest of your life.
Symptoms often appear in childhood, sometimes as young as age 4 to 6, though it can develop at any age. Type 1 accounts for roughly 5% to 10% of all diabetes cases. Because it involves a complete loss of insulin production rather than a gradual decline, blood sugar can spike dangerously fast if insulin isn’t replaced.
Type 2 Diabetes
Type 2 is by far the most common form, making up about 90% to 95% of all cases. Unlike type 1, your pancreas still produces insulin, at least initially. The problem is that your muscle, liver, and fat cells stop responding to it properly, a condition called insulin resistance. Your pancreas tries to compensate by making more insulin, but over time it can’t keep up. Eventually, it may produce less and less insulin, or stop producing it altogether.
Type 2 is more common in adults, but rates among children and teenagers have been rising. Risk factors include excess weight, physical inactivity, and family history. Many people with type 2 diabetes manage the condition with lifestyle changes and oral medications, though some eventually need insulin as the disease progresses.
Gestational Diabetes
Gestational diabetes develops during pregnancy in someone who didn’t have diabetes before. It affects 5% to 9% of U.S. pregnancies each year. Hormones produced by the placenta can make your cells more resistant to insulin, and if your pancreas can’t produce enough extra insulin to overcome that resistance, blood sugar rises.
Testing typically happens between 24 and 28 weeks of pregnancy. Gestational diabetes usually resolves after delivery, but it significantly raises the risk of developing type 2 diabetes later in life for both the mother and child.
LADA: The “In-Between” Type
Latent autoimmune diabetes in adults, or LADA, is sometimes called type 1.5 because it shares features of both major types. Like type 1, it’s caused by an autoimmune attack on the pancreas. But unlike type 1, that attack happens slowly. People with LADA still produce some insulin at first, so they typically don’t need insulin injections right away.
Symptoms usually start after age 30, which is older than the typical onset for type 1. Because the pancreas is still partially functional at diagnosis, many people with LADA are initially told they have type 2 diabetes. A clue that it might be LADA instead: the person is lean, physically active, or losing weight without trying, which doesn’t fit the usual type 2 profile. Over months or years, insulin production drops and insulin therapy becomes necessary.
Monogenic Diabetes
Monogenic diabetes is caused by a change in a single gene, unlike type 1 and type 2, which involve complex interactions between multiple genes and environmental factors. Researchers have identified variants in more than 20 genes that can cause it. The two main forms are maturity-onset diabetes of the young (MODY) and neonatal diabetes.
MODY is typically inherited from one or both parents and often appears in adolescence or early adulthood. It can look a lot like type 1 or type 2, which means it’s frequently misdiagnosed. Neonatal diabetes shows up in the first six months of life and is usually caused by a gene change that happened while the baby was developing in the womb, not something inherited from the parents.
These gene variants cause problems in different ways. Some prevent the pancreas from developing correctly. Others cause it to produce insulin that doesn’t work well, or they destroy the cells that make insulin. Getting the right diagnosis matters because some forms of monogenic diabetes respond to specific treatments that differ from the standard type 1 or type 2 approach.
Secondary Diabetes
Secondary diabetes develops as a side effect of another medical condition or a medication. Diseases that damage the pancreas, like chronic pancreatitis or cystic fibrosis, can impair insulin production directly. Hormonal conditions that increase insulin resistance can also push blood sugar into the diabetic range.
A surprisingly long list of medications can trigger or worsen diabetes as well. Steroids like prednisolone are among the most common culprits. They cause dose-dependent insulin resistance, meaning the higher the dose, the worse the effect. Certain antipsychotic medications, particularly clozapine and olanzapine, have been linked to new-onset diabetes. Anti-rejection drugs given after organ transplants cause diabetes in up to 28% of recipients taking certain regimens. Even some blood pressure medications, like thiazide diuretics and certain beta-blockers, carry a modest increase in risk.
In many of these cases, diabetes improves or resolves if the underlying condition is treated or the medication is changed. But that’s not always possible, especially when the triggering medication is essential.
Prediabetes: Not a Type, but Worth Knowing
Prediabetes isn’t a separate type of diabetes, but it’s the stage right before type 2. Your blood sugar is higher than normal but not high enough to qualify as diabetes. The diagnostic ranges are an A1C between 5.7% and 6.4%, or a fasting blood sugar of 100 to 125 mg/dL.
An estimated 115 million U.S. adults have prediabetes. Without changes, many will progress to type 2 diabetes within a few years. The encouraging part is that prediabetes is often reversible with weight loss, increased physical activity, and dietary changes.
Why the Exact Count Depends on How You Count
If you count the broad, well-established categories, there are four main types: type 1, type 2, gestational, and monogenic. Add LADA and secondary diabetes and you’re at six. Factor in that monogenic diabetes alone encompasses more than 20 genetically distinct subtypes, and the number climbs further. Some researchers have proposed reclassifying diabetes into five or more clusters based on biology rather than the traditional labels, though that framework hasn’t replaced the current system.
For most practical purposes, the distinction that matters most is understanding which type you or someone you know is dealing with, because the cause, progression, and treatment differ substantially between them. A person with MODY may do well on a low-dose oral medication. Someone with type 1 needs insulin from day one. A person with steroid-induced diabetes may see their blood sugar normalize once the medication is stopped. Getting the specific diagnosis right is what makes effective treatment possible.