Insulin use has trebled over the last 20 years in the UK, driven by high rates of obesity-linked type 2 diabetes, according to a new study.
Experts analysed data from patient prescriptions to find a huge increase between 1991 and 2010 in the use of insulin, particularly among people with type 2, which is linked to unhealthy lifestyles.
The number of people using insulin overall trebled from 136,800 in 1991 to 421,300 in 2010.
For those with type 2, the number using insulin rocketed almost eight-fold from 37,000 in 1991 to 277,400 in 2010.
In 1991, more people using insulin had type 1 diabetes than had type 2 diabetes (98,400 versus 37,000), the research also found.
By 2010, this situation had reversed, and 134,900 had type 1 while 277,400 had type 2 diabetes.
The study was published in the Journal of Diabetes, Obesity and Metabolism and was led by a team of academics from Cardiff University and the University of Bristol.
The researchers said the financial cost to the NHS of insulin use increased from £156 million in 2000 to £359 million in 2009.
They blamed more expensive types of insulin but also the huge demand for insulin from people with type 2.
In England alone, the total cost of all medicines used to treat diabetes increased from £573.9 million to £725.1 million between 2005/6 and 2009/10, they added.
Craig Currie, professor of applied pharmacoepidemiology at Cardiff University's School of Medicine, said: "As a result of the study, we found that the number of people injecting insulin in the UK increased three-fold over the 20-year period from 1991 to 2010.
"Also during this period there was more than a seven-fold increase in the number of those with a diagnosis of type 2 diabetes and treated with insulin.
"Most of this is unrelated to clinical need.
"Insulin is very expensive and some of us believe that it involves too many serious side effects in people with type 2 diabetes.
"The increase in the number of people with type 2 diabetes using insulin is a wake-up call for all - not only in terms of lifestyle choices and how we treat people with type 2 diabetes."
But Simon O'Neill, Diabetes UK director for health intelligence, said: "While this study reflects the growing scale of diabetes, it is also important to remember that insulin is an essential treatment that enables people with diabetes to stay alive and effectively manage their condition so that they can reduce their risk of devastating complications such as blindness, amputations and strokes.
"Some people with type 2 diabetes are able to manage the condition with physical activity and healthy eating alone when they are first diagnosed but as the condition is progressive most people will eventually also need to use medications, which can include insulin, to help them effectively manage the condition.
"By making sure that people with diabetes are getting the recommended checks and support they need to manage their diabetes, we can help them avoid complications, which are not only a personal tragedy for all of those involved but are also hugely costly to the NHS."
Around 3.8 million people in the UK have diabetes.
There are three million living with type 1 and type 2 diabetes, and around 850,000 more who have type 2 diabetes but are undiagnosed.