One in 12 people should be taking a drug to prevent diabetes, researchers estimate.
The drug helps normalise blood glucose levels
More than 8% of the world's population have conditions that greatly increase diabetes risk, and treating these could prevent full-blown disease, they say.
The Lancet study suggests giving a diabetes drug called rosiglitazone to people with impaired glucose regulation would prevent one in seven cases.
Currently, drugs are given if lifestyle changes fail to control blood glucose.
The Canadian researchers from the Population Health Research Institute in Ontario believe earlier intervention with drugs would prevent more cases.
But diabetes experts cautioned there was a danger that offering drugs would send out the wrong message to people - that they could reduce their risk without making lifestyle changes.
And it would cost the NHS money, although it would also potentially save it money by reducing the health complications associated with diabetes.
Type 2, or non-insulin dependent diabetes, develops when people do not make enough insulin, or are unable to make proper use of it.
Without enough insulin, sugar builds up in the bloodstream and causes health problems.
Two conditions that impair glucose regulation - impaired glucose tolerance and impaired fasting glucose - greatly increase the risk of Type 2 diabetes.
The researchers gave 5,269 adults with these conditions either the diabetes drug or a dummy drug daily for three years.
They also stressed the importance of a healthy diet and lifestyle to the participants.
By the end of the study, 280 of the people on rosiglitazone developed diabetes compared with 658 of those who had received the placebo drug, suggesting that the drug, along with basic lifestyle recommendations, reduced the risk of diabetes by about two-thirds.
"For every 1,000 people treated with rosiglitazone for three years, about 144 cases of diabetes will be prevented," said the authors in The Lancet.
This equates to one in seven cases of diabetes prevented.
But the drug can have side effects and cause adverse events, including heart failure, in a small minority.
For every 1,000 treated for three years, the researchers estimate four to five people could develop heart failure who otherwise might not have.
Taking these risks into account, they believe that adding rosiglitazone to basic lifestyle recommendations could prevent substantially more people developing diabetes.
A spokeswoman from Diabetes UK cautioned: "It would be wrong to assume that we can solve the epidemic of Type 2 diabetes by taking a tablet.
"Studies in the US and Finland have shown that small lifestyle changes are effective in delaying or preventing Type 2 diabetes.
"Further research may show that the use of this drug will be of value to certain individuals."
Nicholas Wareham of the Medical Research Council told the Lancet: "The lack of data on long-term benefits and side-effects, and the high cost of therapy, mean that health-care funders are unlikely to see rosiglitazone as an appropriate agent for individuals with impaired glucose regulation."
Rosiglitazone is one of a newer class of oral glucose-lowering drugs available in the UK. It is currently licensed for use in people whose type 2 diabetes is not controlled by lifestyle measures and other diabetes drugs.