WASHINGTON (CNNMoney.com) - The use of antidepressants appears to increase the onset of diabetes in some high-risk individuals, according to a government-funded study announced Saturday.

Overweight people with high blood-sugar levels and other "pre-diabetic" factors, but who were not taking the anti-diabetic treatment metformin, were two to three times as likely to become diabetic if they were taking antidepressants, according to investigator Dr. Richard Rubin of Johns Hopkins University.

Rubin said the study used all types of antidepressants and did not single out any specific drugs or drugmakers.

"All antidepressants seem to have the same effect," said Rubin, who said that people should not stop taking their antidepressants until researchers could learn more. "We have to find out what was actually going on. We don't want people to go off their medication; we want people to stay on their medication."

Rubin also said the results were not the focus of the test and emerged by accident among the placebo patients who were not taking metformin, but who were taking antidepressants. The diabetes was type 2, which is the most common.

"We didn't set out to study this in particular; this is just what we found," said Rubin, who made the announcement at the American Diabetes Association's annual conference.

Of the 3,187 participants in the test, 5.7 percent were taking antidepressants at the beginning of the trials and 13.6 percent were taking them at the end, said Rubin. The test, which continued for more than three years, is part of $200 million study funded by primarily by the National Institutes of Health.

Wyeth (Research)'s Effexor XR is the leader of the antidepressant industry, with $3.5 billion in 2005 sales. Pfizer (Research)'s Zoloft is no. 2, with $3.3 billion in 2005 sales, but it's losing patent protection in late June, which is expected to trigger a huge plunge in price and revenue. GlaxoSmithKline's antidepressants Wellbutrin, with $1.4 billion in 2005 sales, and Paxil, with $1.1 billion, also are also pressured by generic competition.

Other antidepressants, with sales from last year, include Forest Laboratories (Research)' Lexapro, at $1.9 billion, andEli Lilly & Co. (Research)'s Cymbalta, at $680 million.

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Also from the American Diabetes Association conference:

Pfizer: Inhalable insulin effective

Easier-to-use diabetes drug passes test

New salvo in cholesterol drug war