WASHINGTON (CNNMoney.cnn) - Exubera, the first form of inhalable insulin to enter the market, is just as effective for diabetics as injectable insulin, according to a study released Saturday by Pfizer.

Also, Exubera patients gain half as much weight as those injecting insulin, according to the ongoing, late-stage study. Insulin is often blamed for weight gain in diabetics, which is particularly troubling since obesity is one of the prime factors leading to the most common type of diabetes: thus the industry term "diabesity."

Exubera is a handheld inhaler that uses a dry powdered form of insulin, and designed for use by needle-shy diabetics. Approved by the FDA in January, Exubera is expected to enter the U.S. market in mid-July, according to its maker Pfizer (Research), and it is already available in Ireland and Germany. The product can be used by diabetics who have type 2, the most common type of diabetes, and type 1, the rarest and most serious.

The study, released at the American Diabetes Association, is important because even though analyst sales projections range from $1 billion to $2 billion a year, some have doubted Exubera's effectiveness compared to injectable insulin. The more traditional means of taking insulin has been available since the 1920s.

The Pfizer-funded study, led by independent researcher Dr. Julio Rosenstock of the Dallas Diabetes and Endocrine Center, focused on 635 patients with type 2 diabetes and 582 patients with type 1, and showed near-identical blood-sugar level control for those who injected and those who inhaled.

Also, patients with type 2 diabetes on Exubera gained an average of 3.7 pounds, compared to 6.6 pounds for those who injected insulin, according to the study. The type 1 diabetics on Exubera gained an average of 1.7 pounds, compared to 4.4 pounds for those who injected. These results are from the first two years of a five-year test.

Rosenstock, the lead investigator, said the convenience of using Exubera instead of needles "could improve earlier acceptance of insulin" among diabetics.

The FDA based its approval on a different study that focused on safety, according to Pfizer, while this new study focused on efficacy.

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Also from the American Diabetes Conference:

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Easier-to-use diabetes drug passes test