An inhaled drug commonly used to treat children with asthma cuts about half an inch off their height permanently, researchers reported on Monday.

But the good news is that the stunting effect doesn’t get worse over time, the researchers report in the New England Journal of Medicine. They said doctors can work with parents to reduce the dose of the drug as much as possible to minimize the effects.

The drug is called budesonide and is marketed under several brand names, including Rhinocort and Pulmicort. It is very effective at controlling serious asthma, which affects an estimated 6 million U.S. children and millions more adults. So the researchers don’t recommend taking kids off the drug if they need it.

A big study done more than a decade ago showed the drug was safe and very effective but doctors noted at the time that the kids in the study were about half an inch shorter if they got budesonide instead of other asthma treatments. The new study, presented at the European Respiratory Society Annual Congress in Vienna, Austria, shows the effect may be permanent.

“This was surprising because in previous studies, we found that the slower growth would be temporary, not affecting adult height,” said Dr. Robert Strunk of Washington University in St. Louis, who worked on the study.

“It clarifies that they do not eventually catch up as they age or fall further behind their peers,” added Dr. Gary Gibbons, director of the National Heart, Lung and Blood Institute.

The original study included more than 1,000 children aged 5 to 12 who got either budesonide, a non-steroid drug called nedocromil, or a placebo or sham treatment. William Kelly of the University of New Mexico and colleagues tracked down 943 of the original children, now adults. The children who got budesonide were still, on average, just about half an inch shorter.

In the original study, kids got a dose of 400 micrograms. Studies since have shown doctors can cut this dose in half and still control asthma, although kids who get even this lower dose are still just under half an inch shorter than children getting different treatments.

“This suggests that finding the minimum dose required to control each child’s asthma could help mitigate any potential effects on height,” Kelly said in a statement.

“If a child is not growing as they should, we may reduce their steroid dose,” agreed Strunk. “But we think that the half-inch of lowered adult height must be balanced against the well-established benefit of inhaled corticosteroids in controlling persistent asthma. We will use the lowest effective dose to control symptoms to minimize concerns about effects on adult height.”