On average, children on steroids for asthma were half an inch shorter than their peers.
It is the first major study to follow children with asthma into adulthood for height checks, even though many parents have long held concerns about steroids potentially affecting their growth.
But they should be reassured that steroids can be lifesaving and untreated asthma can also lead to poor growth, according to doctors.
The study findings were presented yesterday at the European Respiratory Society meeting in Vienna, Austria, and published online in the New England Journal of Medicine.
It involved more than 1,000 children aged 5-12 who were treated for mild to moderate asthma for four years as part of a U.S. clinical trial.
The children were divided into three groups: one received twice-daily budesonide, an inhaled corticosteroid medication; a second group received nedocromil, an inhaled non-steroid medication; and a third group received a placebo.
All children received albuterol, a fast-acting drug also known as salbutamol for relief of acute asthma symptoms, and oral corticosteroids as needed for asthma symptoms.
The researchers followed 943 participants in the trial at regular intervals until they reached adult height at 18 for girls and 20 or older for men.
The average adult height was about one-half inch, or 1.2cm, shorter in the group that received budesonide than in those taking nedocromil or placebo.
The patients who had slower growth were primarily between 5-11 years old when they began using budesonide.
The slower growth took place only in the first two years of the four-year study.
As the study progressed, the children who took the budesonide remained one-half inch shorter through adulthood than the children who did not use the drug.
Study leader Robert Strunk, the Donald Strominger Professor of Pediatrics at Washington University School of Medicine in St Louis, said 'This was surprising because in previous studies, we found that the slower growth would be temporary, not affecting adult height.
'But none of those studies followed patients from the time they entered the study until they had reached adult height.'
The researchers considered other factors that might have affected growth, including gender, age at the time the child entered the trial, how long the child had had asthma, as well as ethnicity, severity of asthma and reactivity to a skin test for allergies.
Prof Strunk said 'We found it made no difference if they were boys or girls or how long they had had asthma.
'We also looked at the height of the parents, and that didn't have any impact, either.'
Prof Strunk said physicians monitor the progress of children with asthma to check for side effects from steroids.
He said 'If a child is not growing as they should, we may reduce their steroid dose.
'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 minimise concerns about effects on adult height.'
Inhaled corticosteroids are the most effective form of anti-inflammatory treatment for asthma, which affects one in seven children in Britain.
Malayka Rahman, research analysis and communications officer at Asthma UK, says: 'We know that some people with asthma don't always take their medicines as prescribed because they are concerned about the side effects of their medication.
'Inhaled corticosteroids are highly effective in the treatment of asthma and can save lives. So it is crucial to remember the benefits of taking inhaled steroids and these often far outweigh the costs.
'It is important to note that chronic untreated asthma in children can itself cause poor growth. If parents are concerned about any aspect of their child's medication they should talk to their doctor or asthma nurse.'
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