Tens of thousands of asthmatics may be taking dangerous amounts of steroids, research suggests.
Scientists from Amsterdam University looked at more than 2,300 people with the condition.
They found nearly a third (29 per cent) were on high doses of oral steroids, which put them at risk of diabetes and osteoporosis.
Further analysis showed 78 per cent of the patients were not taking their steroid inhalers as prescribed.
With their disease poorly controlled, the scientists worry patients are then forced to rely on risky medication.
Tens of thousands of asthmatics may be taking dangerous amounts of steroids (stock)
'Asthma patients using high doses of oral steroids are at risk of serious adverse effects such as diabetes, osteoporosis and adrenal insufficiency,' lead author Ms Katrien Eger said.
One in 12 adults in the UK are being treated for the common condition, Asthma UK statistics show.
And in the US, one in 13 people suffer, according to the Centers for Disease Control and Prevention.
Many patients rely on steroid inhalers to dampen inflammation in their airways and prevent an asthma attack.
These are considered less harmful than oral versions of the drug because the dose goes directly to the lungs.
However, if symptoms get worse or a patient has an attack, oral steroids may be prescribed.
These help to calm the airways and stop inflammation by blocking the effects of chemicals released by the immune system.
If taken long term, oral steroids have been linked to a higher risk of infection, high blood pressure and weak bones, as well as diabetes.
To better understand how many patients rely on these tablets, the scientists looked at 2,312 asthma sufferers.
'We found 29 per cent of asthma patients who were using high doses of inhaled steroids were also taking harmfully high doses of oral steroids of 420 milligrams (0.01 oz) a year or more,' Ms Katrien Eger said.
The analysis also showed 78 per cent of the patents did not always take their inhaled medication as prescribed or had an incorrect inhaler technique.
The proportion of asthma patients who do not adhere to their inhaler medication or have poor inhaler technique is likely to be similar in other countries, the researchers said.
Asthma is a common but incurable condition which affects the small tubes inside the lungs.
It can cause them to become inflamed, or swollen, which restricts the airways and makes it harder to breathe.
The condition affects people of all ages and often starts in childhood. Symptoms may improve or even go away as children grow older, but can return in