London, Aug 30 (IANS): A drug that is used to help people with sleep disorders stay awake can boost cognitive functions in healthy people, a new study says.

Researchers reviewed 24 studies on the drug modafinil, carried out between 1990 and 2015, and found that it appeared to improve cognitive function, RT.com reported.

Some of the studies also showed gains in flexible thinking, increasing ability to combine information or cope with novelty. The drug didn't seem to influence creativity either way.

However, researchers found that improvement wasn't seen every time, on every test, or for every person. They also found that the studies failed to show any enhancement in the areas of attention, learning and memory.

"What emerged was that the longer and the more complex the task ... the more consistently modafinil showed cognitive benefits," said study co-author Anna-Katharine Brem from Oxford University was reported as saying.

Modafinil, like Adderall and Ritalin, is increasingly being used by college students and adults who don't suffer from ADHD or sleep disorders, but are searching for greater productivity.

The drugs work by increasing the brain's level of dopamine and norepinephrine to boost concentration and alertness.

The drugs can have negative health consequences, though, especially at large doses.

Researchers also found that many of the cognitive tests used in the studies were more appropriate for people with neuropsychiatric illness or neurological disorders.

"The problem with this is that healthy people perform very well in them without taking the drug and so improvements in performance on a substance are harder, if not impossible, to detect," Brem observed.

Researchers said that the studies only gave participants the drug once, so long term claims are hard to make.

Still, they said the benefits of the drug for enhancing attention, executive functions, learning, and memory appear much stronger.

The study was published in the journal European Neuropsychopharmacology.