Researchers voiced concern on Wednesday about poor quality studies on the popular ADHD treatment Ritalin, saying evidence of some benefits, but also of sleep problems and appetite loss, suggests the drug should be prescribed with caution.

Ritalin is sold by Swiss pharmaceutical firm Novartis NOVN.VX, known generically as methylphenidate and also sold under the brand names Concerta, Medikinet and Equasym. It has been used to treat Attention Deficit Hyperactivity Disorder (ADHD)for more than 50 years.

The Cochrane Review researchers, who conducted a full assessment of studies on the benefits and harms of the Attention Deficit Hyperactivity Disorder (ADHD) drug, said evidence on its use in children was poor.

"Our expectations of this treatment are probably greater than they should be," said Morris Zwi, a London-based consultant child and adolescent psychiatrist, who worked on the review.

"Whilst our review shows some evidence of benefit, we should bear in mind that this finding was based on very low-quality evidence. What we still need are large, well-conducted trials to clarify the risks versus the benefits."

Cochrane Reviews are conducted by international panels of independent researchers and considered as studies of the best available science on a topic.

Jonathan Green, a professor of child and adolescent psychiatry at Britain's Manchester University who was asked to comment on the Cochrane Review, said it would be "wrong to draw the conclusion ... that methylphenidate is ineffective.

"In fact, clinical level evidence strongly supports the effectiveness of methylphenidate for many children with ADHD."

The Cochrane Review included data from 185 randomized controlled trials involving more than 12,000 children or adolescents. The studies were conducted mainly in the United States, Canada and Europe, and each one compared Ritalin with either a placebo dummy pill or no intervention.

ADHD is one of the most commonly diagnosed childhood disorders and can continue through adolescence into adulthood.

Symptoms include difficulty focusing, impulsive behavior, and extreme hyperactivity. It is estimated to affect about 5 percent of children.

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In their review, the Cochrane researchers found that Ritalin led to modest improvements in ADHD symptoms, general behavior, and quality of life, but that side-effects included a higher risk of sleep problems and loss of appetite.

The researchers added, however, that their confidence in the evidence was low since many of the trials were not conducted with sufficient rigor and results reporting was not complete.

"Clinicians prescribing methylphenidate must take account of the poor quality of the evidence, monitor treatment carefully, and weigh up the benefits and adverse effects," they said.