Parents are being warned not to give Tamiflu to children with swine flu because the risks far outweigh the negligible benefits.

Scientists said the powerful anti-viral puts children at higher risk of dangerous complications but has little impact on the length of their illness.

The study for a respected medical journal is the most extensive research of its kind yet carried out. It concluded Tamiflu also has very little impact on the spread of swine flu, and handing it out freely could actually increase the virus's resistance to the drug.

The research comes on the heels of a study which found half the children taking Tamiflu had side-effects such as vomiting, nausea and nightmares. The two experts behind the study, Dr. Carl Heneghan, a GP from the John Radcliffe Hospital in Oxford, and Dr. Matthew Thompson, a GP and researcher at Oxford University, analyzed four studies of children aged one to 12 taking Tamiflu or another anti-viral, Relenza.

It found that these children were likely to get better less than a day earlier than they would with just rest and recuperation, while in two of the studies the benefit was not statistically significant.

Dr Heneghan said of Tamiflu: 'The downside of the harms [which can include vomiting and dehydration] outweigh the one-day reduction in symptomatic benefits.' Dr Thompson said otherwise healthy children with mild symptoms should be treated with rest and drinks to cool high temperatures but parents should be on their guard for any signs that their child is getting worse.