Researchers published in JAMA Pediatrics found that only two drugs known to help migraine-plagued adults reduced the frequency of children's headaches better than a placebo. Even in those cases the effect was small - a difference of less than one headache per month compared to the dummy pills.

According to data from the Cleveland Clinic, about 2 percent of young children and 7 to 10 percent of older children and teenagers up to age 15 get migraines.

No drugs have been rigorously tested and approved for preventing migraines in children, so doctors have to rely on medicine for adults, experts said.

"All the drugs in our analysis have been found effective in adults with migraine headaches, but few were beneficial among children," wrote study leader Jeffrey Jackson from the medical College of Wisconsin in Milwaukee, and colleagues.

"This suggests there may be something different about pediatric migraines or that the response to treatment differs between children and adults."

In the study, Jackson and his colleagues looked at 21 trials comparing headache drugs to each other or to placebos. They found that only topiramate (marketed as Topamax) and trazodone (Oleptro and Desyrel) significantly reduced the frequency of headaches in children and teens who got regular migraines.

Other adult headache prevention medicines, including flunarizine, propanolol and valproate, were of no help.

"Parents should be aware that our medication choices aren't as good as they should be," said Jennifer Bickel, a neurologist and headache specialist at Children's Mercy Hospitals and Clinics in Kansas City, Missouri, who was not part of the study.

Placebo pills alone led to a drop in children's headache frequency from between five and six headaches per month to three per month, which might have to do with the effect of seeing a doctor and being reassured the pain isn't due to anything serious, Bickel said.

She said there is the least research on the one percent of children who are most severely affected by migraines, those with chronic daily headaches.

For those youth, "we don't have any evidence to suggest that the medications are enough," she said.

According to a report from the U.S. Food and Drug Administration published in the same journal issue, two drugs - almotriptan malate (Axert) and rizatriptan benzoate (Maxalt) - are approved to treat, but not prevent, headaches in children and teens.