The hand-held device tested in the trial can be used at home
A new hand-held device that delivers a magnetic pulse to the back of the head could become an alternative to drug treatment for people with migraines.
A trial found that 40% of patients were pain free two hours after using the device.
Research showed there were no serious side-effects and patients found the device easy to use at home.
However, doctors say more research is needed to work out the timing of the doses.
Experts from the Albert Einstein College of Medicine in New York carried out the trial to assess the safety and effectiveness of the device.
Previous trials have only involved large, expensive devices which have to be used in a clinic.
The hand-held device emits a single-pulse transcranial magnetic stimulation (sTMS), thought to disrupt the electrical events in the brain which cause the preliminary symptoms of migraines with aura.
Auras are sensory or visual disturbances that occur before a migraine headache sets in.
These include visual symptoms such as spots of light and zigzag lines. Other symptoms include tingling, numbness and difficulties with speaking.
Two hundred patients were asked to use the device to treat migraines with aura over three months. Half of those patients were given placebo treatment.
The findings, to be published in The Lancet Neurology, showed that the real magnetic pulse from the device was significantly more effective than placebo treatment. More patients were pain free two, 24 and 48 hours afterwards.
They affect about 18% of women and 6% of men in the USA and Western Europe
There are two major forms of migraine - with aura and without aura.
Migraine with aura affects about 20-30% of patients
Migraine with aura is characterised by symptoms which usually precede the onset of a headache
Dr Hans-Christoph Diener, from University Hospital Essen in Germany, said: "The use of sTMS could be a major step forward in the treatment of migraine with aura, particularly in patients in whom presently available drug treatment is ineffective."
Wendy Thomas, chief executive of the Migraine Trust, welcomed the new trials but stressed that more research into migraines would be needed before patients could access the treatment.
"We look forward to hearing the results of further sTMS trials in the future.
"Migraine and headache are the least publicly funded of all neurological conditions in the UK, particularly relative to their economic impact," she said.