A liquefied form of medical marijuana being studied in Manhattan holds promise for the treatment of rare and devastating forms of epilepsy that have failed other therapies, medical investigators say.

Doctors at New York University Langone Comprehensive Epilepsy Center say the medication cannabidiol effectively treated patients with Dravet syndrome and Lennox-Gastaut syndrome as well as nearly a dozen other rare forms of the disease.

Both Dravet and Lennox-Gastaut syndromes can cause severe intellectual impairment and physical disabilities, said Dr. Scott Stevens of North Shore University Hospital in Manhasset, who was not involved with the research.

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Lead investigator Dr. Orrin Devinsky says his findings are preliminary and more comprehensive research is required before this form of medical marijuana can be widely prescribed.

"There have been few formal studies of this marijuana extract," Devinsky said of the orally-administered liquid, which already has received orphan drug status in the United States for children with Dravet syndrome. An orphan drug is any medication approved for rare, recalcitrant conditions.

Cannabidiol is sold under the brand name Epidiolex; the psychoactive chemical component of the drug -- the portion that creates a marijuana high -- has been removed. The drug, nevertheless, is considered highly potent and generates powerful activity in the brain.

There have been, however, paltry few formal studies of the extract, Devinsky said.

He is expected to report results of the research Saturday at the American Academy of Neurology's 67th annual meeting in Washington, D.C.

More than 200 people who ranged from toddlers to adults, all stricken with one of the devastating seizure syndromes, were given the medication to determine how well it controlled their epilepsy.

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The number of seizures for patients with Dravet syndrome decreased by 53 percent. For those with Lennox-Gastaut syndrome, seizures declined by 55 percent. Side effects were reported in more than 10 percent of patients, who stopped taking the drug because of drowsiness, diarrhea, decreased appetite and fatigue.

Stevens, director of the Advanced Clinical Experience program in Neurology at North Shore, said the results were promising but he noted that he would rather see a randomized, double-blind placebo-controlled study of cannabidiol to determine its genuine effectiveness. Such a study is considered the gold standard of scientific investigation and eliminates potential for a "placebo effect," a sense of benefit when in reality there was none.

"More research is still needed because the study was 'open-label.' Patients knew what they were receiving," Stevens said.

"When studies are open-label the results may not tell us the whole picture. Patients should not know what they receiving to avoid a placebo effect," he said.

Devinsky's investigation of liquid marijuana is the largest to date, Stevens said, adding that he would not recommend the medication to his patients based solely on this research.

"What I want is a good evidence-based answer for my patients," Stevens said yesterday. "If a patient asked me [about the drug] I would have to say 'We don't know about all of the side effects.'

"I do think it has promise and hopefully in the near future we will know all of the side effects for treatment of severe epilepsy syndromes," Stevens said.