The United States Food and Drug Administration (USFDA) on Monday approved the first marijuana-derived drug to enter the US market – a medication to treat two rare and severe forms of childhood epilepsy.

Epidiolex, made by British biopharma company GW Pharmaceuticals, uses purified cannabidiol (CBD), which is one of more than 80 active compounds in the cannabis plant.

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It contains less than 0.1 percent of tetrahydrocannabinol (THC), the psychoactive component that makes people high.

The drug's effectiveness was studied in clinical trials with 516 patients and when taken with other medications, Epidiolex was shown to be effective in reducing the frequency of seizures when compared with placebo.

'An important medical advance'

USFDA Commissioner Scott Gottlieb said the approval of the drug was "an important medical advance."

"But it's also important to note that this is not an approval of marijuana or all of its components. This is the approval of one specific CBD medication for a specific use," Gottlieb said.

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"And it was based on well-controlled clinical trials evaluating the use of this compound in the treatment of a specific condition," he continued.

Epidiolex is approved to treat Lennox-Gastaut syndrome and Dravet syndrome in patients two years and older, the FDA said. Both forms of epilepsy cause severe seizures.

The approval comes as the cases of a number of children have been highlighted in the UK, where the Home Office has the power to regulate medicine. After considerable public pressure, the Home Secretary used an "exceptional power" to enable a 12-year-old boy to be treated with a batch of a banned drug that had been seized from the boy's mother on her return from Canada to the UK. The six-month supply can be used to treat the boy's seizures, which, without the medication, could number up to 100 a day.

DEA approval needed

Before sales of Epidiolex can begin, the DEA must formally reclassify CBD into a different category of drugs that have federal medical approval.

The DEA sorts chemicals into five categories based on the potential for abuse. Schedule 1 substances such as marijuana and heroin are considered to be the most deadly, and deemed to have no medical benefit at all. The DEA's decision is expected to be made within 90 days.

A total of 30 US states, the District of Columbia, Guam and Puerto Rico allow the use of medical marijuana in some form, according to the US National Conference of State Legislatures.

The approval of Epidiolex comes a week after Canada legalized recreational marijuana use.

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law/jm (AP, AFP, dpa, Reuters)

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