An eight-year-old girl who endures 400 daily epileptic seizures will become Mexico's first authorized consumer of medical cannabis after the government granted her an exemption to its marijuana ban.

The health ministry announced in a statement that it would facilitate the paperwork needed to import a cannabis oil that is believed to alleviate epileptic fits.

"We are happy," Raul Elizalde, the girl's father, told AFP by telephone after he met with the head of Cofepris, the health agency that oversees medicine imports. "It's our last hope."

"We want to reduce the number of convulsions from 400 per day to none. We hope that she could become more independent, that she could walk and speak and eat on her own," he said.

Grace, who lives in the northern industrial hub of Monterrey, has a severe form of epilepsy known as the Lennox-Gastaut syndrome.

Her parents have tried a slew of treatments, including brain surgery, to ease their daughter's pain, but nothing has worked and her condition has worsened.

Last month, a judge gave her desperate parents permission to get cannabidiol (CBD) despite government objections in a country engulfed in a bloody drug war.

Elizalde said the doctor must now write a prescription and they would then seek to import the drug from the United States or Norway.

The health ministry said it would let Grace, as her parents call her, import Epidiolex, a drug produced by Britain's GW Pharmaceuticals that is still in the investigative phase of development.

"It must be clarified that this health authorization does not give the green light to import marijuana in any of its forms," the health ministry said in a statement.

Elizalde said that while the ministry gave them an exemption, the court battle continues as the government has filed a petition to overturn the judge's decision.