Gemma Tregent is one of 29 Victorian children trying imported cannabis oil before a locally-made product is available later this year.
The five-year-old suffers at least 40 seizures a day, has restricted mobility and cannot swallow due to severe cerebral palsy and epilepsy.
"She gets agitated, she arm cycles, her back arches, her eyes flick, she gets distressed, her breathing changes, her colour changes," Gemma's mother Ally Tregent told AAP of the symptoms her daughter displays during her seizures.
Gemma's dose of the cannabidoil started on Friday and her mother says she hopes to see improvements in her daughter's symptoms over time.
"It's given us hope. We were at the end of the line with the medications," Ms Tregent said.
The cannabis oil has been fast-tracked from Canada on compassionate grounds for the state's most severely affected children with epilepsy.
Locally-made medicinal cannabis will be available later this year after Victoria in 2016 became the first state to legalise access.
"We've done so because we know for many groups of patients they have been forced to make the very difficult choice about either complying with the law or seeking a treatment that can make life easier," Minister for Health Jill Hennessy told reporters.
Associate Professor Michael Fahey says recent studies suggest medicinal cannabis reduces the frequency of life-threatening seizures.