A $450 million project to build one of the world's largest medicinal cannabis glasshouses in Queensland has been approved by the federal government.

The federal government has approved a giant medicinal cannabis glasshouse project in Queensland it predicts will funnel jobs and a billion dollars into the economy.

Canadian company Asterion Cannabis has been granted approval to build the facility in Toowoomba, capable of producing up to 20,000 plants for harvest per day.

Science Minister Karen Andrews says the fully-automated glasshouse, one of the largest in the world, will produce 500 tonnes of medicinal cannabis each year, with an export value of $1 billion.

"The $450 million project will boost jobs across the Toowoomba region, and help position Australia as a major exporter of medicinal cannabis," she said.

Asterion has also signed a research contract with the University of Queensland for an 18 months program to investigate cloning more productive strains of cannabis to meet growing demand.

The drug is used to treat conditions including epilepsy, arthritis, multiple sclerosis, severe nausea and chronic pain.

The new build comes as Queensland on Thursday scrapped a rule requiring patients to obtain state approval to receive the drug.

People consulting with a specialist doctor can now be directly prescribed medicinal cannabis, although general practitioners will still need to apply to Queensland Health and the Therapeutic Goods Administration.

It remains illegal for the public to grow cannabis for medical purposes.