Sales of Epidiolex, the only cannabis drug approved for sale in the US, netted its owner $US116.1m ($180.7m) in sales in the March quarter, proving how lucrative a registered drug can be for marijuana companies.

“In the first quarter of 2020, we have seen continued strength of the Epidiolex brand in both the US and Europe and remain confident about prospects for growth in the remainder of the year,” GW chief Justin Gover said.

The drug has been launched in the US, the UK and Germany, and GW Pharma is looking to introduce it in France, Spain and Italy this year, notwithstanding delays caused by the COVID-19 pandemic.

Medlab Clinical (ASX:MDC) is one Australian company looking to register a cannabis drug, NanaBis, which it is testing for efficacy in treating cancer pain.

Europe is seen as a key medical cannabis market, as the key EU countries have legalised the medical use of marijuana. Germany allows cannabis to be covered by insurers, unlike Australia, which makes that state particularly attractive.

The US Food and Drug Administration (FDA) approved Epidiolex, made by NASDAQ-listed GW Pharma, for two forms of childhood epilepsy in 2018.

In Australia the only cannabis drug approved for sale is nabiximols, which is marketed as Sativex, a treatment for spasticity due to multiple sclerosis.

Nabilone and dronabinol also fall into the cannabis classification but use synthetic rather than natural forms of the active ingredients in marjiuana. Both were approved in 1985 but haven’t gained significant traction in the market.

Evaluate Pharma forecast Epidiolex to see $US1bn in sales by 2024. It forecast sales of $US67m for dronabinol and $35m for nabiximols in 2021.

Few cannabis drugs have secured pharmaceutical registration from regulators around the world for a number of reasons.

Claims around marijuana’s health properties haven’t been backed by clinical trials, which are required by regulators as proof a drug works and is safe.

And marijuana presents a specific problem in that plant extracts do not just contain THC or cannabidiol, the current two main compounds drug companies are seeking to use, but tens of other compounds as well.

Under normal circumstances a company would have to trial a drug using a plant extract a number of different times to ensure that the inclusion or removal of a compound doesn’t change the way a drug works, or that a single minor compound doesn’t interact with other drugs negatively.

The FDA has introduced a botanical route to registration for drugs that contain other vegetable matter as ingredients, but experts say the testing required under this pathway for a drug is still onerous.