What's the Difference Between Hemp and Marijuana?

What's the difference between hemp and pot, anyway? A single genetic switch. In 2011, researchers from the University of Saskatchewan announced that they'd discovered the genetic alteration that allows psychoactive cannabis plants (Cannabis sativa) to give users a high (as compared to industrial hemp plants, which are no fun for smoking).

Industrial hemp plants are the same species as marijuana plants, but they don't produce a substance called tetrahydrocannabinolic acid (THCA). This is the precursor to tetrahydrocannabinol (THC), the psychoactive ingredient in pot. Hemp plants fail to produce this substance because they lack a gene that makes an enzyme to produce THCA, according to University of Saskatchewan biochemist Jon Page.

In contrast, marijuana plants do produce THCA but don't create much of a substance called cannabidiolic acid (CBDA), which occurs in abundance in hemp but competes with THCA for raw materials. Thus, hemp is rich in nonpsychoactive CBDA, while marijuana is chock full of mind-bending THC.

"The transcriptome analysis showed that the THCA synthase gene, an essential enzyme in THCA production, is turned on in marijuana, but switched off in hemp," Page says.

Tim Hughes, co-leader of the project, is a professor at the Terrence Donnelly Centre for Cellular and Biomolecular Research and the Department of Molecular Genetics at the University of Toronto. He explains the team compared the potent Purple Kush marijuana variety with 'Finola' hemp, which is grown for seed production. Hemp lacks THCA, but does contain another, non-psychoactive substance called CBDA, or cannabidiolic acid.

"Detailed analysis of the two genomes suggests that domestication, cultivation, and breeding of marijuana strains has caused the loss of the enzyme (CBDA synthase), which would otherwise compete for the metabolites used as starting material in THCA production," Hughes says.

Essentially, this means that over thousands of years of cultivation, hemp farmers selectively bred Cannabis sativa into two distinct strains - one for fibre and seed, and one for medicine. Marijuana has been used medicinally for more than 2,700 years, and continues to be explored for its pharmaceutical potential.

"Plants continue to be a major source of medicines, both as herbal drugs and as pharmaceutical compounds," Page says. "Although more than 20 plant genomes have been published, ranging from major food crops such as rice and corn, to laboratory models like Arabidopsis, this is the first genome of a medicinal plant."

The researchers expect that sequencing the Cannabis sativa genome will help answer basic questions about the biology of the plant as well as furthering development of its myriad applications.

These include strains for pharmaceutical production, high-producing industrial hemp plants, and hemp seed varieties to produce high-quality edible oil. Hemp seed oil is rich in omega 6, an essential fatty acid, and its fibre is used in the production of textiles.

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