What is the difference between hemp and marijuana?

Q: What is the difference between hemp and marijuana?

Hemp and marijuana are the same species, Cannabis sativa. The difference is chemistry, breeding and law: hemp is cannabis grown for fibre, seed or low-THC flower, defined in many laws as no more than 0.3% THC by dry weight, while marijuana is drug-type cannabis bred for high THC. The two groups are genetically distinct populations, and many fibre hemps are bred monoecious.

Short answer

Hemp and marijuana are the same species, Cannabis sativa. Hemp is cannabis bred and grown for fibre, seed or low-THC flower, and many laws define it as no more than 0.3% THC by dry weight. Marijuana is drug-type cannabis bred for high THC. Established botany; the legal line varies by place.

Why

One species, two uses. Most botanists treat all cultivated cannabis as Cannabis sativa, with fibre, seed and drug types shaped by thousands of years of human selection ^[3].

The 0.3% line is a convention. Small and Cronquist proposed 0.3% THC in dry flowering tops as a practical boundary between the groups in 1976 ^[1]. Many laws later adopted it, with differences in which THC is counted (THC only, or total THC including THCA) and how samples are taken.

The groups are genetically distinct. Genome-wide markers separated hemp from marijuana as different populations ^[2]. Chemistry differs too: drug types are mostly THC-dominant, many hemps CBD-dominant or low in all cannabinoids ^[4].

Breeding goals differ. Fibre hemp is bred tall, dense-sown and often monoecious, with both sexes on one plant. Drug-type cannabis is grown as seedless (sinsemilla) females for resin.

The numbers

	Hemp	Drug-type cannabis
Species	Cannabis sativa	Cannabis sativa
Legal THC limit (many places)	≤ 0.3% by dry weight	None, or licensed
Bred for	Fibre, grain, oil, CBD	THC-rich resin
Typical chemotype	CBD-dominant or low	THC-dominant
Sex system	Often monoecious (fibre types)	Dioecious; females grown

What to do

Treat "hemp" as a legal and use category, not a separate plant.
Growing hemp? Rules, licences and testing vary; check your local rules.
Growing CBD flower? Test before harvest; CBD-dominant plants still make some THC.
Keep hemp pollen away from a sinsemilla grow.

Common mistakes

Thinking hemp and marijuana are different species.
Assuming "hemp" seed will always test under the limit.
Assuming the 0.3% rule means the same thing everywhere.

Full article: Cannabis plant biology
Answers: THC vs CBD plants · strain vs cultivar
Article: Indica, sativa and ruderalis
Terms: hemp · marijuana · monoecious

Follow-up questions

Where does the 0.3% THC hemp limit come from?

The 0.3% THC line between hemp and drug-type cannabis traces to a 1976 taxonomy by Small and Cronquist, who used 0.3% THC in dry flowering tops as a practical boundary between the two groups. Laws in the US, Canada and the EU later adopted 0.3%, though they differ on which THC counts and how samples are taken. Check your local rules.

Can hemp get you high?

Most fibre and grain hemp has too little THC to produce the effects reported for drug-type cannabis, because it is bred to stay under about 0.3% THC. Some 'hemp' flower is bred high in CBD and close to the legal THC limit, and THC-rich plants can appear in mixed seed. Effects are reported, not promised; legal status depends on testing, not on the name.

Is CBD flower hemp?

CBD flower is usually legally hemp: drug-type-looking buds from CBD-dominant plants kept under the hemp THC limit, often 0.3%. Botanically it is the same species as THC-dominant cannabis, with a different synthase gene. CBD-dominant plants still make a little THC, so a crop can test over the limit, and rules on selling smokable hemp flower vary by place.

Sources

Small E, Cronquist A. 1976. A practical and natural taxonomy for Cannabis. Taxon 25(4):405-435. doi.org/10.2307/1220524

Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. doi.org/10.1371/journal.pone.0133292

Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. doi.org/10.1007/s12229-015-9157-3

Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. doi.org/10.3732/ajb.91.6.966