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What Plants Have THC in Them?

Delta-9-Tetrahydrocannabinol (THC) is a type of ​phytocannabinoid​, a chemical compound produced by plants. THC is famous for its psychoactive effects on humans and other animals when ingested in the right quantities. Plants that contain THC include cannabis (​Cannabis sativa​) and, at low levels, hemp (​Cannabis sativa​ ssp. ​sativa​).

Plants That Contain THC

Cannabis and hemp are the primary plants that contain THC. However, the percentage they contain varies between strains. Horticulturists growing cannabis can cross strains to produce new varieties. The percentage of THC on a dry-weight basis in cannabis varies from 3 percent up to 30 percent. However, 30 percent is considered very high THC content. Many commercially available cannabis strains, where legal, contain up to 20 percent THC.

Hemp and cannabis are very closely related. Industrial hemp strains contain no more than 0.3 percent of THC on a dry-weight basis. This level of THC is so low that hemp is considered non-psychoactive. In addition to THC, hemp and cannabis contain more than 60 other types of cannabinoids.

THC in Leaves and Flowers

Glandular trichomes​ are structures on plants that secrete various chemical substances for protection. In cannabis plants, the trichomes secrete THC and other cannabinoids. Cannabis plants have two main types of glandular trichomes: stalked and sessile. These trichomes look like a balloon structure on the end of a stick.

Cannabis is a ​dioecious​ plant species, meaning that there are separate male plants and female plants. It is the female flowers, called ​buds​, that have the highest concentration of trichomes. The leaves on female plants, the entire male plant and hemp are also covered in glandular trichomes but in very low numbers. Roots do not have glandular trichomes, and therefore contain no THC.

Phytocannabinoid Roles

There are many different types of phytocannabinoids that different plants produce. Phytocannabinoids are defined by their type of chemical structure known as ​bioactive meroterpenoids​. Cannabis was the first plant that was discovered to contain phytocannabinoids, but since then, cannabinoids and cannabinoid-like chemicals have been found in several other plants and fungi.

Currently, the roles cannabinoids play across plant species is poorly understood. It is thought that cannabis uses its cannabinoids like sunscreen and for protection against herbivores.

Under high temperatures or when the plant is bitten by a herbivore, the glandular trichomes burst. The sticky, noxious contents spill over the plant’s surface, trapping insect herbivores and protecting the surface of the plant from UV-B rays. Cannabis produces more cannabinoids when exposed to higher temperatures and fewer when soil mineral content is low.


Lepidote rhododendron species, native throughout Asia, have glandular scales on their leaves. These glands contain bioactive monoterpenoids with a cannabinoid-like backbone. It is thought that the phytocannabinoids in rhododendrons are used to deter insects.


Liverworts are a group of simple plants, similar to moss because of their lack of vascular tissue. One type of liverwort from the genus ​Radula​ is primarily found in New Zealand. Some liverwort species, including ​Radula perrottetii,​ produce a psychoactive cannabinoid-like compound similar to THC termed ​perrottetinene​. Researchers are highly interested in perrottetinene for its anti-inflammatory potentials.

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While the exact purpose of perrottetinene is unclear, in general liverworts are rarely damaged by insects, small mammals, fungi or bacteria. Liverworts have specialized cells called oil-bodies that contain terpenoids and aromatic oils. The bitter-tasting contents of these oil bodies produce strong smells and a range of bioactivities. These oil bodies are unique to liverworts in the Bryophyta division.

Cannabinoids in Humans and Animals

Cannabinoid compounds are not unique to plants. Humans and many other animals internally produce endocannabinoids involved in central nervous system development and lipid signaling networks. When humans and other animals ingest plants with cannabinoids, they can produce various therapeutic effects because they interact with cannabinoid receptors in the body.

Unlike THC, consuming other cannabinoids does not produce psychoactive effects. Studies exploring the medicinal benefits of consuming plant-based and synthetic cannabinoids are on the rise. Early studies show they may help minimize nauseous effects in chemotherapy patients, reduce certain symptoms in people with multiple sclerosis and help manage chronic pain.

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  • National Academies Press: Therapeutic Effects of Cannabis and Cannabinoids
  • British Journal of Pharmacology: Phytocannabinoids Beyond the Cannabis Plant – Do They Exist?
  • Biological Psychiatry: An Introduction to the Endogenous Cannabinoid System
  • Trends in Plant Science: Phytocannabinoids: Origins and Biosynthesis
  • Cibdol: Other Plants Containing Cannabinoids
  • Scientific American: Lowly Moss-Like Plant Seems to Copy Cannabis
  • Plant and Food Research: Liverworts Would Rather Be ‘Red Than Dead’
  • Congressional Research Service: Defining Hemp: A Fact Sheet
  • Way of Leaf: Average THC Strength Over Time: A 50-Year Look at Marijuana Potency

About the Author

Adrianne Elizabeth is a freelance writer and editor. She has a Bachelor of Science in Ecology and Biodiversity, and Marine Biology from Victoria University of Wellington in New Zealand. Driven by her love and fascination with all animals behavior and care, she also gained a Certificate in Captive Wild Animal Management from UNITEC in Auckland, New Zealand, with work experience at Wellington Zoo. Before becoming a freelance writer, Adrianne worked for many years as a Marine Aquaculture Research Technician with Plant & Food Research in New Zealand. Now Adrianne's freelance writing career focuses on helping people achieve happier, healthier lives by using scientifically proven health and wellness techniques. Adrianne is also focused on helping people better understand ecosystem functions, their importance, and how we can each help to look after them.

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Hemp Production – Keeping THC Levels Low

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Estoy de Acuerdo / I agree

Leo Stefanile, Margaret Bloomquist, and Zeke Overbaugh showing differences in root development of two hemp varieties.
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Hemp Production in North Carolina is new and changing rapidly. There is a massive shortage of research-based info regarding the basic agronomic recommendations but we are making progress. Because of the great interest in hemp from our farmers, industry, community leaders, and potential consumers of hemp products I will summarize what I have learned from listening to numerous people working with this crop.

Hemp can be grown for seed, fiber, or flower (oil extracts). In 2018, North Carolina had 6133 licensed acres, 394 licensed growers, and 1.6 million square feet in licensed greenhouse space. The majority of production is focused on growing hemp for flower, primarily the CBD market. CBD, or cannabidiol, is one of over 100 cannabinoids identified in hemp plants. Another cannabinoid is THC, tetrahydrocannabinol, which is the psychoactive ingredient in cannabis that gives a ‘high’ effect. The amount of THC in a cannabis plant determines whether it is hemp or whether it is marijuana. If the THC content is 0.3% or less, it is hemp. If the THC content is greater than 0.3% it is marijuana.

Female hemp flower. Most (but not all) hemp cultivars are dioecious, meaning male and female flowers are found on separate plants. Hemp growers interested in CBD production want female plants. Photo by Debbie Roos. See full article here.

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Licensed growers of hemp in NC are required to contact the North Carolina Department of Agriculture & Consumer Services (NCDA&CS) at the initiation of flowering ([email protected]). Growers must report when plants are flowering and, thus, are ready to be tested for THC. Someone from NCDA&CS will visit the site and sample hemp 3-5 weeks into flowering. They will take the top 3-5 inches of the plant (NCDA&CS is sensitive to the value of biomass and they are working to minimize the total amount of biomass removed) and if you have multiple varieties you will need multiple tests. The grower must pay for all testing ($59 for the first test). If the level of THC is above 0.3% you will have two options – destroy your crop or pay for a re-test of the THC ($149 for the re-test).

Growers need to be aware that plant stresses (drought, flooding, excessive nutrients, not enough nutrients, heat, cold, etc) can result in THC spikes. According to Paul Adams with theNCDA&CS, in 2017, the NCDA&CS processed 135 hemp samples and 14 came back above 0.3% THC. In 2018 they processed 400 hemp samples and 38 came back above 0.3% THC. About 10% of hemp fields are ‘going hot’ – lingo used to describe a THC spike. This is a serious risk to hemp producers and there is currently no crop insurance to mitigate this risk.

We don’t have solid data on the causes of THC spikes but here are some considerations. While excess nitrogen is often blamed for THC spikes, Dr. Angela Post, NC State University Small Grains Specialist, disagrees with this. In one research trial that Dr. Post conducted, nitrogen was applied at rates of 50, 100, 150, 200, 250, and 300 lbs per acre. While there was no advantage at putting out more than 100 lbs of nitrogen per acre there was no spike in THC. In fact, from just this first year of preliminary data, Dr. Post did not see any relationship between nitrogen and THC or CBD. In fact, Dr. Post wonders if nitrogen deficiencies could result in plant stress, thus causing a THC spike. From just this first year of data the nitrogen recommendation would be 100 lbs of N per acre. However, Dr. Edminsten cautions that this is just one season of data. If he were growing hemp right now he would lean towards a higher nitrogen rate (120 lb/N per acre).

Certainly, variety selection will play a role in THC content of the hemp varieties. We are still gathering information for growers regarding variety performance in NC but there is a listing of how some varieties have performed in Kentucky, including which of those varieties are of concern for THC spikes.

Take a look at this article for more information on prices for hemp floral biomass:

The information regarding hemp is changing quickly so keep visiting these resources and stay tuned.