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How Do You Determine The THC and CBD Levels of a Plant?

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You will find this question being asked frequently: How do you determine the THC and CBD levels of a plant?

Marijuana potency is a subject of concern for cannabis growers and consumers alike. This represents the phytocannabinoid percentage in a strain or phenotype of cannabis.

A couple of factors will influence the amount of THC or CBD that you expect to find in a strain. The first is of course the genetic makeup of the strain. These characteristics are encoded in the genes and contain information on how much THC or CBD can be produced by the plant. However, the expression of these genetic characteristics are also influenced by environmental factors significantly. That is why you will find a variance in THC or CBD content in spite of cannabis plants sharing a strain. In the next fifteen minutes we shall explore everything there is to know about phytocannabinoid potency including what it is, how to determine it, testing for potency, and finding strains that contain high levels of THC or CBD. To wrap it up, we shall give you a couple of reasons to get you excited about determining the potency of cannabis plants.

What is Marijuana Potency?

Marijuana potency refers to the concentration of cannabinoids in a cannabis plant. Mostly, this represents the amount of tetrahydrocannabinol (THC) or cannabidiol (CBD) which are the two most prominent phytocannabinoids. You may often come across the phrase “a potent strain of weed.” This either signifies a high concentration of THC or CBD. In the traditional sense potency mostly represented the amount of the psychoactive compound THC in a strain of weed. In this sense. Potent strains were associated with overwhelming psychoactive effects. However, with CBD rising in popularity due to its therapeutic benefits, the term potency is now also used to refer to CBD. In this case, a potent CBD strain represents a wide array of therapeutic benefits.

Why THC and CBD Levels Are Important In A Plant

Cannabis potency is important for several reasons. A big one is to be able to differentiate between cannabis and hemp strains. Cannabis, though legalized in several states, is illegal at a federal level. This is because of the presence of the psychoactive compound which is THC.

In 2018, hemp which is a low- THC variety of cannabis sativa L. was legalized at a federal level. For hemp to be considered legal in the US it must contain less than 0.3% THC.  This is one of the major reasons why cannabis growers must always determine the levels of THC in their plants. Should some plants be found to exceed this threshold they will have to be destroyed to prevent them from entering the consumer market.

When growers are selecting cannabis strains or phenotypes to cultivate a key consideration they have to make is the amount of THC or CBD that they want to come up with in each plant. As alluded to earlier, these two are the most popular phytocannabinoids in cannabis. THC and CBD have several similarities but with one major difference; while THC causes euphoria CBD does not. This comes about as a result of a slight difference in their structures that allow THC to bind to endocannabinoid receptors called CB1 that are primarily located in the brain. CBD on the other hand does not bind to these receptors in the way that THC does and as a result THC causes a change in mental status while CBD does not.

THC and CBD are therapeutic compounds that offer a wide array of healing benefits, we shall look at this in the last segment of this article. They also produce different effects that are sought after by recreational cannabis users. Therefore it is important for the cannabis grower to know what they want to offer to the market and plan ahead for it by determining the levels of THC or CBD that will be produced.

When it comes to consumers, it is important to know the levels of THC or CBD in a plant so as to know what effects to anticipate. This information should be readily available to consumers through third- party results which should be posted on the website. New users may be advised to steer clear of high THC strains as these are likely to trigger overwhelming euphoric effects. Those with severe pain on the other hand may benefit more from high THC strains. High CBD strains, on the other hand, are usually suitable for managing severe childhood seizures.

Factors That Influence THC and CBD Levels in Cannabis

Several factors come into play to determine the level of THC or CBD in a cannabis plant. They include the following:

  •         The genetics
  •         The growing conditions and climate
  •         When the cannabis plants are harvested
  •         Sex of the cannabis plants 

Genetics and THC/ CBD Levels

Genetics and THC/ CBD Levels is a complex subject. However, we will try to simplify it.

THCA and CBDA are synthesized during the course of development from the same cannabinoid: CBGA. One factor determines whether THCA or CBDA will be produced. Two different enzymes that lead to this difference are encoded by the same gene.  Each cannabis plant gets two gene copies, with only three available options. It may get two of the A- genes, one of each, or two of the B genes. This determines how much THC and CBD will be produced.

Those with two A genes will have more CBD with minimal THC levels. This includes strains such as ACDC or Charlotte’s Web. Those with one of each will be balanced strains with the same amount of THC and CBD. Lastly, those with two sets of B genes will become THC dominant. This includes strains such as Gorilla Glue or ChemDawg.

Harvesting of Cannabis

THC and CBD are produced in the resin glands of the cannabis plants. These glands are also known as trichomes and have the appearance of sparkly white particles that appear on the surface of the buds. They will be prominent when the plants mature and are visible prominently under a microscope. The production of phytocannabinoids will peak during harvest when the plants are fully mature.

When exposed to heat, the acidic forms of THC and CBD will begin breaking down and converting to their active forms. The acidic form of THC is THCA while that of CBD is CBDA. This means THCA breaks down to THC and CBDA to CBD. In short, the chemical composition changes during maturation. Extending the harvest duration will increase levels of THC and CBD in plants. This is very critical for hemp plants which should not exceed 0.3% THC.

If you are looking to increase THC or CBD levels in your plants you can consider extending the harvest period to allow these phytocannabinoids to peak.

Do Female Varieties Of Cannabis Have More THC?

Lastly, female varieties of cannabis produce higher amounts of cannabinoids than male varieties. Consequently, those looking for higher potencies are better off dealing with female plants than their male counterparts. This explains the concept behind feminized cannabis seeds.

University of Mississippi Experiment

A recent experiment that was conducted by the University of Mississippi threw a spanner in the works. The study was titled: Relative Potency of Male and Female Cannabis Plants.

From history and practice, it is common to write off male cannabis plants due to their low cannabinoid content. This practice has been handed down through thousands of years of cannabis cultivation.

What this study revealed is that females are only more potent during the final stages of development. At this time, the males should be dying and the females should be in full flower or starting to seed. The males could probably achieve similar phytocannabinoid content if they were prevented from flowering by pruning. Unfortunately male cannabis plants are not as easy to manipulate as compared to females. For example, while flowering could be delayed in the female cannabis plant by reducing day length, the same cannot be achieved with the male plant.

In the experiment mentioned, the male and female plants featured identical cannabinoid contents when assessed at 13 and 17 weeks. The males begin to die at about 17 weeks. This was observed with both the high THC strains and the high CBD low THC strains. In some cases the THC content in the males exceeded that in the females. However, the low and intermediate THC strains featured males with significantly lower THC amounts.

The credibility of this data was questioned due to the great variance in growing techniques, degree of maturity, and sampling techniques used. However, this serves as an alert for strains whose cannabinoid content may vary greatly between the males and females.

Growing Condition Affect THC and CBD Levels

When you start growing, there are some things you should keep in mind. Of paramount importance is the growing environment. The environment supports the genetic expression of the plants and this includes the cannabinoid content. If an adequate amount of light is not present the full expression of cannabinoid levels may not be achieved. The same applies for nutrient levels and other environmental conditions such as temperature and humidity.

THC And CBD Limits

Today's cannabis strains are loaded with phytocannabinoid such as THC and CBD. Because both phytocannabinoids have the same origin there has to be a ration for them to co-exist. In short, the two cannot have an infinite concentration, there has to be a limit.

THC amounts may range from less than 1% in hemp cultivars and to a maximum of 35%. CBD levels in most strains will also range between less than 1% to about 25%. In some strains the amount of the two are equal meaning that they have a 1:1 ratio of THC to CBD.

How To Test for Cannabis Potency

One of the most popular ways of testing for cannabis potency is using immunoassay which is readily available. In this case an antibody that is specific to THC or CBD metabolites is usually used. The antibody is tagged with fluorescent light and introduced. The radioactivity present will determine the concentration of urine in the samples.

Gas chromatography or mass spectrometry may also be used to test for THC metabolites.

What is the Importance of Knowing the THC and CBD levels

What’s the fuss about THC and CBD levels?

Phytocannabinoids are important therapeutic compounds found in cannabis. THC and CBD are the most investigated phytocannabinoids due to their therapeutic and recreational potential.

Plants with high amounts of THC may provide relief from the following:

  •       Recreation
  •       Pain relief
  •       Inflammation
  •       Insomnia
  •       Glaucoma
  •       Arthritis
  •       Poor appetite
  •       Anxiety
  •       Depression
  •       Multiple spasticity

If you are looking to enjoy immense benefits from THC, consider the following highest THC strains:

  •         Afghan Kush
  •         Amnesia Haze
  •         Grape Ape
  •         Critical Blue
  •         Dos-si-dos
  •         Girl Scout Cookies
  •         Lemon Kush
  •         Trainwreck
  •        Jack Herer

Plants with high amounts of CBD may provide relief from the following:

  •         Seizures
  •         Inflammation
  •         Pain
  •         Low mood
  •         Migraines
  •        Anxiety
  •         Psychosis
  •        Inflammatory bowel disease

If you are looking to enjoy immense benefits from THC, consider the following high CBD strains:

  •       Remedy
  •        Lifter
  •        ACDC
  •       Charlotte’s Web
  •      Harle- Tsu
  •      Ringo’s Gift

However, you should note that cannabinoid levels may vary within a particular cultivar of cannabis due to the environmental factors. To get a better grasp of how this comes about, consider reading our previous article on cannabis phenotypes.

Does The Level of THC or CBD Affect The Price Of Cannabis?

Cannabis is priced based on a number of factors. For example, some rare strains such as Mendocino Purps or NYC Diesel may cost slightly more for their novelty. Purple cultivars may also be priced higher for their exotic appeal.

The potency of weed also affects pricing. High potency strains are likely to cost more than low potency strains. This is because the former provides stronger effects. However, several other key factors come into play when determining the price of cannabis. The quality of the cannabis plant is one such factor. The product and how it is prepared also matter. Lastly, the brand selling the cannabis product will also have a huge impact on the final price of cannabis.

The CBD and THC levels are an important consideration for anyone in the cannabis supply chain including the end consumer. This will determine the legality, properties, and benefits that can be accrued from the plant. That is why cannabis testing is big business!


Lydia K. (Bsc. RN) is a cannabis writer, which, considering where you’re reading this, makes perfect sense. Currently, she is a regular writer for Mace Media. In the past, she has written for MyBud, RX Leaf & Dine Magazine (Canada), CBDShopy (UK) and Cannavalate & Pharmadiol (Australia). She is best known for writing epic news articles and medical pieces. Occasionally, she deviates from news and science and creates humorous articles. And boy doesn't she love that! She equally enjoys ice cream, as should all right-thinking people.