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How Marijuana Works

Marijuana Potency

Whether marijuana is more potent today than it was 30 or 40 years ago is at the center of much debate. The U.S. federal government has said that the levels of potency have risen anywhere from 10 to 25 times since the 1960s. Is this a myth or reality?

“There’s no question that marijuana, today, is more potent than the marijuana in the 1960s. However, if you were to look at the average marijuana potency which is about 3.5 percent, it’s been relatively stable for the last 20 years. Having said that, it’s very important that what we have now is a wider range of potencies available than we had in the 1970s, in particular.”

That’s from Alan Leshner, the Director of the National Institute on Drug Abuse, while he was testifying in front of the U.S. House Subcommittee on Crime in 1999.

Those who support the legalization of marijuana say that the data are skewed because testing was only performed on marijuana of specific geographic origins in the 1960s and 1970s, and therefore isn’t representative of marijuana potency overall. Officials obtained the samples from a type of Mexican marijuana that is known to contain low levels of THC — 0.4 to 1 percent [source: Kuhn et al.]. When these levels are compared to other types of marijuana, it looks as if potency levels have risen in the last 30 years.

Typical THC levels, which determine marijuana potency, range from 0.3 to 4 percent. However, some specially grown plants can contain THC levels as high as 25 percent, leading to a call by some users for producers to put out mellower Mary Jane [source: Marris]. Several factors are involved in determining the potency of a marijuana plant, including:

  • Growing climate and conditions
  • Plant genetics
  • Harvesting and processing
  • Desire by small growers to maximize profit

The time at which the plant is harvested affects the level of THC. Additionally, female varieties have higher levels of THC than male varieties.

As a cannabis plant matures, its chemical composition changes. During early development, cannabidiolic acid is the most prevalent chemical. Later, cannabidiolic acid is converted to cannabidiol, which is later converted to THC when the plant reaches its floral maturation.

To determine the average potency levels of marijuana, researchers need to examine a cross section of cannabis plants, which wasn’t done in the 1960s and 1970s. This makes it difficult to make accurate comparisons between the THC levels of that period and the THC levels of today. Moreover, establishing a clear relationship between THC levels and impairment is not as straightforward as with, say, blood alcohol content.

In 2011, 57 percent of U.S. businesses required prospective employees to pass a drug test, according to a poll conducted by the Society for Human Resource Management. Drug tests detect the five metabolites that THC breaks down into before passing into urine. Detectable amounts can remain in the system for several days or weeks following use, depending on potency and amount consumed.

One of the most common tests is the immunoassay, in which urine is mixed with a solution containing an antibody specific to certain metabolites, typically tagged with fluorescent dye or a radioactive substance. The amount of fluorescent light or radioactivity indicates the concentration of metabolites in the sample.

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

How Marijuana Works Marijuana Potency Whether marijuana is more potent today than it was 30 or 40 years ago is at the center of much debate. The U.S. federal government has said that the

How to help consumers understand the amount of THC and CBD in their cannabis

Updated March 29, 2018

Cannabis products are required to be tested and labeled for the amount of THC and CBD they contain. Because these two cannabinoids are typically the most abundant in cannabis products, it’s critical for consumers to understand what they are and how they work. Although cannabis packaging contains labels that indicate the amount of THC and CBD in products, these numbers can be difficult to read and interpret, especially for people new to cannabis.

Figure 1: An example cannabis packaging label from Washington state showing a breakdown of the percentage of different cannabinoids present in the flower. (Leafly)

The image above shows an example packaging label from Washington. These labels typically indicate cannabinoid levels (expressed as a % of the dry weight of the product) in small font on the back of packages. Total THC and CBD levels are reported as a percentage of the dry weight of the flower, and are a required part of cannabis product labeling.

In the above example, you can see a variety of values, including numbers for “THC,” “THCA,” and “Total THC.” If you’re new to cannabis, it might not be clear exactly how these numbers are related. It can also be difficult to interpret total THC levels without some more context. Is 21.35% THC an average amount for flower, or is it a lot? To get a better idea of this, it helps to know the full spectrum of possible THC levels.

Fortunately, the biology of cannabinoid production is constrained in interesting ways. Strain genetics limit cannabinoid production in cannabis flower. Although there are several different major cannabinoids produced by cannabis, broadly speaking, there are three major “chemotypes” defined by THC:CBD ratios:

  • THC-dominant strains contain mostly THC and little CBD and will have strong psychoactive effects. Most popular strains, such as Blue Dream, OG Kush, and Granddaddy Purple, fall into this category.
  • CBD-dominant strains contain mostly CBD and little THC and will have little or no obvious psychoactive effects. Charlotte’s Web and Remedy are popular examples of CBD-dominant strains.
  • Balanced strains fall somewhere in the middle. They have THC and some CBD, but generally not as much as THC- or CBD-dominant strains. The strains will get you high, but the effects will be noticeably different from THC-dominant strains. Examples include Cannatonic and Harlequin.

Figure 2: All strains fall into one of three major ‘chemotypes’ based on their ratio of total THC to total CBD. Strains in each group usually have total THC and CBD levels in the ranges shown above. (Amy Phung/Leafly)

As you can see in the above graph, strains naturally fall into one of three major categories (chemotypes) based on their THC and CBD levels. Looking at strains in this way allows us to start to think about specific strains in a broader context, relative to the full spectrum of THC and CBD levels that encompass strains.

We have used thousands of laboratory testing measurements of THC and CBD in cannabis products to map out their full range. Using this data, we’ve come up with some common sense cutoffs for THC and CBD levels so that products on Leafly dispensary menus can be represented by up to five filled-in circles indicating a scale of how much THC and CBD they contain.

Figure 3: Average total THC and total CBD levels for popular strains. Three examples strains each are shown for THC-dominant, CBD-dominant, and Balanced strain categories. (Amy Phung/Leafly)

To make things easier, Leafly’s dispensary listings will begin using this simpler, more intuitive system for their menu items to help consumers judge how much THC and CBD cannabis products have. Instead of just the raw percentages, Leafly users will be able to more easily judge whether cannabis products have high, low, or medium levels of THC and CBD, as well as which major chemotype category they fall into (THC-Dominant, CBD-Dominant, or Balanced). Keep an eye out for this new menu system over the next few weeks, and be sure to let us know what you think.

Figure 4: Leafly’s THC and/or CBD scale for cannabis flower. (Amy Phung/Leafly)

The above THC and/or CBD scale for cannabis flower explains the range of THC or CBD in a package of dried bud to help simplify the information for consumers.

Figure 5: THC/CBD scales for different cannabis product categories; click to enlarge. (Amy Phung/Leafly)

This system is displayed in the following sample menu, where users can now sort by product type (Flower, Concentrates, Edibles, or Pre-Rolls) and expand additional categories (Strain Collection, Indica/Sativa/Hybrid, THC, CBD, Strain, Brand, Price, and Quantity) to narrow down a dispensary’s options to find their ideal strain or product.

Figure 6: An example of Leafly’s new menu system filtered to display flower, edible, and pre-roll products. (Click to enlarge/Leafly)

Clicking on each category in the left sidebar will dropdown options such as checkboxes or sliders that allow users to narrow results down to their preferred findings.

Figure 7: Leafly’s new menu system with an expanded tool tip to help explain each filter option. (Click to enlarge/Leafly)

Of course, THC and CBD aren’t the only things that matter. Cannabis contains a variety of other cannabinoids and rich bouquet of terpenes that shape its aroma, flavor, and effects. As the cannabis industry continues to grow and evolve, we will need to establish a simple and intuitive visual language that allows consumers to quickly and easily explore cannabis strains and products based on all of their key ingredients.

THC and CBD percentages on cannabis product labels can be confusing to consumers if there's no scale explaining potency. Using lab testing data, Leafly has come up with a better system.