Growing Cannabis In Canada

THC Levels in Cannabis: Why Today's Weed Is So Much Stronger

Humans have used cannabis for thousands of years, but the push for high-THC cannabis is surprisingly recent. In fact, scientists didn't even know what THC (tetrahydrocannabinol) was until 1964, when chemist Dr. Raphael Mechoulam first isolated the molecule. Before then, people knew cannabis had effects whether eaten or smoked, but researchers weren't sure whether one compound or many were responsible.

Today, cannabis potency is higher than ever. According to Health Canada, average THC levels in dried cannabis have climbed from about 3% in the 1980s to roughly 15% today. When Canada legalized cannabis in 2018, a 20% THC product was considered strong. Now, 30% is common, and some pre-rolls are marketed at 44% THC or more.

So how did cannabis get so strong, how high can THC levels actually go, and do consumers even understand what these numbers mean?

A Brief History of Rising THC Levels

According to Jon Page, a botanist, plant biochemist, and adjunct professor at the University of British Columbia (and former chief science officer at Aurora), cannabis potency rose in several distinct phases over the past 50 years.

Phase 1: Early Selection for THC (Pre-1970s)

In regions like Lebanon, Afghanistan, and India, cannabis producers began favouring plants with stronger psychoactive effects. Page describes this as low-level selection for higher THC that continued until roughly the 1970s.

Phase 2: The Globalization of Cannabis (1970s)

In the 1970s, travellers on the "hippie trail" through Asia brought cannabis seeds home. Growers in places like Humboldt County, California, and Amsterdam selected seeds from high-potency regions and began cross-breeding them. These early breeders didn't need labs; they judged strength by how high a joint got them and kept selecting the best results.

Phase 3: Indoor Growing and the War on Drugs (1980s–2000s)

The U.S. War on Drugs and programs like California's Campaign Against Marijuana Production (CAMP) pushed growers indoors. This led to the rise of hydroponics and indoor grow lights. As Page explains, the plant already had the genetic potential for high THC, and controlled indoor growing finally unlocked it. This was the era of "BC Bud," when THC levels climbed into the 20–25% range.

Phase 4: Legalization and Competition (2018–Today)

Legalization in Canada and in many U.S. states brought investors and fierce competition. According to Page, that competition has driven major improvements in growing techniques, pushing potency even higher. Throughout all these phases, one factor stayed constant: producers followed consumer demand for stronger cannabis.

How Does a Cannabis Plant Produce THC?

THC and other cannabinoids are found on cannabis rather than in it. They're produced in trichomes, tiny hair-like structures (the word comes from the ancient Greek for "hair") that grow mainly on the buds.

Cannabis goes through two main life stages:

1. Vegetative stage: The plant grows its classic five-point leaves but produces no THC or CBD. Indoor growers typically give plants 18 hours of light and 6 hours of darkness during this stage.
2. Flowering stage: When light is reduced to 12 hours on and 12 hours off, the plant begins flowering, and trichomes start producing cannabinoids.

UBC botany professor Lacey Samuels explains that each trichome contains disc cells where cannabinoids are made, topped with a cap that resembles a mushroom. Decades of breeding have produced plants with a much higher density of trichomes than wild cannabis had thousands of years ago, when trichomes mainly helped protect the plant from insects. More trichomes means more THC.

THC Percentage Chart: What Counts as Strong?

When cannabis is labelled as 20% THC, it means THC makes up 20% of the dried bud's total weight. Here's a simple guide to THC potency:

What Is the Maximum THC Level in Cannabis?

Most botanists and plant scientists put the natural upper limit for THC in cannabis flower at around 30%. The reason is basic biology.

Professor Samuels suggests a simple thought experiment: if a flower is 25% THC, what makes up the other 75%? A plant always needs cellulose, pectin, and wax to hold the resin inside the trichomes, plus enough healthy plant tissue to carry out photosynthesis. There's only so much room for THC before the plant can't function.

That's why marketing claims of 40%+ THC flower deserve some skepticism. Even Health Canada notes that some strains average as high as 30% THC.

Do Cannabis Consumers Understand THC Levels?

Not really. David Hammond, a professor at the University of Waterloo's School of Public Health, says North American surveys show that about three-quarters of cannabis users don't know the THC level of the products they use. And most of the remaining quarter who say they know are wrong, giving answers for flower ranging anywhere from 0% to 100%.

Consumers do slightly better with cannabis oils, which are often used medically, and with edibles, where Canada's 10 mg-per-package limit makes dosing easier to understand. But for flower, Hammond says guessing whether 30% THC is low, medium, or high is essentially random for most people, based on national surveys of tens of thousands of respondents.

Part of the problem is history: after nearly a century of prohibition in Canada, most people bought cannabis on the black market, with no testing or labelling at all.

Should Cannabis Have a "Standard THC Unit"?

Hammond proposes a solution borrowed from alcohol: a standard "THC unit." Most people understand that a bottle of beer, a glass of wine, and a shot of whisky contain roughly the same amount of alcohol, even though their percentages differ. A similar standard for cannabis would let consumers compare flower, edibles, and concentrates more easily.

This idea is gaining support among researchers. A 2024 paper co-authored by Hammond in the International Journal of Drug Policy explores how a standard THC unit could work in Canada's legal market, and the Canadian Centre on Substance Use and Addiction has published a report on the concept. Researchers have proposed setting one standard unit at 5 mg of THC for all cannabis products.

Ideally, one THC unit would be set at a level where most people feel some effect but stay below the point of feeling intoxicated, just like one standard drink. The goal isn't to make every experience identical, but to give consumers a reliable starting point.

Cannabis Use in Canada by the Numbers

According to Statistics Canada, cannabis use in 2023 looked like this:

• 38.4% of Canadians aged 18–24 used cannabis in the past year
• 34.5% of those aged 25–44 used cannabis
• 15.5% of Canadians 45 and older used cannabis

Canadians spent $4.7 billion on legal recreational cannabis in the 2022/2023 fiscal year, with 64.9% of that going to dried flower. For more data, see Statistics Canada's Cannabis in Canada overview and Health Canada's Canadian Cannabis Survey results.

Genetics Matter: Choosing the Right Cannabis Seeds

As the history of THC shows, a plant's potency starts with its genetics. Growing conditions help a plant reach its potential, but the strain sets the ceiling. That's why choosing quality seeds is the first step for any grower, whether you're after a high-THC strain or a balanced THC:CBD variety.

At Montreal Cannabis Seeds, we offer carefully selected feminized, autoflowering, and regular seeds, with clear strain information so you know what you're growing. Always check your local laws before growing cannabis at home.

Frequently Asked Questions About THC Levels

What is the average THC level in cannabis today?
According to Health Canada, the average is around 15%, up from about 3% in the 1980s. Many legal products now test between 20% and 30%.

What is considered a high THC percentage?
Anything from 15–20% is considered strong, and 20% or higher is very strong.

Can cannabis flower really have 40% THC?
It's unlikely. Most plant scientists place the biological limit for flower at around 30% THC, since the plant needs the rest of its mass to survive and hold its structure.

Why is cannabis stronger now than in the past?
Decades of selective breeding, advances in indoor growing, and market competition after legalization have all increased trichome density, and with it, THC content.