Potency of Marijuana
How Strong is Marijuana?
The main ingredient in marijuana responsible for its psychoactive, or mood altering, effects is a
cannabinoid called delta-9-tetrahydrocannabinol, or "THC" for short. In combination with other
cannabinoids, the amount of THC in marijuana determines the strength of the effect of the drug.
The level of THC in marijuana is not always the same. It can vary depending on the strain or
variety of the plant, the way in which the plant is grown, the part of the plant that is used, and the
way the plant is prepared for use and how it is stored.
Strain and Cultivation Technique
The way marijuana is grown can affect the amount of THC in the plant, and therefore its potency.
Cannabis sativa is the species of plant that most commonly produces the drugs known as
marijuana, hash, or hashish. Normally, the male cannabis plant fertilizes the female plant. If
female plants are grown in isolation, then the flowering tops of the plant remain unfertilized.
These unfertilized flowering tops, known as “sinsemilla," have particularIy high THC levels.
Crossbreeding and genetic selection can also produce strains of the cannabis plant with
particularly high levels of THC.
Some argue that cannabis grown hydroponically or under artificial light is stronger than cannabis
grown outdoors in natural light. Because the amount and quality of resin produced depends on
temperature, humidity, light, and soil acidity. Cannabis grown outdoors varies considerably in
potency, whereas intensive indoor cultivation, often done with female plants and clones, under
artificial light, and without soil, produces optimized cultivation conditions and cannabis of a
consistently higher potency (UNODC, 2009). Some users of the drug say they can tell when they
are using "hydro" cannabis versus “bush weed" because the effects are so much stronger.
However, some people do not believe it is hydroponic cultivation itself that makes cannabis
stronger; large scale hydroponic cultivators may simply be more likely to use more potent strains
and grow plants to their full potential.
Part of Plant Used
The flowering tops, or "buds" of the female cannabis plant have the highest concentrations of
THC, followed by the leaves. Much lower THC levels are found in the stalks and seeds of the
Preparation for Use
The cannabis plant can be prepared in different ways for use, and these different forms have
different potency. The strongest preparation is known as "hash oil," which is made by extracting
THC from the cannabis plant in oil. Hash oil has been found to contain 15% to 30% THC. The
resin secreted from the plant can be dried to make "hash," which is the second strongest
preparation. Hash has THC concentrations ranging from 10% to 20%. The form with the lowest
THC level is tire dried buds and leaves of the plant, commonly known as marijuana. Marijuana is
the most common form of cannabis available in the USA and can vary widely in potency from
less than 1% to 20%.
Has Marijuana Become Stronger?
The marijuana used today is stronger than it used to be, but not as strong as has been written in
some media reports (claiming marijuana is 30 times stronger today than during the 1970s).
Depending on how analysis was conducted and the sample analyzed, marijuana strength has
increased by 2 to 7 times since the 1970s, measured by THC levels.
Another difference between then and now is that marijuana users in the 1970s were more likely
to smoke the leaves and to initiate use around 20 years of age. Marijuana users today,
however, often start in their mid-teens and prefer to smoke the more potent flowering tops,
(buds) of the plant. Research shows that young, regular (daily or near daily) users are most at
risk for many of the adverse effects of marijuana, including mental health problems and
So what’s the Story?
Anecdotal reports as well as measurement in lab tests suggest that cannabis used today is
stronger than in the past. Based on available scientific evidence, it would appear that the
strength of marijuana has increased to some extent over the last 25 years, though far less than
is sometimes claimed.
Instead, it is likely that the main difference today is the part of the plant people smoke and the
age at which people begin regular use. It is more common for people today to smoke the
flowering heads of the plant which are much more potent than the leaf product. These changes
in the patterns of use may result in users of today taking in higher levels of THC than in the past.
Additionally, the younger age at which people start and the more regularly they use, the more
likely they are to be adversely affected by marijuana. Simply focusing on marijuana potency may
obscure the fact that young regular users are most at risk of marijuana related harm.