An article in the journal Addiction recently grabbed my attention.[i] In “Daily or near-daily cannabis and alcohol use by adults in the United States,” Jonathan Caulkins reported that 2022 marked the year daily, or near-daily (i.e., at least 20 days each month), cannabis users outnumbered daily, or near-daily, alcohol users for the first time. While the total number of Americans consuming alcohol is still greater than those using cannabis, heavy users of each tells a different story. An estimated 17.7 million Americans use cannabis every day, or nearly every day, while 14.7 million use alcohol at the same frequency. This raises the question of the degree to which this rate of heavy cannabis use might be problematic.
I spent nearly three decades reviewing the latest cannabis research every month to reach fact-based conclusions about cannabis rather than relying on mere opinion. Most people’s opinions rest on only a limited view of the world, including personal and family experience, a few hundred acquaintances, studies carried by popular media, and public policy positions staked out by their favored politicians. These sources of information lack the wider perspective achieved by scientific studies of whole populations and detailed laboratory research of brain structure and mental functioning in very frequent versus occasional cannabis users and nonusers, both adolescent and adult onset of use. I compiled and organized these decades of research articles in From Bud to Brain (2020) to provide the concrete evidence needed to better inform opinions about cannabis.[ii] The following facts distinguish daily, or near-daily, cannabis users from occasional and nonusers:
- Daily cannabis use reduces the number of functioning cannabinoid receptors in rats by 20 to 60 percent, depending on the brain area being measured.
- Daily, or near daily, human cannabis users have 20 percent fewer cannabinoid receptors in their frontal lobes, the seat of our executive functions. With fewer receptors, the normal endocannabinoid system (which helps regulate things like mood, cognition, and reward) doesn’t work as effectively.
- It takes four to six weeks of abstinence to rebuild cannabinoid receptors to normal levels in the frontal lobes.
- Daily, or near-daily, cannabis use reduces hippocampal volume by 12 percent. The hippocampus is the seat of short-term memory.
- Daily, or near-daily, cannabis use reduces amygdala volume by up to 7 percent. The amygdala is the seat of emotions and novelty.
- Very early onset of heavy cannabis use (under 17) permanently reduces IQ by an average of 8 points.
- Heavy cannabis use reduces executive functions, especially in adolescents.
- Heavy cannabis use reduces memory, measured by recall of a list of random words (RVALT).
- Heavy cannabis use produces a measurable decline in mental flexibility (Wisconsin Card Sort).
- Heavy cannabis use makes users less able to concentrate on one set of stimuli while exposed to an interfering set of stimuli (Stroop Test).
- Heavy cannabis use increases impulsivity (Go/No-Go Test).
- Heavy cannabis use decreases assessment of risk (Iowa Gambling Test).
- Heavy cannabis use decreases awareness of errors (modified Stroop).
- Heavy cannabis users have decreased fine motor skills (Maze tracing).
- Heavy cannabis users (especially of high THC products) have four times the rate of schizophrenia-like psychosis.
While this list of negative effects that linger long after the acute high from cannabis in heavy users looks scary, most are subtle enough to require sophisticated neurocognitive testing to be detected. Except for the IQ decline in early adolescent users, the higher risk among cannabis users with addictive disease, psychiatric conditions such as schizophrenia, bipolar, and major affective disorders, and effects on developing fetuses in pregnant users, the nuanced decrements in memory, executive functions, concentration, fine motor skills, etc. listed above in heavy cannabis users are generally not noticed (although significant others are often bothered by their partner’s failure to notice emotional cues).
I believe daily, or near-daily, cannabis use is most problematic for individuals interested in optimal mental and physical functioning. Those in safety-sensitive activities, such as pilots, surgeons, bus and truck drivers, for example, and certain sports, such as rock climbing, may want to preserve optimal functioning. Likewise, athletes, artists, psychotherapists, and sales personnel may want to maintain optimal performance, especially in reading subtle interpersonal cues.
On the other hand, many heavy cannabis users perceive benefits from their use, and these benefits need to be weighed against any negative impacts on mental and physical functioning. Everyone is responsible for weighing the benefits and costs of daily or near-daily cannabis use. I believe calculating this cost-benefit ratio is improved by acknowledging and understanding the potential costs.
The bottom line for most heavy cannabis users is that they are most likely to be aware of the negative effects of reducing or refraining from use. Psychoactive drugs all seem to obey the bio-physics rule of what goes up must come down. The impact of heavy cannabis use is often felt most in its absence, when people experience the effect of having reduced their brain’s cannabinoid receptors. A cannabinoid deficiency state is an unpleasant experience consisting of anxiety, physical restlessness and agitation, boredom/ennui or anhedonia, decreased appetite, and insomnia, and people are very conscious of these uncomfortable feelings (see “5 Signs of Using Cannabis Too Frequently” for more detail).
Finally, a few daily or near-daily cannabis users become enthralled with cannabis. To be “in thrall” to cannabis means to have one’s fascinated attention captured by cannabis, so that it gains power over one’s life.
