Dr. Keith Humphreys, professor of psychiatry and behavioral sciences at Stanford School of Medicine, addressed ca**abis use and its effects during a discussion on Andrew Huberman’s podcast. His expertise spans both clinical treatment and policy research, offering insight into how weed impacts individuals despite some high-achieving public figures being open about their use.
Humphreys emphasized that today’s ca**abis bears little resemblance to what was available in previous decades. In the 1980s and 1990s, THC content averaged 3-5%. Current legal market products average around 20% THC. This is roughly four times stronger.
Usage patterns have also shifted dramatically. Approximately 42% of users now consume it daily or nearly daily, compared to occasional weekend use being more common in the past. When combining higher potency with daily use, brain exposure increases by approximately 65 times compared to 1980s patterns.
“It’s a different d**g than what was back there,” Humphreys explained, comparing the potency difference to that between coca leaves and refined powder form.
Humphreys acknowledged initial skepticism about research linking ca**abis to psychotic disorders but has reconsidered as evidence has strengthened. Early Swedish registry studies showed men who used weed in their teen years had higher rates of psychotic disorders in adulthood.
“The evidence has gotten stronger as the d**g has gotten stronger,” he noted. With much more intense use patterns, the potential for psychosis appears more plausible.
His recommendation: Anyone with first-degree relatives who have schizophrenia, schizoid personality, or bipolar disorder should avoid it entirely.
While acknowledging some successful people use weed, Humphreys characterized it as “a performance degrading d**g” overall. Regular use undermines short-term memory, concentration, and detail management, which are essential skills for succeeding in modern society.
“For some people, it undermines their sort of motivation to do much of anything,” he said, noting the phenomenon of “couch lock” is real.
He recounted examples from Palo Alto families where high-achieving students transformed within months of regular use, losing interest in sports and academics they previously excelled at.
Humphreys expressed concern about ca**abis legalization bringing corporate involvement, contrasting it with decriminalization. Legalization creates industries with smart salespeople who increase consumption. He advocates for stricter regulations on advertising, particularly where young people are exposed.
The contrast with decriminalization is crucial: decriminalization means not punishing users while keeping production and sale illegal. Legalization brings in corporations with profit motives tied to maximizing usage.
Despite concerns, Humphreys acknowledged ca**abis likely has legitimate medical applications, particularly for pain management. The cannabinoid receptor system is evolutionarily ancient and exists throughout the body, not just the brain. CBD, the non-intoxicating component, is already used as medication for pediatric seizure disorders.
Research is now easier to conduct since Congress changed regulations around 2020, which should help identify genuine therapeutic uses.
Edibles differ from smoked ca**abis because onset through digestion takes longer. Users may consume more before feeling effects, then experience overwhelming intoxication when everything hits simultaneously.
Product quality control is also problematic. Unlike regular cookies where chocolate chips distribute evenly, ca**abis edibles sometimes have uneven concentration, meaning one bite could deliver the entire dose.
Like all influences on developing brains, ca**abis effects are most concerning during adolescence. Brains are highly plastic when young, making this the period when problems most readily develop. First psychotic breaks typically occur around ages 18-21.
“Initiating a su**tance when you’re 50 is far less likely to end you up with problems than when you’re young,” Humphreys explained.
The visibility of successful weed users creates misleading impressions. These individuals often have substantial social capital, strong incentive structures, and resources that buffer them from consequences. “You can’t overgeneralize from a sort of a lucky life or a cosseted life,” Humphreys cautioned. What works for someone with extensive support systems may not translate to someone without those safety nets.
Humphreys’ perspective balances recognition of genuine medical potential against concerns about commercial exploitation and individual harm. The key factors determining risk include age of first use (younger is worse), family psychiatric history, frequency and potency of use, and individual life circumstances and support systems
For parents worried about adolescent use or adults considering c**abis, his advice centers on understanding that today’s products are fundamentally different from previous generations, carry real risks especially for developing brains, and that the only guaranteed way to avoid problems is never starting use.
