Cannabis and mental health: psychosis risk, potency and young brains

The Short Version

Four Huberman Lab conversations agree on a core warning: for some people, cannabis worsens mental health, the risk is highest for the young and the genetically vulnerable, and today's high-THC products are where the danger concentrates [1][2][3][4]. Andrew Huberman, citing a Lancet Psychiatry review, says heavy use carries about four times the risk of later psychosis and that higher THC potency brings higher risk [2]; Stanford psychiatrist Nolan Williams calls THC pro-psychotic and would not want a teenager using it before about age 25 [4]; and Harvard psychiatrist Chris Palmer says THC acts on receptors on mitochondria and that heavy adolescent users show brain shrinkage [3]. Cannabis researcher Matthew Hill agrees that cannabis is off-limits for anyone with schizophrenia or a close relative with schizophrenia or bipolar disorder, calling it "fuel on a fire," but he disputes that it causes schizophrenia in people who wouldn't otherwise develop it, and argues concentrates, not strong flower, are the real potency problem [1]. The evidence-based middle ground: legal isn't the same as safe, but neither is cannabis a universal cause of madness.

Table of contents

What They Said

Andrew Huberman: the developing brain is the red line

In his solo episode on cannabis, Huberman is measured through most of the biology, then openly alarmed when he reaches pregnancy and young people [2]. He reads from a 2022 systematic review in Lancet Psychiatry, "Association of Cannabis Potency with Mental Ill Health and Addiction," which he says looked at more than 4,000 studies and kept only the most rigorous [2].

His reading of it is stark. "Heavy cannabis use meaning cannabis use more frequent than twice per week has been associated with four times the risk of psychosis later in life," he says, "in particular" schizophrenia and bipolar-like episodes [2]. Both conditions have a strong genetic component, and he says that "using cannabis especially during adolescence in the teen years and up until age 25 create a four times greater risk of psychosis for those that have a predisposition to bipolar disorder and or schizophrenia" [2]. On potency, he says the review, the first systematic look at the question, points to one conclusion: "the more potent the THC concentration the higher probability of developing psychosis or a major depressive episode or a major anxiety disorder later in life" [2]. With new, engineered high-THC strains, "the risk of psychosis is going up and up," he warns, unless use in adolescents and people 25 or younger drops to zero or to very low frequency and potency [2].

Early use and brain structure. Starting as young as 12 to 14 more than doubles the later risk of psychosis, Huberman says [2]. A large consortium study in Translational Psychiatry found that adolescent cannabis use accelerates thinning of the prefrontal cortex's gray matter in a dose-dependent way, the region responsible for planning, emotional control and organizing one's life [2].

Who's using. Use is highest among 16 to 24 year olds, the average age of first use is about 19, and roughly 20% of that age group use daily [2]. Many are students or employed, and he worries that the public message, "that it's not as bad as alcohol and maybe not that bad and maybe even has health benefits," sets young people up to start without realizing the consequences [2]. He calls the psychiatric risk a kind of "time release" on "the development of psychosis and other types of major psychiatric disorders later in life" [2].

Depression and anxiety. Huberman says cannabis's anxiety-relieving effects fade over about 12 months or more of chronic use, as a system used to being "tickled not punched" reduces receptors and signaling [2]. People then need more, and anxiety can worsen on and off the drug [2]. He says cannabis use makes people about four times more likely to develop chronic major depression, often in people who weren't depressed before, while depression does not strongly predict starting cannabis [2].

Paranoia doesn't get fixed by more. Some people experience intense anxiety and paranoia regardless of strain, and there's no reliable way to predict who [2]. Huberman says the "dorm room" advice to simply use more if cannabis makes you paranoid is "absolutely categorically false," since cannabis tends to produce the same effect each time [2].

Pregnancy. Huberman says surveys suggest about 15% of pregnant mothers in the U.S. use cannabis, often edibles or CBD products assumed to be safe [2]. Because CB1 receptors are essential to every stage of fetal brain wiring and THC and CBD cross the placenta, he calls the statistic "absolutely terrifying" and urges anyone pregnant, trying to conceive or breastfeeding to avoid cannabis, THC and CBD in any form [2].

His balance. He doesn't condemn occasional adult use, acknowledges well-demonstrated benefits for chemotherapy nausea, some pain and glaucoma, and notes that many harms came from prohibition itself [2]. But he rejects the "not as bad as alcohol" argument, and for those who used heavily when young, suggests quitting and supporting the brain with cardiovascular exercise, sleep, nutrition and social connection [2].

Matthew Hill: "fuel on a fire," not a cause

Hill, a professor at the University of Calgary's Hotchkiss Brain Institute, came on the show after criticizing Huberman's solo episode, especially the claim that cannabis causes psychosis [1]. He says he gets hate mail from both pro- and anti-cannabis camps, and much of his contribution is separating what the data show from what people believe [1].

Where he's firm. Hill is clear that people with schizophrenia use cannabis more and that it can trigger psychotic episodes in them: "if someone has schizophrenia cannabis is contraindicated." [1] He would also tell anyone with a first-degree relative with schizophrenia or bipolar disorder to avoid it [1]. In vulnerable people, he says, "cannabis is fuel on a fire": it can bring on a first episode sooner and worsen the long-term outlook [1]. Acute cannabis-induced psychosis can happen, but he says it's rare [1].

Where he pushes back. Hill argues the evidence doesn't show that cannabis causes schizophrenia in people who wouldn't otherwise develop it [1]. His reasons:

• Schizophrenia rates didn't shift as cannabis became mainstream after the 1960s [1].
• Rates are similar in North America and Scandinavia despite very different teen use [1].
• At least three genetic studies suggest genetic risk for schizophrenia predicts cannabis use more than the reverse [1].
• If cannabis caused schizophrenia in some people, it would have to prevent it in an equal number for rates to stay flat [1].
• Some patients tell him cannabis eases the negative symptoms their medications don't treat, which can create a vicious cycle, much as people with schizophrenia smoke many cigarettes [1]. Huberman compares it to adults with ADHD self-medicating with stimulants [1].

On potency. Hill also disputes the idea that high-potency "skunk" is the key driver, noting that the foundational 1987 study of Swedish conscripts involved cannabis of about 2 to 5% THC [1]. A more parsimonious explanation, he suggests, is that vulnerable people seek out the strongest cannabis available [1]. But he is not relaxed about potency in general. Cannabis from the 1970s was around 5% THC; most commercial flower today is 20 to 30% [1]. Studies by Colorado researchers using a mobile lab found that people smoking 20 to 30% flower still ended up at about 100 ng/ml of blood THC, the same as lab subjects smoking weaker cannabis, because they took fewer puffs [1]. The real problem, he says, is concentrates such as dabs, oils and distillates, which can reach 90% THC or more, are nearly impossible to titrate, produce blood levels of 200 to 300 ng/ml and cause much stronger tolerance [1]. From a public health view, he'd focus far more on access to concentrates than on potent flower, while noting that inexperienced or especially sensitive people can still take too much strong flower quickly [1].

Edibles. Most adverse events, Hill says, happen because people feel nothing after half an hour of an edible, take more, and then get hit hard; effects start 30 to 90 minutes after eating and last four to six hours or longer [1]. Canada is working on standardized dose units, and his take-home is to go low and slow [1].

Anxiety and dose. Hill describes cannabis's anxiety effects as biphasic: low doses calm anxiety, higher doses can flip into anxiety, even in the same person [1]. Mouse studies by Giovanni Marsicano and Beat Lutz suggest low doses quiet excitatory transmission, including in the amygdala, while high doses shut down inhibition and amplify activity [1]. Setting matters too: a 1970s study that gave THC before oral surgery produced panic in nearly everyone [1].

Addiction. Hill says cannabis use disorder is real, with criteria matching other use disorders [1]. Older estimates put the conversion rate at 9 to 11% of users, but among weekly users it may be closer to 30% [1]. He stresses that people confuse legality with safety; Canada legalized to reduce the harms of prohibition, not to endorse cannabis as safe [1].

Who is using now. About five and a half years into legalization in Canada, the biggest proportional increase has been among adults over 55, especially women, and young adults aged 20 to 24 use more [1]. Teen use, already high (35 to 40% of 12th graders have tried it, about 5% use nearly daily), hasn't risen and has dipped slightly in some U.S. states [1]. Hill worries that people selling cannabis, not doctors, have become the main source of information, and cites a Colorado study in which about 80 to 85% of dispensaries recommended cannabis for morning sickness [1].

Why THC is different from your own cannabinoids. Hill explains the intoxication mechanism: drugs that raise the body's own anandamide produce no high, because endocannabinoids act at specific synapses at specific moments, whereas THC is "just blanket activation you just carpet bombing the whole system indiscriminately" [1]. He corrects Huberman's earlier description of THC as a sledgehammer: it's a high-affinity partial agonist, closer to anandamide [1].

Nolan Williams: THC is pro-psychotic, CBD the opposite

Williams, a Stanford psychiatrist and neurologist whose lab develops treatments for severe depression, frames cannabis's effects largely by the ratio of THC to CBD [4]. CBD is anti-epileptic and anti-psychotic, he says, as seen in the THC-free strain Charlotte's Web and in trials for severe childhood seizure disorders, while THC is pro-psychotic and pro-epileptic [4]. High-THC products have caused psychosis that resolves once THC clears [4]. And humans have bred CBD out of many strains [4].

He would not want a teenager using cannabis before the prefrontal cortex matures, around 25, though he sees occasional use by a healthy adult as relatively safe for most people [4]. In the same conversation, Huberman cites the Lancet Psychiatry report linking early use of potent cannabis to later psychosis [4]. Williams also discusses a David Nutt analysis ranking drugs by combined personal and societal harm, which placed alcohol as most harmful, ahead of heroin and cocaine [4]. His general stance on psychoactive drugs used for mental health is that they belong under medical supervision; of psychedelics he says "these drugs can't be recreational drugs" [4].

Chris Palmer: cannabis as a hit to brain metabolism

Palmer, a Harvard psychiatrist known for linking metabolic health and mental illness, places cannabis in a list of risk factors that he says impair mitochondria: sleep disruption, stress and trauma, alcohol, tobacco and cannabis [3]. THC acts on CB1 receptors located directly on mitochondria, he says; studies in Nature found these receptors drive many of marijuana's effects, and heavy adolescent users show shrinkage in brain areas rich in them [3]. The same receptors appear to underlie THC's memory impairment and lack of motivation [3]. Mitochondria can recover, Palmer says, but chronic use likely harms both mental and metabolic health [3]. In his broader theory, mitochondria regulate neurotransmitters, hormones, gene expression and inflammation, all disrupted in mental illness, which is why an insult to them would ripple outward [3].

Where They Agree, and Where They Don't

Firm consensus.

• Anyone with schizophrenia, or a first-degree relative with schizophrenia or bipolar disorder, should avoid cannabis [1][2]. Hill calls it contraindicated in schizophrenia [1]; Huberman's cited review finds the fourfold psychosis risk concentrated in the genetically predisposed [2].
• Young brains are more vulnerable. Huberman draws the line at about 25 [2], Williams at the maturation of the prefrontal cortex around 25 [4], and Palmer cites shrinkage in heavy adolescent users [3]. Hill doesn't set an age cutoff, but doesn't dispute that cannabis accelerates illness in those vulnerable to it [1].
• THC is the psychiatric problem, and CBD is not the same thing. Williams calls THC pro-psychotic and CBD anti-psychotic [4]; Huberman highlights THC potency [2]; Hill explains why THC's indiscriminate action differs from the body's own signaling [1]. Both Hill and Williams note that breeding for THC has largely eliminated CBD from street cannabis [1][4].
• Higher doses mean more anxiety and more risk: Hill's biphasic anxiety effect [1], Huberman's warning that more cannabis doesn't fix paranoia [2].
• Legal does not mean safe, but prohibition caused real harm [1][2].
• Pregnancy is a clear no [1][2].

The causation dispute. This is the central disagreement, and it's a real one. Huberman presents heavy use as associated with a fourfold risk of later psychosis and describes cannabis as creating that risk, especially in the predisposed [2]. Hill accepts the association and the harm to vulnerable people but argues that population data (flat schizophrenia rates, similar rates across countries with different teen use) and genetic studies suggest the arrow runs substantially from vulnerability to cannabis use, not from cannabis to otherwise-absent schizophrenia [1]. Notably, the two positions converge in practice: Huberman's own reading stresses risk "for those that have a predisposition" [2], and Hill's "fuel on a fire" means earlier onset and worse outcomes in exactly those people [1]. Williams sits between them, noting high-THC psychosis that resolves once THC clears [4], a transient, drug-induced state distinct from lifelong schizophrenia.

The potency dispute. Huberman, citing the Lancet Psychiatry review, says higher THC potency brings higher risk of psychosis, depression and anxiety [2]. Hill says the "skunk" explanation doesn't fit the early evidence and that vulnerable people may seek stronger products, and adds that most flower users self-titrate to similar blood levels [1]. But Hill agrees potency matters enormously for concentrates, which can't be titrated [1]. So the sources agree potency is a concern; they differ on whether strong flower is the problem or mainly concentrates.

Depression and anxiety. Huberman says chronic use makes chronic major depression about four times more likely, with anxiety relief fading over time [2]. Hill emphasizes a more mixed picture: in surveys about 85% of users say they use cannabis to reduce stress and anxiety, older studies of synthetic THC suggested anti-anxiety effects, and his lab's hypothesis is that some anxious people have low baseline anandamide [1]. Both agree higher doses provoke anxiety [1][2].

Other corrections Hill made to the solo episode. On several biological points the sources directly disagree, and they matter for trusting specific claims:

• Huberman's solo episode said THC binds with "thousandfold greater potency" than the body's own cannabinoids [2]; Hill says THC is a partial agonist, closer to anandamide, and that its high comes from blanket activation rather than raw strength [1].
• Huberman says smoking clearly raises prolactin [2]; Hill says the most consistent finding is that cannabis lowers prolactin [1].
• Huberman links chronic smoking to gynecomastia [2]; Hill says he hasn't seen compelling evidence it commonly causes it [1].
• Huberman says THC can remain detectable for at least 80 days [2]; Hill says 80 days is not the norm and most people pass after about 30 days of abstinence [1].
• Huberman describes sativa and indica as having different effects [2]; Hill says the labels don't match chemical composition and that "the biggest predictor of what someone feels when they consume cannabis is what they're told on the label." [1]
• Huberman cites surveys of about 15% of pregnant mothers using cannabis [2]; Hill gives estimates from 2 to 20%, with his own guess around 10% [1].

Huberman openly accepted several of Hill's corrections on the show [1].

Why It Works

The sources offer several mechanisms for how cannabis can harm mental health.

Blanket activation of a precision system. The body's endocannabinoids act as a thermostat, released at specific synapses at specific moments to maintain balance [1]. THC activates CB1 receptors everywhere at once, changing how many networks communicate [1]. That indiscriminate action produces the high, and at higher doses the loss of balance.

Dose flips anxiety into panic. At low doses, cannabinoids seem to quiet excitatory transmission, including in the amygdala; at high doses, they shut down inhibitory neurons, which carry about 70% of CB1 receptors, amplifying activity [1]. That explains why the same person can be calmed by a little and panicked by a lot [1], and why potent concentrates and stacked edibles are the common routes to bad reactions [1].

Tolerance erodes the benefit. With repeated THC, the system reduces receptors and signaling [2]; PET imaging shows chronic users have fewer CB1 receptors [1]. People then need more to get the same relief, and anxiety can worsen both on and off the drug [2]. Concentrates produce much stronger tolerance [1].

THC versus CBD. THC is pro-psychotic, while CBD is anti-psychotic [4]. Breeding for THC has nearly eliminated CBD from street cannabis; in one large analysis only about 3% of samples had more than 1% CBD [1]. Modern products thus deliver the psychosis-promoting compound without the counterweight [1][4].

A developing brain is still wiring itself. CB1 receptors are essential to every stage of fetal brain development [2], and adolescent use accelerates dose-dependent thinning of prefrontal gray matter [2]. Because the prefrontal cortex matures around 25 [4], cannabis during adolescence acts on circuits still under construction.

Mitochondrial effects. Palmer's mechanism is that THC acts on CB1 receptors on mitochondria, which govern neurotransmitters, hormones, gene expression and inflammation; heavy adolescent users show shrinkage in brain areas rich in these receptors, and the same receptors appear to drive memory impairment and low motivation [3].

Accelerating an underlying vulnerability. Hill's model is that in people genetically primed for psychosis, cannabis brings on a first episode sooner and worsens the long-term course [1], consistent with Huberman's finding that the fourfold risk concentrates in the predisposed [2]. The strong genetic component of bipolar disorder and schizophrenia [2] explains why family history is the best warning sign available.

Where It Applies, and Where It Doesn't

The warnings apply most strongly to:

• People with schizophrenia or bipolar disorder, and anyone with a first-degree relative with either [1][2].
• Teenagers and young adults up to about 25, especially those starting young; starting at 12 to 14 more than doubles later psychosis risk, per Huberman [2][4].
• Heavy users, defined in the review Huberman cites as more than twice a week [2], and weekly users, among whom use disorder may approach 30% [1].
• Users of concentrates, and people who take more edibles before the first dose kicks in [1].
• Pregnant or breastfeeding people and those trying to conceive [1][2].
• People who've had paranoid or panicky reactions before, since the same reaction tends to recur [2].

They apply less, according to some sources, to occasional use by healthy adults without a family history, which Williams calls relatively safe for most people [4] and Huberman does not condemn [2]. Hill's data suggest flower users mostly self-titrate [1]. And some people may get real benefits: Hill describes evidence for pain (mainly its emotional side), PTSD nightmares and some anxiety [1], and Huberman acknowledges chemotherapy nausea, some pain and glaucoma [2].

Two caveats cut the other way. First, whether cannabis causes schizophrenia in otherwise unaffected people is genuinely contested between these sources [1][2], so the strongest claim the evidence here supports is harm to the vulnerable, not universal harm. Second, much popular information comes from sellers, not doctors [1], and several widely repeated biological claims were corrected on air [1]; consumers should be skeptical of marketing and scare stories alike.

If you have a personal or family history of psychosis, bipolar disorder, depression or anxiety, or are pregnant, talk with a doctor before using cannabis in any form.

What To Do With It

1. Check your family history first. If a parent or sibling has schizophrenia or bipolar disorder, avoid cannabis; Hill and Huberman agree on this [1][2].

2. Wait until at least 25. Williams and Huberman both draw the line at prefrontal maturity, around 25, and Huberman says starting at 12 to 14 more than doubles later psychosis risk [2][4].

3. Avoid concentrates. Dabs, oils and distillates can reach 90% THC or more, can't be titrated and produce two to three times the blood levels of flower [1].

4. Keep frequency low. The review Huberman cites ties the fourfold psychosis risk to use more than twice a week [2], and Hill says use disorder may reach about 30% among weekly users [1].

5. With edibles, go low and slow. Most people feel 5 mg, and nearly everyone feels 10 mg; don't redose after half an hour of feeling nothing, because effects start 30 to 90 minutes after eating and last hours [1].

6. Never take more to fix a bad reaction. Paranoia doesn't resolve with a higher dose, Huberman says; Hill and Huberman agree anyone having a bad reaction should not take more [1][2].

7. Don't trust strain labels. Indica and sativa labels don't reliably predict chemistry, and what you're told on the label shapes what you feel [1]; look at THC and CBD content instead, remembering most street products are THC-dominant [1][4].

8. Stop entirely if pregnant, breastfeeding or trying to conceive. This includes CBD products [2]; Hill adds anyone struggling to conceive should stop to see if it helps [1].

9. Watch for the warning signs of dependence and mood change. Use taking over time and energy, risks to get it, irritability without it [1], or anxiety and depression worsening over months of use [2] are signs to cut back or quit.

10. If you used heavily when young, support recovery. Huberman suggests quitting and prioritizing cardiovascular exercise, sleep, nutrition and social connection [2]; Palmer says mitochondria can recover [3].

Sources

1. Dr. Matthew Hill: How Cannabis Impacts Health & the Potential Risks · Huberman Lab
2. The Effects of Cannabis (Marijuana) on the Brain & Body · Huberman Lab
3. Dr. Chris Palmer: Diet & Nutrition for Mental Health · Huberman Lab
4. Dr Nolan Williams Psychedelics Neurostimulation For Brain Rewiring · Huberman Lab