Does Marijuana Grow Brain Cells? What the Neurogenesis Studies Show (2026)

By James Buddsey · Updated October 14, 2026

There is no evidence that marijuana grows new brain cells in people: the studies behind that claim were done in rats and mice, mostly with lab-made cannabinoids or purified CBD, not smoked cannabis. Other animal studies found that THC given to adolescent rats reduced markers of new neurons. Whether adult humans make meaningful numbers of new neurons at all is still debated by scientists.

The headline “marijuana makes brain cells grow” has circulated since 2005, when a Canadian lab reported new neurons in rats given a synthetic cannabinoid. Two decades later, the picture is more complicated. This page explains what that study actually found, what later research added, and why none of it tells you that using cannabis is good for your brain. It is current as of October 2026 and is part of our cannabis research library.

Evidence at a Glance

What Is Neurogenesis, and Why the Hippocampus?

Neurogenesis is the birth of new neurons from stem and progenitor cells. In adult rodents, it happens in a small region of the hippocampus called the dentate gyrus. The hippocampus is involved in learning, memory and the response to stress, so researchers want to know what speeds up or slows down new neuron production there.

The hippocampus is also rich in cannabinoid receptors. Reviews describe the endocannabinoid system as one of the main regulators of signaling and plasticity in this region, and note that chronic stress changes hippocampal CB1 receptor levels (Scarante 2017). That overlap is why cannabinoids became a target for neurogenesis research.

The 2005 Saskatchewan Rat Study

The study behind most “marijuana grows brain cells” headlines came from a psychiatry research team at the University of Saskatchewan and published in the Journal of Clinical Investigation (Jiang 2005). Key points:

• The drug was not cannabis. Researchers used HU-210, a potent synthetic cannabinoid made in a lab, not THC or plant material.
• The subjects were rats. Rat hippocampal stem cells carried CB1 receptors, and HU-210 made cultured embryonic stem cells multiply.
• Chronic, not acute, dosing mattered. Repeated HU-210 treatment increased new neurons in the adult rat dentate gyrus. A single dose did not.
• Behavior changed. Treated rats showed anxiety-reducing and antidepressant-like behavior in standard lab tests. When the researchers blocked neurogenesis with X-ray irradiation of the hippocampus, those behavioral effects disappeared too.

The authors noted that most drugs of abuse studied up to that point decrease adult hippocampal neurogenesis, which is what made the result surprising. It was a well-designed animal study. It was not evidence that smoking cannabis produces new neurons in people.

What Later Animal Studies Found

CBD in stressed mice

A Brazilian team gave mice CBD daily during 14 days of chronic unpredictable stress. CBD increased the proliferation of hippocampal progenitor cells and new neurons, and it prevented stress-induced anxiety behavior. In mice genetically engineered so that neurogenesis could be switched off, CBD no longer had its anti-anxiety effect (Campos 2013). A follow-up found the effect depended on CB1 and CB2 receptors, not the serotonin 5-HT1A receptor, and that CBD also increased dendritic spine density (Fogaça 2018). Both studies used injected CBD at 30 mg/kg, a dose that does not translate directly to a person using a CBD product.

THC in adolescent rats

Studies of THC itself, especially in young animals, point the other way:

• Adolescent rats given daily THC while learning a maze had a smaller boost in plasticity markers and fewer immature neurons than untreated rats in training. THC had no such effect in untrained rats (Steel 2014).
• Adolescent male rats given escalating low doses of THC showed, as adults, impaired spatial memory along with fewer proliferating stem cells, fewer new neurons and lower BDNF, a protein that supports neuron growth (Poulia 2021).

THC in old mice

A 2017 study in Nature Medicine gave mice aged 12 and 18 months a low daily dose of THC. Their performance on learning and memory tasks improved, synaptic proteins and hippocampal spine density rose, and gene activity in the hippocampus of 12-month-old treated mice resembled that of 2-month-old mice (Bilkei-Gorzo 2017). The study measured synapses and gene expression, not the birth of new neurons, and it has not been shown in people.

Mixed signals overall

Even early reviews found the endocannabinoid system pulling in different directions: endocannabinoids stimulated neural progenitor proliferation in some experiments and inhibited hippocampal neurogenesis in others (Galve-Roperh 2006). The result depends on the compound, the dose, the age of the animal and what it is doing at the time.

Do Adult Humans Even Make New Neurons?

This is the biggest gap between the rat studies and your brain. Two major 2018 papers, both based on human brain tissue, reached opposite conclusions:

• A UCSF-led team found that young neurons in the human dentate gyrus declined sharply in the first year of life and were not detected in adults aged 18 to 77 (Sorrells 2018).
• A Columbia-led team examining autopsy hippocampi from healthy people aged 14 to 79 found thousands of immature neurons and similar numbers of progenitor cells across ages (Boldrini 2018).

If the scientific community cannot yet agree on how much neurogenesis happens in adult humans, a drug’s effect on it in people is far from established. No study has measured new neuron formation in human cannabis users.

What Human Brain Studies Show Instead

Research in people looks at brain structure and thinking, not neuron birth. A meta-analysis of 30 structural MRI studies found that regular cannabis users had smaller hippocampal and orbitofrontal cortex volumes than non-users, though the differences were not tied to how long or how much people used, and similar patterns appear with other substances (2019 meta-analysis). These are associations, not proof that cannabis caused the difference.

The National Academies found moderate evidence that cannabis use impairs learning, memory and attention in the short term, and limited evidence of lasting impairment after people stop (NASEM 2017). The CDC notes that the brain keeps developing until about age 25 and that use before 18 may affect how it builds connections (CDC). For the full picture, see our pages on cannabis and brain damage and cannabis and IQ.

Risks and Side Effects

• Short-term memory and attention. Acute impairment of learning, memory and attention is supported by moderate evidence (NASEM 2017).
• Young people. Animal studies of adolescent THC exposure show reduced neurogenesis markers, and the CDC warns that teen use may affect brain development.
• Mental health. The National Academies found substantial evidence linking cannabis use to schizophrenia and other psychoses, with the highest risk among the most frequent users.
• Dependence. Regular use can lead to cannabis use disorder. See our guide to marijuana addiction.

Talk to Your Doctor

If you are considering cannabis or CBD for anxiety, depression or memory problems because you read that it grows brain cells, talk to a doctor first. The FDA has not approved CBD or cannabis for any mental health condition (FDA), and approved treatments exist with far stronger evidence. Our page on cannabis and depression covers the human trials.

Marijuana and Brain Cell Growth FAQ

For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.