It is well established that chronic marijuana use in the teen years causes functional and anatomical changes in the brain and that these changes are somewhat permanent but just how permanent was unknown.1-4

Chronic marijuana use causes thinning of the hippocampus in humans (and animals).  The hippocampus, together with its extensive interconnections with other neural systems, supports the flexible use of information in the brain.  It helps the brain develop lots of different abilities such as: memory, executive function, adaptive reasoning, attention, decision-making, character judgments, language use and main others.5  Chronic and acute marijuana use is known to impair all of these functions with chronic use causing persistence of impairment even after ceasing use of marijuana.1-4  It is thought that the anatomical changes and mental changes are interrelated with the anatomical thinning being representative of either the loss of neurons or the non-functioning of the neurons.1  (Note:  Non-functioning neurons are thought to get thinner if not used much like muscles).

Researchers from California have found that the anatomical changes in the brain persist throughout life and are still present up to 40 years after stopping using marijuana.6  They studied people in their 60’s (average age 66) who had used marijuana heavily during their teens (>20 times/month) but had essentially stopped using it by age 35 (<1-2 times/month).  These individuals still had thinning of the hippocampus in their brains caused by the use of marijuana in their teen years.

Recently, it has been shown that concurrent use of CBD with THC can minimize and possibly prevent the hippocampal thinning caused by THC exposure.2  However, even more recently, researchers found that individuals who were taking THC and  already had hippocampal thinning could have the thinning reversed with the addition of CBD, even if they kept ingesting THC.7

Even though the anatomical changes may be reversed the functional changes associated with THC use may or may not be reversed by CBD.  Pretreatment with CBD has been shown to reduce the hippocampal-dependent memory impairments seen with acute THC use.8  A different cognitive study found that CBD improved facial emotional recognition in THC users acutely. 9 However, a recent study found that the acutely-induced behavioral, subjective, or physiological effects of THC ingestion are not altered with CBD ingestion.10  These difference may be due to the fact that different parts of the brain are being connected by the hippocampus for different tasks.11

Therefore, there appears to be some potential for CBD to reduce some of the acute cognitive changes seen with CBD but whether the potential for CBD to reverse established changes due to chronic THC use is unknown.

Bottom Line:

CBD has the potential to prevent and reverse the anatomical changes in the brain caused by THC.   In addition, CBD has the potential to reverse some of the functional changes seen with acute THC use.  However, the potential for CBD to reverse some of the functional changes caused by chronic THC is unknown.



  1. Ashtari M, Avants B, Cyckowski L, et al. Medial temporal structures and memory functions in adolescents with heavy cannabis use. J Psychiatr Res. 2011;45:1055–1066.
  2. Yucel M, Lorenzetti V, Suo C, et al. Hippocampal harms, protection and recovery following regular cannabis use. Transl Psychiatry. 2016;6:e710–e710.
  3. Solowij N, Battisti R. The chronic effects of cannabis on memory in humans: a review. Curr Drug Abuse Rev.2008;1:81–98.
  4. Broyd SJ, van Hell HH, Beale C, et al. Acute and chronic effects of cannabinoids on human cognition—a systematic review. Biol Psychiatry.2016;79:557–567.
  5. Rubin R, etal. The role of the hipposcampus in flexible cognition and social behavior.  Front Human Neuroscience 2014;8:742.
  6. Burggren A, etal, Subregional hippocampal thickness abnormalities in older adults with a history of heavy cannabis use. Cannabis & Cannabidiol Res 2018:3.1
  7. Beale C. etal. Prolonged cannabidiol treatment effects on hippocampal subfield volumes in current cannabis users.  Cannabis and Cannabinoid Research 2018;3:1.
  8. Englund A, etal.  Cannabidiol inhibits THC-elicited paranoid symptoms and hippocampal-dependent memory impairment.  J Psychopharmacol. 2013 Jan;27(1):19-27.
  9. Hindocha C, etal. Acute effects of delta-9-tetrahydrocannabinol, cannabidiol and the combination on facial emotion recognition: a randomized, double-blind, placebo-controlled study in cannabis users.  Eur Neuropsychopharmacol 2015;25(3);325-334
  10. Haney M, etal. Oral Cannabidiol does not alter the subjective, reinforcing, or cardiovascular effects of smoked cannabis.  Neuropsychopharmacology 2016;41(8):1974-82.
  11. Bhattacharyya S, etal. Opposite effects of delta-9-tetrahydrocannabinol and cannabidiol on human brain function and psychopathology.  Neuropsychopharmacology 2010;35:764-74.




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