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← Is marijuana bad for your brain? - Anees Bahji

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Showing Revision 2 created 01/10/2020 by lauren mcalpine .

  1. In 1970,
  2. marijuana was classified
    as a schedule 1 drug in the United States:
  3. the strictest designation possible,
  4. meaning it was completely illegal
    and had no recognized medical uses.
  5. For decades, this view persisted
  6. and set back research
    on the drug's mechanisms and effects.
  7. Today, marijuana’s therapeutic benefits
    are widely acknowledged,
  8. and some nations
    have legalized medical use
  9. or are moving in that direction.
  10. But a growing recognition
    for marijuana’s medical value
  11. doesn’t answer the question:
  12. is recreational marijuana use
    bad for your brain?
  13. Marijuana acts
    on the body’s cannabinoid system,

  14. which has receptors
    all over the brain and body.
  15. Molecules native to the body,
    called endocannabinoids,
  16. also act on these receptors.
  17. We don’t totally understand
    the cannabinoid system,
  18. but it has one feature
    that provides a big clue to its function.
  19. Most neurotransmitters
    travel from one neuron to the next
  20. through a synapse to propagate a message.
  21. But endocannabinoids
    travel in the opposite direction.
  22. When a message passes
    from the one neuron to the next,
  23. the receiving neuron
    releases endocannabinoids.
  24. Those endocannabinoids
    travel backward
  25. to influence the sending neuron—
  26. essentially giving it feedback
    from the receiving neuron.
  27. This leads scientists
    to believe that the endocannabinoid system
  28. serves primarily
    to modulate other kinds of signals—
  29. amplifying some and diminishing others.
  30. Feedback from endocannabinoids
    slows down rates of neural signaling.

  31. That doesn’t necessarily mean
  32. it slows down behavior
    or perception, though.
  33. For example,
    slowing down a signal that inhibits smell
  34. could actually make smells more intense.
  35. Marijuana contains
    two main active compounds,

  36. tetrahydrocannabinol or THC,
    and cannabidiol, or CBD.
  37. THC is thought to be primarily responsible
    for marijuana’s psychoactive effects
  38. on behavior, cognition, and perception,
  39. while CBD is responsible
    for the non-psychoactive effects.
  40. Like endocannabinoids,
  41. THC slows down signaling
    by binding to cannabinoid receptors.
  42. But it binds to receptors
    all over this sprawling, diffuse system
  43. at once,
  44. whereas endocannabinoids
    are released in a specific place
  45. in response to a specific stimulus.
  46. This widespread activity
    coupled with the fact

  47. that the cannabinoid system
    indirectly affects many other systems,
  48. means that each person’s
    particular brain chemistry, genetics,
  49. and previous life experience
  50. largely determine
    how they experience the drug.
  51. That’s true much more so with marijuana
    than with other drugs
  52. that produce their effects
    through one or a few specific pathways.
  53. So the harmful effects, if any,
    vary considerably from person to person.
  54. And while we don’t know
    how exactly how marijuana
  55. produces specific harmful effects,
  56. there are clear risk factors
    that can increase peoples’ likelihood
  57. of experiencing them.
  58. The clearest risk factor is age.

  59. In people younger than 25,
  60. cannabinoid receptors
    are more concentrated in the white matter
  61. than in people over 25.
  62. The white matter
    is involved in communication,
  63. learning, memory, and emotions.
  64. Frequent marijuana use
  65. can disrupt the development
    of white matter tracts,
  66. and also affect the brain’s ability
    to grow new connections.
  67. This may damage long-term learning ability
    and problem solving.
  68. For now, it’s unclear
    how severe this damage can be
  69. or whether it’s reversible.
  70. And even among young people,
  71. the risk is higher the younger someone is—
  72. much higher for a 15 year old
    than a 22 year old, for instance.
  73. Marijuana can also cause hallucinations
    or paranoid delusions.

  74. Known as marijuana-induced psychosis,
  75. these symptoms usually subside
    when a person stops using marijuana.
  76. But in rare cases,
    psychosis doesn’t subside,
  77. instead unmasking
    a persistent psychotic disorder.
  78. A family history of psychotic disorders,
    like schizophrenia,
  79. is the clearest, though not the only,
    risk factor for this effect.
  80. Marijuana-induced psychosis
    is also more common among young adults,
  81. though it’s worth noting
    that psychotic disorders
  82. usually surface in this age range anyway.
  83. What’s unclear in these cases
    is whether the psychotic disorder
  84. would have appeared
    without marijuana use—
  85. whether marijuana use triggers it early,
  86. is a catalyst for a tipping point
    that wouldn’t have been crossed otherwise,
  87. or whether the reaction
    to marijuana is merely an indication
  88. of an underlying disorder.
  89. In all likelihood, marijuana’s role
    varies from person to person.
  90. At any age, as with many other drugs,

  91. the brain and body
  92. become less sensitive
    to marijuana after repeated uses,
  93. meaning it takes more
    to achieve the same effects.
  94. Fortunately, unlike many other drugs,
  95. there’s no risk of fatal overdose
    from marijuana,
  96. and even heavy use
    doesn’t lead to debilitating
  97. or life-threatening
    withdrawal symptoms if use stops.
  98. There are more subtle forms
    of marijuana withdrawal, though,
  99. including sleep disturbances,
    irritability, and depressed mood,
  100. which pass
    within a few weeks of stopping use.
  101. So is marijuana bad for your brain?

  102. It depends who you are.
  103. But while some risk factors
    are easy to identify,
  104. others aren’t well understood—
  105. which means there’s still some possibility
    of experiencing negative effects,
  106. even if you don’t have
    any of the known risk factors.