This Is Your Brain on Drugs: The Science of Cannabis

Whenever I hear talk of marijuana legalization on this campus, I am a little dismayed. This is not because I have a particular opinion that is challenged by my peers, but because I tend to only hear one or two arguments surrounding the issue. 

One is sociopolitical, involving discussions about taxation, curbing incentives for illegal trade, and ending a War on Drugs that disproportionately targets racial minorities and those in poverty. The other is pseudo-scientific, and usually compares using cannabis to using alcohol or tobacco, or points out that smoking marijuana is not physically addictive. 

While these arguments are certainly relevant to the discussion, I can’t help but feel like something’s missing: the actual science. How does the drug act in the brain? What are the short-term and long-term effects? 

As it turns out, the system that THC, the main active compound in marijuana, affects in the brain is fascinating. THC takes advantage of what is called the endocannabinoid system, endo- meaning “internal” and -cannabinoid meaning “cannabis-like.” When a user smokes marijuana, THC is released as a vapor (along with a host of other hydrocarbon gases, also known as smoke) and reaches the bloodstream directly through the lungs. 

Its chemical properties allow it to quickly enter the brain, where it acts like a huge dose of our naturally produced endocannabinoids. Since it is chemically similar to these physiological neurotransmitters, it activates all the receptors that would be activated by an endocannabinoid. 

These are known as CB1 receptors, and they are extraordinarily unusual because they lie on what is known as the pre-synaptic cell and not the post-synaptic cell. The vast majority of synapses, or junctions between neurons, are anterograde, meaning the pre-synaptic (before the synapse) cell releases a chemical that either activates the post-synaptic (after the synapse) cell.

When endocannabinoids act on the brain they, in a sense, send information in the retrograde direction—backward—since the CB1 receptor is found on the pre-synaptic cell.

Now, that isn’t as crazy as you may think. Your brain doesn’t work backward every time you smoke weed. The activation of CB1 receptors has one major neurochemical outcome: It makes the pre-synaptic cell less likely to release its neurotransmitters. That is, it selectively turns down the activity of any neuron that contains these receptors.

But what happens psychologically when somebody smokes cannabis? Perhaps the most well-established effect is the impairment of memory encoding, consolidation, and recall—that is, the formation of new memories, the decisions as to which memories are important, and the remembering of old memories. One caveat is that this deficit only applies to remembering things that happened during cannabis intoxication. 

Another effect is hunger activation, which occurs by increasing activity in the hypothalamus, a walnut-sized nucleus of brain tissue that controls automatic body functions like temperature, thirst, hunger, and sleep.

In 2006, the hunger-inducing effects of CB1 receptors were utilized to create a European weight-loss wonder drug that blocked CB1 receptors from being activated. The drug, Rimonabant, essentially had the opposite effects of THC, including a down-regulation of hunger. Interestingly, it was pulled from the market by the EU by 2009, citing significantly higher rates of suicide and severe anxiety and depression among Rimonabant users.

Though science is mostly out on the role of the endocannabinoid system in our brain, the Rimonabant story illustrates at least one important function: the reduction of anxiety and depression. But consistent overactivation of the system, which is what happens with heavy, chronic marijuana use, does not necessarily decrease depression and anxiety. In fact, it may have the opposite effect.

This is because of a phenomenon called tolerance. Tolerance is the brain’s response to any drug that acts on it. Let’s say someone named “Blunt-Smokin’ Betty” smokes marijuana every day. Over time, Betty’s brain will start undergoing changes that reverse what the daily THC is doing in her brain. Since cannabis intoxication causes overactivation of CB1 receptors, her brain starts getting rid of these receptors so the system isn’t overloaded every time she lights up a blunt. 

Eventually, Betty does not feel the same subjective high by smoking the same amount, so she smokes more and more, which just causes the brain to even further counteract the effects of THC.

But what happens if Betty were to stop smoking? Unfortunately, she might look like someone taking Rimonabant, because her brain has become so accustomed to the CB1 overactivation by her smoking that it is not conditioned to function normally. Evidence of this effect can be seen in information processing tasks, or tasks that require a subject to gather and manipulate information. A study by Kelleher et al. in 2004 demonstrated that chronic users abstinent from cannabis showed decreased information processing speeds compared to control subjects, but these abilities were recovered once the chronic users smoked marijuana. 

Thus, when someone tells you that you cannot be addicted to marijuana, do not believe them. While it’s true that physical addiction like that caused by alcohol does not result from chronic cannabis use, dependence on marijuana (to process information normally or maintain a good mood, for example) is entirely possible. An estimated four million Americans meet the criteria for psychological dependence on marijuana, which is double the number from 2001. 

Nothing that I have written here should affect the sociopolitical arguments surrounding marijuana legalization, but hopefully I have shed some light on the people who start talking ‘science’ when debating this issue. Though a semester’s worth of columns could probably be written about the issue, my main goal here is simply that you should keep the effects of cannabis in mind. I’ve found that they are often overlooked because marijuana is considered safe. Though this is true in that using it will not kill you, it doesn’t necessarily translate to complete psychological, physiological, and mental health. 

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