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Marijuana is perhaps the most commonly used illegal drug in this country with over 5 million persons noting weekly use or more.  What is more, the potency of marijuana is increasing which will only serve to increase its abuse liability.

Marijuana is both eaten and smoked.  The active component, delta 9-THC, is among a group of compounds known as cannabinoids and will be referred to as cannabis.  Cannabis has an affinity to affect certain areas of the brain.

It works to increase dopamine in the Nucleus Accumbens which is the effect responsible for its' euphoria.  There are at least two mechanisms by which this is accomplished.  First, it leads to a release of endorphins.  Endorphins, the brains's natural opiates, are themselves euphoric.  In addition the endorphin release secondarily leads to dopamine release.   The second mechanism is also a little roundabout.  Cannabis will lead to increased glutamate in the Nucleus Accumbens which then also increases dopamine release.

The lateral hypothalamus is responsible for stimulating hunger.  Nerves which begin here release a neurotransmitter called Orexin into the Nucleus Accumbens.  This may be the most significant driver of our appetite.  There are cannabinoid receptors throughout the hypothalamus including the lateral hypothalamus.  Here it may intensify the release of Orexin. This is one major component of why we get the munchies after we use marijuana.

Other area affected by cannabis include the cerebellum (involved in the coordination of movement) as well as the hippocampus (involved in the formation of new memories).   Memory formation and coordination are impaired during cannabis intoxication.  One last area affected is the prefrontal cortex, the executive part of the brain where complex behaviors are either initiated or inhibited.  This area is also impaired 

Receptors have been identified for THC.  Additionally, a naturally occurring molecule that stimulates this receptor has also been identified.  It has been named Anandamide.  Research is ongoing to understand the physiologic function of Anandamide.  One area where it has a role is in pain perception.  Stimulation reduces pain.  There is a role for cannabinoids in pain management.  It is also seen outside of the central nervos system where it is involved with sugar and fat metabolism, liver, pancreas and muscle functions.

Cannabis users will experience a euphoria and a state of relaxation.(dopamine and opioid effects)  There are visual perception abnormalities, time perception abnormalities and intellectual function impairment.  All these combine to make the intoxicated person an unsafe operator of motor vehicles. 

In addition, the ability to learn new information is impaired.  The long duration of marijuana in the body makes this last impairment more of a concern as  cognitive defects can last relatively long periods of time.  One important question is how long such cognitive effects last.

Several years ago. a study was done to answer this question.  Volunteers, who were clean of marijuana were recruited and a functional MRI was done.  A normal pattern of activity was seen.  They were then given marijuana and a test was repeated almost immediately.  The prefrontal cortex was seen to be less active consistent with cognitive impairment.  24 hours later, there were still deficits in the functioning of this area.  It takes a long time to become cognitively 100%

I often see patients are much sharper months after stopping marijuana.  Many users protest that they can function well and perform at a high level while using marijuana.  What they do not realize is that without marijuana, they would be doing even better.   If a person has chosen an occupation that requires repetitive behavior, marijuana may not seemingly affect them.  However, if they need to be at their best, than they will see the difference.  How many people will let a brain surgeon operate on them who is intoxicated with marijuana?

Marijuana use can cause respiratory problems similar to that of tobacco.  It is not healthy to inhale smoke.  Smoke had a lot of toxic chemicals including carbon monoxide, formaldehyde and free radicals.  These are absorbed where they contribute to the development of arteriosclerosis and cancer.

Marijuana decreases testosterone and may  decrease libido.  It reduces sperm count and sperm activity.  It causes menstrual irregularities, through a variety of mechanisms, and can even cause the breast to secrete milk.  Children born to mothers using marijuana tend to be underweight with increased irritability and shakes.  Cannabis has also been shown to alter immune function.  

There is an associated withdrawal syndrome when the drug is stopped which serves to perpetuate its use. (See “Is marijuana addictive”) In addition, any time a person spends a lot of time intoxicated, the effects on their  work  and interpersonal relations can be significant.  

There has been a lot of political rhetoric over the use of marijuana lately.  I agree that there are some medical conditions where the uses of marijuana may be warranted; however, let’s not overlook the negative effects of the drug when we have our discussions.  There have been studies that show that the use of marijuana goes down when people think of it as a dangerous drug.  Unfortunately, over the last few years, the perception that the drug is completely safe has been increasing.  We need to change that.  

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S. Wasser
May 10, 1997
revised 12/5/10