THE BODY'S SELF-DEFENSE MECHANISMS protect it from foreign and harmful substances that ranges from the natural to unnatural to the synthetic. e.g., germs, bacteria, viruses, allergy medicine, cough syrup, cancer treatments, alcohol, beer, wine, morphine, marijuana, cocaine, opioids, etc. The body's natural defenses will always try to reduce the effects of these foreign substances at the cellular level (eg white blood cells) to the organ level(eg liver).
MORE EFFICENCY MEANS LESS HIGHS
The body's natural self-defense will be the most active on the inital encounter and then develop more efficient strategies later on. For example, OTC allergy medications work best when initially used, but later on, have no effect on allergies (eg pollens) as the body's natural self-defense has developed more efficient ways to purge the allergy medication. Similarly, the same can be said for marijuana as the initial use of pot delivers the greatest high, but the body's natural self defense will develop more efficent mechanisms to purge and reduce marijuana and it's "high" effects. (Accordingly Medical Marijuana is temporary band-aid effect on seizures and is a short lived remedy.)

Similarly, this is the same for alcohol. Over time, the body's natural self-defense will develop more efficient ways to purge alcohol and hence the "feel good" effects require more and more alcohol to be consumed to have the same initial "feel good" effects. Drinking Games are basically a measure of one's liver alcohol processing capabilities, a shallow goal in the Big Picture of Life.

This body's natural self defense mechanism of developing more efficient purging of foreign sustance like marijuana and alcohol is also true for morphine, cocaine, amphetamine, opioids, etc.

THE YIN AND YANG of POT
Yet , long time pot heads are all over the place. Some think they are getting a high, but because this "high" is physchological, their high is really a chosen, percieved state of mind as the body's more efficient natural defenses of purging has made marijuana to become like a placebo; That is, the user "thinks" marijuana gets them "high" and; hence, demands it (i.e., a addicted to pot.). But in reality, the natural defenses of the body has developed more efficient mechanisms to reduce the "high". Nevertheless, over time, the marijuana, literally "burns out" the brain's neurons and the person's ability to function in the real world is noticeable deminished. e.g. from initial so-called creativety that crashes down to laziness, depression, anxiety post-traumatic stress disorder and eventually suicide....Put another way, What goes up (the high), must also go down (the crash). Reference: See your local homeless shelter and homeless tent camp.