I’ve only tried marijuana three times in my life and each time the “high” has been significantly less intense than the last. I am not a druggie and only did in roughly eight month intervals. Why does that happen?
If we have a cell that has a receptor for THC and other canniboids. I can understand the cell using “desensitizing” machinery like beta-arrestin or ubiquitin to remove THC receptors from the cell surface. Does this machinery work on the scale of months? years? decades? n addition, from a molecular perspective, can someone take me step-by-step on what THC does to a cell and its proteins?
Thanks 
Was the marijuana you tried three times all from the same batch? AIUI, marijuana strength can vary from batch to batch, so it’s possible you’re just getting less THC now than you used to get, not that your body is getting used to it. Anecdotally, I have friends that have been smoking pot of 20 years and they get just as high now as they ever had without having to smoke more. I remember reading somewhere that THC levels were actually increasing due to competition where pot is legal, but that may have just been conjecture.
Not my area, but yes. The first couple of times you smoke nicotine, you get a buzz. You never get that buzz back again, even years later. Same for opioids. People who have used opioids are resistant to medical anasthesia and analgesia for a long time after.
No citations. Just an opinion.
(people continue to use acetaminophen/paracetamol (which is a canaboid) for years: it’s not like it ceases to have any effect. And marijuana is a mixture of psychoactive drugs).
@dolphinboy — you working your way through wrapping up some unfinished SD business?
The poster you are addressing left about seven years ago.