I find Storm Crow's endocannabinoid deficiency explanation very plausible. But, to be honest, I still find the cannabinoid receptor "warm up" theory plausible, too, especially after talking to my med school neuroscience professor about this same topic. Yes, we have an endocannabinoid system inherent in our bodies and brains that is ready to respond to the endocannabinoids we get in, say breast milk, to name some of the first ingested endocannabinoids. But my professor's theory, which he said was borne out of a similar response by some people to opioids, is that externally ingested/smoked cannabinoids may still elicit a different response--or require a warm-up period--from the way natural endocannabinoids affect those inherent receptors. The same thing happens, he says, to people's opioid receptors, which are inherent in our brains and bodies us but which, in some, respond differently to ingestion of external natural or synthetic opioids, depending on how well they've been acclimated.

So I'm still going to buy into the delayed-awakening receptor theory. I was one of those people who smoked and smoked weed and got no response until I'd done it about 10 times. (A less persistent type would have given up!) I was smoking and inhaling correctly. I'd learned how to do that with cigarettes, which I thought were glamorous in those days. I simply didn't get high until I'd had some repeated exposure to external cannabinoids.