Cathedral Drugs and Alcohol Quotes

It's pretty clear from this line that the narrator is a habitual marijuana user. He doesn't seem too happy about this fact. Yet, he and Robert are probably high when they draw the cathedral, which is a positive experience by all accounts. Is the story making some point about drugs and alcohol? If so, what?

And that's the end of the drinking in "Cathedral." When the narrator begins trying to "remember" and describe the cathedral, he forgets all about drinking.