She went in and swallowed all the pills and capsules in the medicine cabinet and then washed them down with a bottle of gin. (1.4)
We get this information rather early in the story. It's the first mention of drugs and alcohol, and it connects them with desperation. The line is important as well in understanding that the narrator's wife, who tried to kill herself during her first marriage, might be in a vulnerable position even now.
Right then my wife filled me in with more details than I cared to know. I made a drink and sat at the table to listen. (1.14)
This is the first drink of the evening. The narrator is using alcohol to tolerate things he doesn't want to hear from his wife.
We had us two or three more drinks while they talked about the major things that had come to pass for them in the past ten years. (1.45)
They actually have about 22 drinks over the course of the evening, or about seven each, with an extra one for the narrator. Since nobody seems to get too crazy, this suggests that they are all fairly used to alcohol. It also means that Robert and the narrator were intoxicated when they had their big experience.
Every night I smoked dope and stayed up as long as I could before I fell asleep. (2.29)
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?
I reached for my glass, but it was empty. I tried to remember what I could remember. (3.7)
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.