A Six-Day Cycle
Because it's set over a long weekend, The Lost Weekend has an easily definable narrative structure: that of a long weekend.
Within this structure, however, there's a notable use of cycles and repeating plot points that allude to the nature of the cycle of addiction.
Basically, we're watching Don from the moment he wakes up until the moment he goes to sleep. There are some flashbacks, true, but they're depicted as stories Don is telling, so they don't diverge from this structure. What's more, there are a few jumps in time, but those only happen to us when they happen to Don as well.
As pointed out our Symbols section, there are a bunch of circular aspects to the film's plot that reflect the "cycle of addiction." For example, the closing and opening scenes are mirror images of each other—while the opening scene features Don telling Wick to find his typewriter so he can secretly locate his booze, the closing scene has Helen telling Don to find her a coat so she can secretly locate his gun. What's more, the closing shot of the movie is identical to the opening shot, only reversed.
These repeated but slightly altered plot points show that Don has broken the cycle, even though it continues to haunt him. Now, this ain't exactly Memento-level narrative deconstruction, but The Lost Weekend has a lot more chops than meets the eye.