Don Birnam (Ray Milland) is a writer - in theory - and an alcoholic - in indisputable fact. Coming off a bender, telling himself he's finally going to write that big novel, Don's itch to drink is palpable as his brother (Phillip Terry) helps him pack up for a restful long weekend in the country. Instead, drawn to booze with the stubbornness of a boomerang, Don ditches his brother and his long-suffering girlfriend (Jane Wymann) to gulp down several shots of whiskey at the local establishment. Don, who was uptight and irritable in the first scene, loosens up, waxes eloquent on the wonders of whiskey, and flirts with a sassy hooker who picks up johns in the bar. It's a clear and effective depiction of why drinking appeals to this insecure artist - and it will be the last such moment. Having presented the magical deliverance of the ennui-quenching rye, writer/director Billy Wilder and co-writer Charles Brackett proceed to display, in merciless detail, all the drawbacks of the addiction. Don becomes a kind of 40s Dante in reverse, descending from brief intoxicated Paradise, through a purgatorial search for satiation, and finally into the depths of DT Hell. Only his longtime lover can hope to rescue him from the depths of his own self-hatred, of which the hard drinking is both partial cause and persistent symptom.
Compulsively watchable, with its strong performances (especially from Milland, who manages to be both pleasingly theatrical and harrowingly natural), juicy dialogues and monologues, and its de facto structure. The use of a single weekend as a framework (although the filmmakers cheat a bit by using flashbacks) focuses the action and makes Don's decline from sobriety through every stage of drunkenness to suicidal withdrawal all the more effective. The Lost Weekend is a very good movie, but it isn't great - and it's one of those films which can be frustrating to watch at times, because you can sense greatness within its grasp. Though the flashbacks are effective in laying out Don's pathology and explaining his mysterious relationship to Helen (whose affection for him and patience with him initially seems unwarranted), one wishes a less artificial construct could have been found. The film is sharpest when it stays on its one-weekend timeline, and when it unfolds by keeping pace with its hero's descent. Even the flashback photography is not as precise and focused as the images of the "present" - as if Wilder and fantastic cinematographer John F. Seitz were aware that their explanatory history wasn't as strong as their demonstrative real-time. There's also an overemphasis on explaining the addiction, which is after all as much chemical as anything else, but one is tempted to forgive the frequent psychological self-analysis, as it's so artfully written.
The film was marked as "realist" at the time of its release, when it won an Oscar for Best Picture in 1945. However, "realism" is not the same as "reality" and part of the film's appeal lies in the friction between the pleasures of Hollywood style (despite its location shooting, the films falls safely within the framework of studio filmmaking) and the darkness of the subject matter. The classicism gives us an familiar frame within which to view the grim reality of alcoholism, and The Lost Weekend is all the more effective for it. Like many thematically ambitious films, it dates more than movies which may have seemed less "edgy" and "relevant" at the time - when it lectures, explains, or at times overdramatizes Don's drunkenness it can seem out of touch. Mostly, however, the movie is still stirring, evocative, and engaging. The bat in that infamous scene does look embarrassingly fake, but the set piece has a great, grisly finish which still sickens. An excellent movie, flawed but a classic.
(Incidentally, many will adjust the balance more in favor of the latter than the former - take Tony d'Ambra, curator of filmsnoir.net, with his marvellous and celebratory write-up on the movie; you should absolutely follow the link for a more in-depth view of the movie.)