“Dallas Buyers Club” is a tough, grubby movie about the onset of AIDS in America, when no one knew much about it except that it was a horrifying new plague killing people. What had registered more than anything is that it seemed to be spreading fastest in two communities least likely to find allies in mainstream America: among gays and intravenous drug abusers.

Ron Woodroof was a different kind of AIDS victim – a low-living, homophobic electrician and wannabe rodeo star with a penchant for booze, coke, grungy topless joints and the kind of straight, though well-populated (threesomes, foursomes), pickup sex that one might arrange there.

He’s a good ol’ boy about whom there is little, if anything, good.

He’s played by Matthew McConaughey who lost a whopping 47 pounds for the role. When we first see McConaughey – so long infamous on talk shows and TMZ for taking his shirt off as frequently as possible to show off his six-pack – he is a thin, ravaged, very dirty-looking man with a persistent cough.

In the course of a minor medical treatment, a standard blood test reveals something that he couldn’t possibly know was coming: He has full-blown AIDS, not just incipient HIV. In the terrifying medical ignorance of the disease’s earliest days, he’s given 30 days to live.

The drug AZT – then merely being tested – is the only hope provided by mainstream American medicine. A doctor at the clinic (Jennifer Garner) is sympathetic, but is clearly professionally stricken by this rapidly growing community of suffering.

Woodroof hears about alternative medicine in Mexico. The doctor there (Griffin Dunne, barely recognizable) is barred from practicing in the States, but he’s experienced enough with AIDS treatment to know that it needs to be a complex pharmacological cocktail, not one drug that is still being tested and that, if misused, is almost as likely to kill as the disease.

At this stage, with AIDS ravaging communities so lacking in social and political clout, drug research has won out over treatment. People are dying. Drug companies are getting ready for profit.

Woodroof, then, is about the least likely activist in any cause that America could invent – a dedicated lifelong bad boy happy out on the American fringe who had, unfortunately, the best reason in the world to find treatment for a deadly plague.

With his disgraced medical guide below the Mexican border, he confounds his own medical diagnosis by not only surviving, but concocting a plan whereby other sufferers can find treatment that improves their health. He invents a “buyers club” that will dispense unapproved drugs, herbs, etc., for AIDS victims as long as they pay a flat monthly fee.

What that means is that this homophobic, would-be bull rider winds up cruising gay bars for customers (and fellow human beings in the same boat as he). He winds up with a partner, an AIDS-stricken cross-dresser named Rayon (Jared Leto) who doesn’t have the money for sexual-reassignment surgery and is, besides, unavoidably headed for personal apocalypse.

The movie has reminded people of “Erin Brockovich” in its portrait of the most accidental but effective of activists against murderous corruption.

There’s a crucial difference, though: All of the actors here are clearly going for broke. The movie could have been a toss-off, made-for-TV cable thing. I don’t think McConaughey’s loss of 47 pounds was the only indication of everyone’s commitment.

Leto, as Rayon, is similarly going for broke in the kind of androgynous role that is seldom performed as movingly as this.

That seriousness is what makes this movie so compelling. It is Dunne’s presence in the small part of the Mexican doctor that indicates where this movie is coming from. Not only has Dunne been a victim’s advocate since youth because of the murder of his sister, actress Dominique Dunne, by an old boyfriend. He revealed after the death of his father, writer Dominick Dunne, that his father had been bisexual.

Griffin Dunne had reasons to take a near-cameo role in this movie.

I suspect that without turning it into publicists’ hype, that’s probably true of this whole cast, as well as the director. They have all, no doubt, known and lost more than a few friends and colleagues to AIDS, and doing this movie in this way is one way of honoring a time that dishonored and forsook so many.

If so, well done. It’s not, I don’t think, a major movie, but the commitment of everyone in it is nothing but.

dallas buyers club

3 stars

Starring: Matthew McConaughey, Jared Leto, Jennifer Garner, Griffin Dunne

Director: Jean-Marc Vallée

Running time: 117 minutes

Rating: R for nudity, strong sexual content, language, drug use and very adult subject matter

The Lowdown: In the earliest days of AIDS, a grungy, low-living wannabe rodeo cowboy turns into a medical activist to save a community dying from ignorance, inaction and corporate corruption.