Viagra brings new vitality to late night jokes - for now.

Sipowicz (Dennis Franz) used it after having prostate surgery on NYPD Blue. Paul (Paul Reiser) used it on a dare on Mad About You. Mayor Winston (Barry Bostwick) used it after having trouble getting an, er, election on Spin City. And late-night comics use it as an all-purpose punchline. Why does Viagra keep popping up on TV?

”It goes right to the heart of people’s real concerns of aging and adequacy and intimacy,” says Jonathan Groff, head writer for Late Night With Conan O’Brien, which has featured its fair share of Viagra gags (e.g., ”Viagra is being prescribed 40,000 times a day…. Experts expect that number to eventually go down, but then to go back up again after a few minutes of cuddling”). ”It gave us a clinical, FDA-approved reason to do penis jokes,” says Groff. Adds Spin City cocreator Bill Lawrence: ”It’s one of the easiest materials ever for comedy — you can’t get an erection, you take a drug, you suddenly have one all day, and you see things blue. For comedy writers, that’s like a gold mine.”

As recently as a few years ago, this material couldn’t have been mined in late night, much less during prime time. But as the networks strive to compete with increasingly permissive cable programs, censorship standards have loosened to the point where Paul Reiser can walk around fully aroused at 8 p.m. — what used to be called the family hour.

Of course, the fact that Ed Bradley discussed the state of the presidential penis an hour earlier on 60 Minutes makes this seem a little less shocking. Bob Dole’s admission that he had been one of the drug’s initial test subjects also unleashed a torrent of TV one-liners. ”Elizabeth Dole was on the Today show promoting her new book, The Horrors of Viagra,” quipped Saturday Night Live‘s Colin Quinn. The good-humored former senator joined in the fun, reading a Top Ten list of ways the country would be different if he were President on Late Show With David Letterman that included ”Viagra to be served at all state dinners.”

But as demand for the drug has diminished, we may be seeing the first stirrings of a Viagra backlash. Chicago Hope recently aired an episode about the medication’s dangers for heart patients; Spin City doesn’t plan to extend the mayor’s impotence plotline (”It was just a cheap, one-time joke,” cracks Lawrence); and Groff says Late Night has cut back on its Viagra jokes. ”For about two weeks in 1988, you could just mention Dan Quayle’s name and get a laugh, and that’s what we found with Viagra,” he says. ”But it was like eating too much pistachio ice cream — after two weeks, you couldn’t touch it again.”

Yet perhaps because CBS has the oldest audience, Letterman continues to milk laughs out of the drug, which he insists on pronouncing Vee-AH-grah instead of the more common Vie-AAH-gra. (”There’s some dispute about how to say it,” offers Groff. ”But there is the nice irony of it rhyming with Niagara and the idea of cascading water and honeymoons.”) Any elderly celebrity seems fair game for Dave to link with the drug. His latest target: ”John Glenn is going to find out what happens when you mix Tang with Viagra.”