Heroin kills. Smoking kills. Alcohol kills. These things we know, even as we reach for a dram, a puff or a fix. The odd status of such warnings, these axioms of addiction, is what Joanne Tatham and Tom O'Sullivan explore in an astonishing, epic sculptural installation. Three-dimensional letters, 6m high, stretching right across the vast main space at Tramway, spell out their message (heroin kills) in monumental form, one that is both shocking and playful.

What play there is comes from the references to other famous groups of letters - those that spell out Monty Python and Hollywood, the black letters saying "The Ramones", held by the group in a photograph. It's also about the scale of the piece, and its dour monochrome of white walls and coal-black letters, echoing the atmosphere of those 1980s Don't Die of Ignorance health warnings about HIV that featured tombstones and were lit like a morgue.

But HK is more than smart intertextual references. Our first sight is of the message back to front, and in its stark beauty, with chinks of light spilling through the gaps in the letters, the slogan forms a mirror to Glasgow's vexed relationship with smack. At the heart of one of its key former industrial spaces, we cannot miss the impact of the message; it's a fact of life in the post-industrial reality just beyond the gallery. This is where the shock kicks in.

"Heroin kills" are not the only words in this exhibition, though. Pasted on to noticeboards in the foyer, you will find, in comparatively tiny lettering, testimonies of former addicts and those who are still struggling with addiction. And it's in the space between the two - these sad tales, and the giant, meaninglessly obvious slogan - that Tatham and O'Sullivan's interest lies. Their sculpture suggests that, somewhere between the individual struggle with drugs and the hysteria of much of the media's coverage of heroin, perhaps other words and other stories lie.

· Until January 20. Details: 0141-422 2023.