Originally billed as a "tribal love rock musical", the arrival of Hair in 1967 marked a revolution in musical theatre history, bringing the spirit of youth and a contemporary rock idiom to a genre that had been long languishing in the musical as well as theatrical past. This was a show that spoke to the young generation of the day, and addressed some of the most urgent concerns that preoccupied them, like Vietnam and the protest movement. But as a revival at the Old Vic demonstrated in 1993, the show had by then itself become a historic relic, as quaint and as dated as Show Boat or Oklahoma!.

Now the Gate has reclaimed it from history and reinvigorated it as a show for today in every way. Under the direction of Daniel Kramer, this is surely one of the most radical makeovers of an old musical I have ever seen, hurtling it forwards from the late 1960s right into the embrace of the 21st century.

As Hair wilfully scandalises and thrills in equal measure, Kramer has, in collaboration with the original authors James Rado (who co-wrote the book and lyrics with Gerome Ragni) and Galt MacDermot (who composed the music), played loose with the original text and score, re-scripting, updating and re-arranging it throughout.

A musical about "tribal love" has, in the process, become a far grittier, hard-edged story of contemporary hatreds, with images torn from newspapers, such as the famous torture scenes from Abu Ghraib prison. It is also a story of the terrors of youth, and how confusing trying to make sense of the world might be. Especially now, when the ideals of free love that the show so famously espoused could mean death (the spectre of HIV hangs heavy over the show, one actor even has the initials tattooed to his chest), and everyone is immersed in a heavy drug culture.

Kramer, who is in his mid-20s and was therefore not even born when Hair was first staged, has done what all brilliant directors do - namely interrogated it for fresh meaning through his own eyes and times. The show proves both resilient and responsive to his vision, fuelled as it is by some truly great songs and a production galvanised by Ann Yee's kinetic choreography that explodes across the wide stage the Gate has been newly configured to create.

The brilliant ensemble company includes stand-out turns from recent RADA graduate Charles Aitken as Claude, stumbling through life on Prozac, Kevin Wathen, Joanna Ampil and Golda Rosheuvel.

While Hair was originally notorious for introducing full-frontal nudity to the British stage - the original London production opened the day after stage censorship was abolished - this time things get downright raunchy. You might want to leave your hang-ups at the door, but this production is otherwise Prozac for the soul.

- Mark Shenton