Medics were called to the theatre as scenes of mutilation unfolded on stage in Katie Mitchell”s production of Cleansed, written by Sarah Kane.
Up to 40 others have walked out in the first week of previews disgusted by characters being electrocuted and force fed.
Written by the late Sarah Kane, the play set in a hellish prison sees characters are electrocuted, raped, violently assaulted, force fed and forced to undergo a sex change.
The horror continues with incest, murder, war, drugs and a tongue being ripped out.
Arts and culture writer Victoria Sadler, who watched a preview performance, said: “It”s a deliberately provocative play and it gets right in there with scenes of protracted torture and violence.
“Walkouts were inevitable and they started about 20 to 25 minutes in once people realised it was going to be sustained and deliberately graphic.
“You could tell a couple of people left because they couldn”t cope.
“The guy who fainted 30 minutes in, he was on a date and they had to put the lights up to get him out.
“It”s easily the most violent thing you can sit through in a theatre and I think there were a core of people leaving because they felt it was just trying to shock.
“The theatre warns there will be graphic content but we live in an era when people read that and will think of Game of Thrones, it”s almost enticing.”
The production is due to run until May 5 and its extreme content has seen five people require medical attention during six performances between February 16 and 22.
Cleansed, first performed at at the Royal Court Theatre in 1998, two years before a 28-year-old Kane hanged herself, is making its debut at the National Theatre.
Known as one of Britain”s most influential playwrights, Kane”s other works include Blasted- a play which includes, rape, violence and a soldier ripping out a man”s eyeballs before eating them- Phaedra”s Love and Crave.
The National Theatre said: “During the preview period there were five instances of people fainting and 40 people leaving the auditorium. At no point were any of the performances stopped.”