Channel 4 has defended its reality show Shattered after a pressure group said it was exploiting its participants.
The Shattered "laboratory" in east London
It comes as one contestant, 21-year-old student Lucy, left the show - in which contestants have to stay awake for a week - after talks with psychologists.
Mediawatch UK director John Beyer said it "beggared belief" that the network had approved the show.
But Channel 4 said it was safeguarding contestants' safety by using ethics advisers and employing medical staff.
The series started on Sunday with 10 contestants competing to stay awake in a "laboratory" in Wapping, east London to win up to £100,000.
Mr Beyer said a public service broadcaster like Channel 4 should not be transmitting a programme like Shattered.
"To use members of the public in this kind of environment is not an appropriate format," he told BBC News Online.
Liberal Democrats culture spokesman Don Foster called the programme "reality TV gone mad, reminiscent of the degrading American dance marathons of the Depression".
But a Channel 4 spokeswoman denied the show's contestants were being exploited.
"We've got an ethics committee which is completely independent to advise the programme makers, and all the participants have had meetings with doctors and pyschologists, who are always available if they need them," she said.
Contestant Lucy left the programme on Tuesday
She also defended a challenge featured in the programme, which featured contestants having to work their way through a series of doors, some of which had handles which gave them an electric shock.
Ethics committee member Trisha Macnair, writing in Tuesday's Guardian newspaper, had said the panel had vetoed the use of door handles which gave electric shocks in the programme.
"We felt this could cause fear and unnecessary suffering," she wrote in the newspaper.
But the spokeswoman said: "There were lots of variations on the electric shock challenge Trisha mentioned in her piece, and the one she mentioned was quite an extreme version of it.
"The one we used gave off an extremely mild electric pulse, which was not harmful."
Preliminary audience figures show 1.8 million people saw both Sunday's launch of the programme, and Monday night's second instalment.
By Tuesday afternoon, Channel 4 said it had received "less than 10" complaints about the series, while TV watchdog Ofcom said it had received eight complaints.
Eight of the original 10 remained on Tuesday morning, following the evictions of Birmingham fitness instructor Salma, 33, and former air hostess Ellen, 28, from Bishop's Stortford, who were judged to have performed badly in the show's challenges.
But their numbers fell further on Tuesday afternoon when north London student Lucy, 21, left following discussions with psychologists.
A Channel 4 spokeswoman said: "Lucy did have a great time and loved all the people that were taking part
and she wanted to leave with fond memories."