Lessing, whose works include “The Golden Notebook” and “The Good Terrorist”, said she spends most of her time now being photographed and giving interviews.
The 88-year-old was awarded the Nobel in 2007 and at the time said it was “astonishing and amazing” to receive the honour.
Asked about her writing on BBC radio, she said: “It has stopped, I don’t have any energy any more.
“This is why I keep telling anyone younger than me, ‘don’t imagine you’ll have it forever.’
“Use it while you’ve got it because it’ll go, it’s sliding away like water down a plughole.”
She added that she had been in constant demand since her Nobel award.
“All I do is give interviews and spend time being photographed,” she said.
The BBC released extracts from the interview with Lessing, which is due to be broadcast on Radio 4 Monday, on its website Sunday.
The author was born in Iran but her British family moved to what was then Rhodesia, now Zimbabwe, when she was young. Lessing moved to London when she was 30.
Her most recent novel is “Alfred and Emily”, which she says will be her last.