The X Factor star revealed that he even used to inject Melanotan II - a drug developed to treat cancer patients - in an effort to keep his skin looking bronzed.
Clark bought the substance on the internet and injected himself daily for four weeks before experiencing unpleasant side effects.
"I couldn't breathe properly," the Essex-born singer told the paper. "I thought I was going to die."
Despite the scare, Clark admitted that he continued to use Melanotan II - which he claimed is not illegal to buy but is illegal to sell - for a further two months.
"I'm vain. I couldn't help myself. It was crazy," he said. "I'm a tanorexic. But I took things too far."
Clark - who also has a tanning booth in his home - explained that his addiction started in adolescence: "Growing up I got a lot of stick for being gay, fat, pasty and ginger. I thought to myself, 'Well I can't change the gay thing but everything else I can sort out'."
After he began to develop white spots on his stomach, Clark finally stopped using drugs. He is currently having regular spray tans at the five-star London hotel where the X Factor finalists are staying.
On the first of the live shows that aired last night (October 6), Gary Barlow criticised Nicole Scherzinger's decision to put the 23-year-old through, saying the panel should be "ashamed" of themselves.
Clark hit back and said that although he did not have the "best voice" in the competition, there was a "lot more to the show than the voice".
He told the panel: "This is what I want to do."
The X Factor continues tonight at 8pm.
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