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.
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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'."
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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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