Steroid use may be more than twice as common as official figures suggest, a leading expert has told the BBC.
Steroids are used to give a muscular physique
According to the British Crime Survey there are 42,000 regular anabolic steroid users in the UK.
Drugs expert Jim McVeigh said there could be as many as 100,000. "Basically we're looking at numbers being on a par with heroin users," he added.
One treatment centre in Merseyside reports that steroid use has rocketed in the last three years.
Staff now treat four new steroid users for every new heroin user - a reversal of the situation in 2004. There is a particular problem with users aged under 25.
Nurse Deborah Jones, who works at the harm reduction centre in Wirral, says steroid use has increased particularly among the under 25s.
Mr McVeigh, of Liverpool John Moores University, insists the problem is hidden because people do not admit to using steroids.
"At any one time in Liverpool there are approximately 1,000 anabolic steroid users - nationally we're looking at over 100,000," he told BBC Radio Five Live.
Every month, the Wirral centre sees about 21 users aged under 25, and the youngest patient is just 16.
Ms Jones says the use among younger people is growing as more and more strive for the "perfect body".
"It's all about being big, muscular, toned, and they can gain that much quicker using steroids than they ever can working out," she says.
"It does take over. They want to have the rippling six pack with the golden body, but most of them end up as the Arnold Schwarzenegger - that's what they see as success."
She likens steroid users to anorexia sufferers in that, regardless of their true size, they still see themselves as "tiny, scrawny, weedy".
Ms Jones also says steroids are much easier to obtain now via the internet and mainstream gyms.
"Parents will pay for gym subscriptions because they don't want them on the streets. They see it as the healthier option, but it can expose them to the steroid culture."
And the gyms themselves, she claims, will not accept there is a problem.
"if you tackled any of the management they would tell you categorically it doesn't go on in their place."
Steroid users are at risk from a range of health complications, including liver damage, high cholesterol and stroke, as well as life-threatening infections like HIV and hepatitis.
Younger users may also suffer from acne, extreme mood swings, depression and a lack of sex drive.
Another unwanted side effect is gynecomastia - abnormal growth of male breast tissue - because of hormonal changes.
Ms Jones says many do not accept the risks: "In their perceptions, they have very healthy lifestyles.
"They exercise regularly, they eat healthily, they're very conscious about what they put in their bodies - a lot of them won't smoke or have alcohol."
Younger users could be at added risk because of a growing enthusiasm for steroids designed for animals.
"They presume that if it's for an animal it will be much stronger and therefore it will enhance what they want in terms of strength and muscle mass much quicker," Ms Jones added.
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