The statistics on steroid use are notoriously unreliable. According to the latest crime surveys, fewer than 70,000 people in the UK use the drug to bulk up and build muscle.
But scientists working for the government think that's probably a huge underestimate.
You get either really emotional or really horny. You can get road rage where you get really aggressive for no reason
Jack from Banbury had side effects after taking steroids
Data from health clubs and GPs' surgeries show that as many as 250,000 people could be regularly injecting or taking the drug in pill form.
Researchers say use has boomed over the last decade as young men have become more image-conscious and the drug has become more easily available.
But anabolic steroids still sit in a legal grey area. Most are treated as a Class C substance alongside ketamine, GHB and some painkillers.
Although selling or dealing the drug is illegal, possession is still allowed, party because it has a number of medical uses.
"The complicated situation regarding steroids makes it very difficult for young people to know what the law is," said Claudia Rubin at the drugs charity Release.
"More importantly, while the focus remains on law enforcement, advice about the health risks involved with taking any type of drug is largely absent."
Newsbeat spoke to 'Steve', not his real name, from Huntingdon, who's been using the drug for years to bulk up and compete in bodybuilding competitions.
"I'd been training in the gym environment but had 'plateaued' on size and strength and needed that extra boost," he said.
"I sought the right advice but it comes with hard work, nutrition, good supplementation and good sleep. It's knowing what to do it, when to do it and how to do it correctly.
Most steroids are treated as a Class C drug alongside ketamine
"Buying from the internet you are left to your own devices with no advice and no guidance. That's obviously people's choice but I know where I would rather be going."
Steve says he's been taking steroids for years and never experienced side effects. But other users have told Newsbeat about their problems with the drug.
Twenty-three-year-old Jack from Banbury said he developed side effects after starting to take steroids in his teens.
"You get either really emotional or really horny. You can get "roid rage" where you get really aggressive for no reason.
"I've lashed out at a few of my mates for the slightest thing, which I've apologised for," he told Newsbeat.
Jack also developed physical side effects including gynaecomastia (male breast enlargement), caused by the increased levels of the female hormone oestrogen in the body.
Other side effects can include needle accidents after injecting, bad reactions to the different steroids available, loss of sex drive, sterility, acne or more seriously, high cholesterol, liver damage and heart problems.
A group of drug experts led by Professor Iversen is now putting together a report for the government that could recommend tightening some of the rules around steroid use.
"There will be some debate about that," he said. "It's one option I'm sure will be considered. But if you ask for my personal view, I don't think criminalising young people is the answer."
His group's final recommendations are due before the end of the year.