Sam Chalmers describes taking prohibited substances as the "worst mistake of my life" as he returns from a two-year ban.
The son of former international Craig Chalmers tested positive for two anabolic steroids at a Scotland Under-20 training session in May 2013.
"Life's been pretty tough," the 21-year-old told BBC Radio 5 live.
"It was my own stupid mistake but to put that in my body was the worst mistake of my life."
Chalmers is now attempting to rebuild his career in Australia with Sydney club Southern Districts.
Discussing the issue for the first time since his ban was announced in September 2013, Chalmers revealed the substances he took did not enhance his performance, but instead made him ill.
"I was in the gym with a few of my friends and they were taking a supplement," he said. "I didn't know much about it as there's so many things on the market. I took this supplement without looking into it.
"I didn't take an illegal substance, but it's illegal in rugby. That was the problem. Striving to get into the professional game and having that taken away from you. It's a nightmare.
"The drug had an adverse effect. It made me feel ill because I'm a type-one diabetic. I didn't receive any gains from it at all. Two years of playing the game I love has been taken away from me.
"When I was tested, they started asking me about what supplements I was taking and I thought maybe it was illegal. I didn't know. I hadn't even thought about what I put in my body.
"I broke down when I found out. I got in touch with my dad and he was great with me and told me not to panic.
"It's been a long two years but I'm happy to be back training in Sydney."
Chalmers has spent his time away from the game warning others not to follow his bad example.
"From the start, I came out and held my hands up," he added. "Nobody shoved it down my throat. I didn't shift the blame to my friends. I've now educated others not to make the same mistake as me. It was the right way to go about it.
"Hopefully what I've done with my educational videos and talks is to not let other people make the same mistake.
"You need to know everything you put in your body. Education will be the key for young athletes.
"There's a lot of pressure. Coaches are looking for big, powerful players but you also need small guys with speed. I'd just say to the smaller players that they will catch up with everyone else in the end. Don't do what I did."