Mia St. John has admitted to doping throughout her career ©Getty Images

Former world champion boxer Mia St. John has admitted to doping and taking elaborate steps to cover it up during her professional career, despite never failing a test.

The 51-year-old, who enjoyed 49 wins in 61 fights between 1997 and 2016, said she took a variety of banned steroids and weight-loss substances to prepare for an estimated 20 fights.

Masking agents and "catheters with other people's urine" were used to successfully hide the cheating, she said.

The American claimed that "everyone does it [doping]" in the sport and that "everyone in boxing knows it", although her comments received a swift backlash from other fighters.

St. John had intervened on Twitter after Gennady Golovkin reportedly called Canelo Alvarez "the most unpleasant and dirtiest opponent I've ever had...dirty in the taking of substances that are prohibited and trying to blame other people" before their highly anticipated rematch next month.

Alvarez was suspended for six months after failing a test for banned steroid clenbuterol in February, which he claims to have obtained inadvertently via contaminated meat.

St. John wrote on Twitter that it was "hypocritical" for fighters to criticise Alvarez before suggesting that if they feel so strongly they should "give up the $ and don’t fight him".

She then admitted to taking banned steroids including stanozolol, nandrolone and oxandrolone during her career.

"Obviously, I'm a Canelo fan, but I hate it when other fighters put down other fighters for something we all know is rampant in boxing," St. John told the Los Angeles Times.

"I never once tested positive, and I've never told anyone this, but now that I'm retired I feel like it's okay.

"It's not right, but what I'm trying to say is that it's a vicious cycle we get caught up in. 

"You're in a gym, you're in a big camp, obviously, I was part of the biggest shows of my time.

"So when your camp is doing it, it's going around the gym, your sparring partners are doing it, you feel compelled - 'Oh my God, I have to do it' - to keep up with everybody. 

"It's a mind trick. 

"And once you're on it, it's so hard to come off because it becomes very addicting - that's what people don't know."

St. John said she was "tested many times" and "there's many methods to get around it" before claiming that "just because you didn't get caught doesn't mean you weren't doing it - it just meant you didn't get caught".

She said she was not on drugs before every bout in her career, but did not specify in which particular moments she was doping.

Mia St. John, right, pictured during a bout in 2001 ©Getty Images
Mia St. John, right, pictured during a bout in 2001 ©Getty Images

"I did my homework," she added to the Los Angeles Times. 

"They gave us a whole list of what not to do and I knew a lot of stuff I was doing was on that list. 

"I did everything I could to mask it - masking drugs, catheters with other people's urine - and then the rest is up to luck.

"I would leave the bathroom shaking, praying and sweating bullets. 

"You cross your fingers. 

"Crazy enough, I didn't get caught. 

"Some girls did and I felt so awful and ashamed, like what a hypocrite…in many ways, yes, I was protected."

Other boxers have lashed out at her following her comments.

"Sorry to inform you BUT NOT EVERYONE does it sweetie!" responded Great Britain's former cruiserweight world champion Tony Bellew on Twitter.

"Some of us former world champions actually believe in training insanely hard and having a fair fight and what will be, will be.

"It's sad and worrying that people taking PEDs [performance enhancing drugs] actually think like you do."

Former rival Christy Martin, who lost to St. John in 2012, asked: "How could you cheat knowing I had a stroke?"

Stanozolol, a synthetic steroid derived from testosterone, is the substance sprinter Ben Johnson tested positive for at the Seoul 1988 Olympic Games.

Former world champion Fernando Vargas is among boxers to have failed for the drug after he was beaten by Oscar De La Hoya in a super welterweight world title fight in 2002. 

New tests developed in recent years by scientists including former Moscow Laboratory director Grigory Rodchenkov, the main witness in the Russian doping scandal, enabled the substance to be detected in the body for a far longer period after usage.

This led to dozens of strength-based athletes in sports such as athletics and weightlifting testing positive following re-analysis of frozen samples from the Beijing 2008 and London 2012 Olympic Games.

Nandrolone, which enhances muscle mass, is the substance that former heavyweight world champion Tyson Fury failed for in 2015 while oxandrolone is another anabolic steroid which boosts muscle tissue growth.