Originally used for breast cancer treatment to lower estrogen levels, the anabolic steroid is now more commonly used amongst body builders. Also known as Masteron, it can be used to build strength and muscle mass and can also help achieve fat loss.

WHAT ARE MULLEN'S STEPS FROM HERE?

The Newcastle playmaker was informed on Tuesday he allegedly tested positive to the drug in a routine test on November 29 last year. He has until January 31 to apply to have a B-sample tested, which usually takes around three weeks. If that comes back as positive, he will likely face the NRL's anti-doping tribunal and the case could be taken anywhere from the Administrative Appeals Tribunal to the Federal Court or the unlikely destination of the Court of Arbitration for Sport. All that could take up to one year.

WHAT KIND OF SUSPENSION COULD HE FACE IF FOUND GUILTY?

Mullen faces a four-year ban from all sport if he is found guilty - as per all other cases involving the drug in Australia. He could try and have that reduced to two years if he can prove where it came from and that he exercised utmost care to avoid ingesting it into his body. A warning is applicable if he could prove he had no fault at all in ingesting the drug.

WHAT COULD THIS MEAN FOR MULLEN?

At 29, any lengthy suspension be the end of his career. He is currently contracted until the end of 2018, meaning even a two-year ban could leave him without a club on his return. The 211-game veteran and one-time NSW State of Origin player had continued to battle hamstring injuries in recent years and was one of Newcastle' highest paid players.

WHERE DO THE KNIGHTS STAND ON IT?

A popular player at the Knights since his debut in 2005, Newcastle chief executive Matt Gidley said the club were "shocked". However he went to lengths to point out he believed Mullen had "gone outside the club and taken advice from someone".

WHAT CAN NEWCASTLE DO WITH THEIR HALVES IN 2017 AND BEYOND IF MULLEN IS SUSPENDED?

Youngsters Brock Lamb, Jaelen Feeney and Jack Cogger all partnered former NSW playmaker Trent Hodkinson in the halves in 2016. Kalyn Ponga is also set to join the club from North Queensland in 2018, and while he is seen as a fullback, he could be used as a five-eighth option. Alternatively, Newcastle could use any cash to target the likes of Jack Bird or Ben Hunt who are off-contract at the end of this year.