Smit tested positive for clenbuterol, a banned anabolic agent, which is sometimes used as a performance enhancer to increase lean muscle mass and reduce body fat.
His A-sample, taken after Smit upset Rio Olympian Antonio Alkana at the South African Senior Championships in Potchefstroom in April, returned an adverse analytical finding.
While the tribunal panel ruled on his sanction, Athletics SA would have to decide whether it would strip Smit of his title.
Smit waived his right to have his B-sample analysed and was provisionally suspended from competing from May 25. In his submission, during the hearing, Smit admitted to taking clenbuterol to shed 2 to 3kg.
“The athlete admitted it was very negligent of him not to ask his doctor or coach, or to do some research on products,” the disciplinary panel said in its ruling.
“He stopped using the substance as the side effects got the better of him.”
Smit was subsequently given a four-year ban from May 25 and he will be eligible to compete again in May 2021.
“He is an experienced athlete and the fact that he did not make a substantial effort to find out what he was using, taking into account all the resources at his disposal, is in itself a big departure from the expected standard of behaviour of such an athlete,” read the tribunal's judgment.
“Meaning, an athlete of this profile who competes at a national level, who is aware of anti-doping rules, who was tested twice before but yet did not take any measures to ensure what he was about to use is not on the banned list.”
Smit is the second top South African athlete over the last year to test positive for a banned substance.
Discus throw ace Victor Hogan recently returned after serving a nine-month ban after testing positive for the prohibited substance methylhexaneamine.