Clenbuterol is used to help burn fat, and by asthma sufferers. It also promotes increased stamina in athletes.
The 33-year-old was first suspended in August when the findings were made public.
Jantjies subsequently moved for his legal team to instruct a B-sample to be tested, which has now also come back positive for Clenbuterol.
Left out of Rugby World Cup squad
The veteran flyhalf did not make the Springboks Rugby World Cup squad last year, and said he was alerted by the failed doping test earlier in August.
Jantjies released a statement at the time: “It with no small amount of shock and sadness that I have to inform you that I received notification earlier this month, from the South African Institute for Drug-Free Sport, that a urine sample that I had provided to them in June 2023, returned a positive test for a banned substance, Clenbuterol.
“I have instructed legal representation to assist me in determining the source of the prohibited substance and I have instructed them to ask for my B Sample to be tested and to launch an inquiry into the possible causes for the positive test.”
Despite testing positive, Jantjies maintained he did not intentionally take the banned substance.
In the latter years of his career, however, he was no stranger to controversy.
In September 2022, reports of an affair with Bok dietician Zeenat Simjee emerged at a guest house in Nelspruit ahead of the Rugby Championship clash against the All Blacks on August 6. It was reported that a guest complained about the noise coming from the room of Jantjies to which he allegedly responded “Do you know who I am?”
Following the incident, speculation was rife about his future as a Bok, though SA Rugby said Jantjies did not breach any team protocol, but confirmed they were investigating the incident.