And although Wannenburg was never tested positive for drugs, the South African forward decided a fresh challenge would be beneficial to his career.
"When the story came out I spoke to my parents and decided to face the issues, to be honest about it," said Wannenburg, who was released by the Bulls after the end of the Super 14 campaign.
"It was tough [decision] but I needed a new challenge and so that made it a bit easier.
"To be honest, I'm not overly familiar with the Magners League, we don't get many of those matches on television in South Africa but we do see some of the Heineken Cup and that was a big draw, to be able to play in the that competition.
"It's an exciting time to be part of Ulster Rugby. I've got plenty of experience gained over the past few years and I'd hope to be able to share that with some of the younger players in the Ulster Squad and be part of building an even stronger team for the future.
"I grew up on a farm and even though I've been a city-boy living in Pretoria I still have those farming roots, Northern Ireland seems to have a good balance of both."