Mr Gosling, from Leicestershire, joined the trial in July after being referred to Prof Matt Brown, who is leading the UK’s branch of the trial.
He was told his AAA, a balloon-like swelling in the abdominal portion of the body’s main artery, was 1.57in (4cm) wide.
“I asked what I could do to stop it growing and that’s when they told me about the trial,” Mr Gosling said.
“It also means my condition is very closely monitored, which can only be a good thing. Hopefully it will help a lot of people like me in the future.”
The university said an AAA rarely caused symptoms unless it ruptured, but Mr Gosling has stopped doing certain things like lifting heavy objects while helping his son on the family farm.
During the first stage of the trial, he was given metformin in gradually larger doses over six weeks to check that he had no problems with the drug.
He then moved to the next phase, where he is taking either metformin or a placebo, and having regular check-ups on the growth of his AAA.