Speaking at his launch event in central London on Wednesday morning, the frontrunner to succeed Theresa May was asked directly if he had ever used the drug.
In response the former foreign secretary said voters wanted the leadership candidates to focus on “what we can do for them”.
It comes after Michael Gove’s rival leadership bid was knocked off course after he confessed to having used the drug.
During a Q&A with journalists today, Johnson was asked whether he was telling the truth in the below 2007 interview with GQ.
Piers Morgan: What did you think of Cameron standing his ground over the drugs issue and refusing to say whether he had ever taken them?
Boris Johnson: I thought he was right. I’m not a great drug man myself.
PM: You once alluded to the fact that you tried cocaine but sneezed on it.
BJ: Yes. I tried it at university and I remember it vividly. And it achieved no pharmacological, psychotropical or any other effect on me whatsoever.
PM: Some of it did creep in to your big hooter, then, despite the sneeze?
BJ: It must have done, yes, but it didn’t do much for me, I can tell you.
Johnson would only say today: “I think the canonical account of this event when I was 19 has appeared many, many times.
“I think what most people in this country really want us to focus on in this campaign is, if I may so, is what we can do for them and what our plans are for this great country of ours.”
Asked earlier in the press conference whether he had ever done anything illegal, Johnson said: “I cannot swear that I have always observed a top speed limit of 70mph.”
In a 2008 interview with Marie Claire magazine, Johnson was also asked if he had ever taken cocaine.
He said: “Well, that was when I was 19. It all goes to show that sometimes it’s better not to say anything. I thoroughly disagree with drugs. I don’t want my kids having drugs.”
In a 2005 appearance on Have I Got News For You Johnson also said: “I think I was once given cocaine, but I sneezed and so it did not go up my nose. In fact, I may have been doing icing sugar.”