Andre Agassi believes drug testing in tennis is now water-tight and does not think he would have fooled the authorities today.

The American shocked the tennis world with the revelations in his new autobiography 'Open' that he failed a test for crystal meth in 1997 and then lied to escape a suspension.

Governing body the ATP have come in for criticism for allowing Agassi to talk his way out of the situation, but he said: "(In 1997) we were at the infancy of drug testing.

"This was pre-era of sensationalising drugs in sport and, as a result of tennis pushing itself forward to protect its integrity, we reached out to the World Anti-Doping Association two years later and they've been a fabulous partner who've done a tremendous job in protecting that integrity of keeping drug cheaters out of the sport.

"They've tested me specifically 150 times. Our sport should be proud of how we've moved forward through this day and age. I don't think it's so easy, not when you're getting tested 15 or 20 times a year.

"It's a very sophisticated approach now. It's thorough, it's random, urine and blood, and any initial positive test is run though a process."

Agassi, who won eight grand slam titles and was the last man before Roger Federer to triumph at all four events, kept his drug-taking a secret and does not know whether other players also escaped censure.

"It's hard to speculate," he continued. "I saw what I could hide as it relates to my usage. People around me didn't know I was doing it. My wife at the time (Brooke Shields) didn't know.

"They saw the results of how I felt. I did appear depressed, disconnected, disengaging with my tennis and with some relationships. You can only hide it for so long.

"I turned it around before I actually confided in anybody."

Having dropped out of the world's top 100 in 1997, Agassi returned to the top of the game and became one of its most respected figures before retiring in 2006 at the age of 36.

With many of his rivals calling it a day around their 30th birthdays, the former world number one revealed he kept going in part because of a sense of "duty".

"I had a duty to tennis. I owed a lot to tennis," he said.

Agassi also made headlines with the claim he "always hated" tennis, and he believes youngsters should think hard before deciding to pursue a career in the sport.

"The truth is, you don't succeed in this sport unless you give everything to it every day starting from a very young age," he added.

"Pushing yourself and giving your all to something is a healthy thing ultimately but I do think it's a very hard life, a lot harder than people realise and I think it comes with more of a cost than people realise.

"As a result, there's other ways to discover yourself. Nothing in life is easy but tennis is exceptionally hard."