Crystal meth is highly addictive. The more you do it the more likely you are to become dependent on it.
The effects of meth can sometimes vary depending on the person's economic background. A wealthy user has access to the best medical care so we don't always see tell-tale signs of excessive use. In some of those cases there are no jobs to lose and with a continuous cash flow no need to steal from or alienate family and friends.
Let's not delude ourselves about Agassi's admission. If he did meth more than once in '97 there's a 99% chance that he's done it more than once since. If in that very slim chance Agassi stayed clear of the drug since '97, talking about the euphoric feeling and the high he got while doing meth more than likely reawakened old cravings. Along with being very addictive there's also a very big chance for a meth relapse no matter how long you've gone without it.
I'm not buying Agassi's book. Agassi is looking to be rewarded for bad behaviour here. He accepted millions to write a controversial book about something he supposedly regrets. He's going along with this very calculated marketing plan to release snippets of the book ahead of its release to generate interests so he'll make even more once the book skyrockets up the bestseller list with the help of gullible fans.
If Agassi is truly sorry he wouldn't be looking to profit from it. If he's truly remorseful he would take all that money he's getting from this book and donate it to drug treatment programs, anti-doping programs, and families who have been destroyed by drug addiction. Agassi wants us to believe that he's unburdening his soul but in reality all he's done is sold it.