[fso301]

If you can do meth, and still manage to play professional tennis at that level, it’s more of a testament to his talent than anything.

I'm not a medical professional but my understanding is drugs affect people differently. The Japanese who invented it also distributed it amongst military forces in WWII to help them make that extra sacrifice for the emperor. In WWII, meth under the name pervitin was used heavily by German forces.

[BenKenobi]

It also explains why he was so up and down, and then refocused later on in his career. In 1997, he collapsed and had to start all over again from scratch.