It depends. While most of the competitive gaming leagues I checked out don't mention anything about drug testing explicitly, the International eSports Federation (IeSF) has partnered with the World Anti-doping Agency (WADA), prohibiting a whole standardized myriad of performance-enhancing drugs, testing winners and random other players for them. There is a process through the World Anti-doping Agency for exemptions, which essentially requires the WADA to explicitly approve of someone using a drug in competition because they have a medical condition.
There is a very strict process for therapeutic exemptions, however. A TUE is granted if and only if an athlete absolutely needs to take the prohibited substance for medical reasons, the prohibited substance doesn't provide any additional enhancement of performance other than what would be expected by an athlete returning to normal health, there is no alternative, and the necessity of use isn't a consequence of dependence. Adderall, typically associated with performance enhancement for video games, does not meet any of these criteria.
Other leagues have rules governing showing up to events intoxicated or clearly under the influence of drugs, if not explicitly, in the "tournament officials reserve the right to disqualify any player at any time for any reason" clause.
1. How do teams qualify to play in the Challenger Series?
Well this is a little bit difficult for me to explain but, here you have the official page.
2. How do teams qualify to play in the LCS?
At the end of the season, the top seven teams will automatically
re-qualify for the LCS. The 8th and 9th place LCS teams will then play
in a Promotion Tournament against the 2nd and 3rd place Challenger
Series (CS) teams to retain their spot in the LCS. The 8th place LCS
team will get their choice of CS opponent. The 10th place LCS team
will automatically be relegated to the Challenger Series, while the
1st place Challenger team will automatically qualify for the LCS. You
can find more information on the 2015 LCS changes here.
EDIT: Rules have changed since now:
For NALCS:
LCS Teams 1 through 8 auto-requalify team 9 and 10 go into a relegation, double elemination tournament against Challenger 1-2.
Seeding for first round is NALCS 9 vs Chall. 2 and NALCS 10 vs Chall. 1
For EU LCS
Teams 1 through 4 of each group auto requalify, team 5 goes to relegation.
Both finalists of the Challenger series go to the double elimination relegation tournament.
The Relegated team from the EULCS with the best record decides who, from the 2 teams from challenger they want in 1st round. The relegated team with the worst record gets the other challenger finalist.
3. Are there major differences between EUW and NA?
The rules and the way to qualify for each region are the same.
4. Are there restrictions to the members nationalities?
I think that the unique restriction is about the gaming brand, they change it last year, because of Samsung White and Samsung Blue. And now its company or brand can only have one team in the LCS or challenger series.
Best Answer
It's all about being able to easily identify characters, especially in large team fights. While most competitive players are probably able to identify characters no matter what skin they're using, it helps take away some distraction from the core game.