JOHANNESBURG — The World Anti-Doping Agency has approved doubling bans from two years to four, ensuring serious drug cheats will miss at least one Olympics.

The tougher bans were part of a revised international anti-doping code agreed on and adopted by WADA on Friday at the end of its four-day summit in South Africa. The code will come into effect on Jan. 1, 2015, and in time for the Rio Olympics.

WADA also has strengthened its powers to punish coaches and trainers who help athletes dope, and has placed more emphasis on launching its own investigations to catch cheaters.

Another key change is WADA's ability to tell sports which illegal substances they should be testing for.