Historical Rules · 13 November 2015
Rule 121.1c
Official source text from the 13 November 2015 Rules release
If a player has ten or more poison counters, he or she loses the game as a state-based action. See rule 704. A player is “poisoned” if he or she has one or more poison counters. (See rule 810 for additional rules for Two-Headed Giant games.)