Does poison damage dealt to a commander count toward poison counters in Commander?

First, a clarification: Magic doesn't have a mechanic called 'poison damage.' Poison counters are given to players by creatures with infect (CR 702.90) or toxic (CR 702.164), or by specific card effects. Infect creatures deal damage to players in the form of poison counters instead of regular damage — meaning a 3-power infect creature gives an opponent 3 poison counters rather than 3 life loss.

In Commander, the poison counter rule from the Comprehensive Rules (CR 104.3d) still applies: a player who has 10 or more poison counters loses the game. The Commander format rules do not modify or remove this win condition — it functions exactly as it does in other formats.

Your commander itself is not relevant here. Poison counters are tracked on players, not on commanders. If your commander has infect and deals combat damage to an opponent, that opponent receives poison counters equal to your commander's power. Those counters accumulate normally toward the 10-counter threshold.

Concrete example: You control Skithiryx, the Blight Dragon (a 4/4 with infect) as your commander. It deals combat damage to an opponent — that opponent gets 4 poison counters. Over two more attacks, they accumulate 10 total and lose the game immediately per CR 104.3d, regardless of their life total.

Note: Commander damage (21 combat damage from a single commander) is a separate rule (CR 903.10a) and does not interact with poison counters — they are tracked independently.