There are three Alchemy keywords exist in vanilla game:
MagicAlchDamageHealth [KYWD:0010F9DD]
MagicAlchDamageMagicka [KYWD:0010F9DE]
MagicAlchDamageStamina [KYWD:0010F9DC]
it seems like that these KWDs should be given to the corresponding alchemy poison damage effect, like:
AlchDamageHealth, AlchDamageMagicka, AlchDamageStamina, AlchDamageHealthDuration, AlchDamageMagickaDuration, AlchDamageStaminaDuration,
respectively.