Reading over the rules for poisons on page 172 I noticed that it gives the difficulties for resisting various poisons and the results of threat generated on the resilience roll, but it also mentions how the GM could spend despair.
This strikes me as odd since the difficulty dice don't generate despair.
Without the challenge die present in the roll, how would the despair function of poisons ever come in to play? Well, other than a GM holding on to previously rolled despair for use later in the session.