According to the query of iQiyi, the plot of Ning Yuanzhou poisoning in the TV series "The Difference of One Mind Going Down the Mountain" occurred in 19 to 20 episodes.
In episode 19-20 of "Crossing Mountains and Rivers with One Heart", a poison called "Ten-day Drive Machine" was given by the Prime Minister of Wu before Ningyuan Ship set out to contain Ningyuan Ship. Ning Yuanzhou needs to take an antidote every ten days to alleviate the toxicity. Once delayed on the road, Ning Yuanzhou can't reach the designated place to get the antidote.