there was a csi los vegas episode with this very theme. a gambler called the candy man, because he ate nothing but M&Ms constantly at the table, was stiffing a waitress and she did the standard tetrahydrozeline(eyedrops) in the drink to give him the runs and make him miss play as retaliation(heads up, tippers). instead he keeled over dead. the combination of the lead and the thz gave him a cardiac arrest. they concluded she didnt kill him on purpose - he did it to himself. well, sort of, she still assaulted him but that wasnt mentioned.