Started flu 4:30am Wednesday. Took 2 charcoal pills Wednesday evening. Started taking Flu Alka Salzer, last does being Friday afternoon. Felt much better Friday morning however started having very small amounts of black stool. Took pepto bismal 3 times Friday night, last dose being 1am (Saturday). Progressed to full black liquid Friday night. Was up every 2-3 hours throughout last night and continuing. Haven't eaten and only drank water since 5pm Friday. Is the black just after math of the charcoal and pepto or should I worry about something else? How long should I let it continue before considering going to doctor?

A black stool may be caused by bleeding somewhere in the upper or lower gastrointestinal tract. Blood is an important warning sign for hemorrhoids as well. This is a clinical explanation for your problem but may or may not be the cause. I am thinking the charcoal pills may have done it, however, you should really see a doctor.

Tick

I suggest not taking any NSAIDS such as Ibeuprofen.. also no Pepto Bismal for the diarrhea. It can cause black stool and is usually from bleeding.