Diarrhea; This is a spontaneous report from a contactable consumer (reported for herself). A 79-year-old female patient received bnt162b2 (BNT162B2; PFIZER-BIONTECH COVID-19 mRNA VACCINE; Solution for injection, Batch/Lot number was not reported), dose 1 via an unspecified route of administration on 04Feb2021 (at the age of 79-years-old) as dose 1, single for covid-19 immunisation. Medical history included ongoing irritable bowel syndrome (she has had it for years, probably about 30 years ago and it doesn't go away) and ongoing arthritis (she has arthritis so before she goes to bed every night, she takes 2 Advil). Concomitant medication included Advil (2 Advil every night) for arthritis. The reporter stated that, she got first dose on last Thursday, it was her first shot, she was supposed to get the next one in 3 weeks. She was reading on the internet before the day of vaccination at night that if they take Advil, it would reduce the effect of taking the vaccine. The reporter didn't get any information like that when they got the vaccine. She had arthritis so before she goes to bed every night, she takes 2 Advil, does that effect the vaccine and if so what percentage of the efficacy was affected. The reporter said she had another question. Her and her husband both didn't know they shouldn't take headache medicines and her husband gets migraines and the day before the vaccine he took an excedrin and she took advil every night so they both were wondering and also the day after the vaccine, they did not feel bad the first day but the next day they had diarrhea. Caller said she had Irritable bowel syndrome so she sometimes had diarrhea, but her husband never had diarrhea and they both had diarrhea the day after. The reporter stated that the diarrhea was gone now for both of them but in the information the hospital gave with the possible side effects, that wasn't mentioned at all there was a bunch of different things but not diarrhea. The reporter stated that she had IBS but her husband didn't have that was why they thought it may have been the vaccine. She had that problem all the time with IBS so never know if it was with the IBS or not. The outcome of the event was resolved.  Description of Product Complaint: Description of complaint: Caller is calling about the Pfizer COVID 19 vaccine she got last Thursday, it was her first shot, she is supposed to get the next one in 3 weeks. She was reading on the internet last night that if they take Advil, it would reduce the effect of taking the vaccine. They didn't get any information like that when they got the vaccine. She has arthritis so before she goes to bed every night, she takes 2 Advil, does that effect the vaccine and if so what percentage of the efficacy is effected. She says she has another question. Her and her husband both didn't know they shouldn't take headache medicines and her husband gets migraines and the day before the vaccine he took an Excedrin and she takes Advil every night so they both were wondering about that. Caller does not have their vaccine record cards with her at the time of the call. She is not able to provide NDC lot expiration for either of their vaccinations. She confirms her and her husband both received the Pfizer COVID 19 vaccine. Product strength and count size dispensed:  Additional lot numbers:  Is a sample of the product available to be returned, if requested (Y/N):  Packaging sealed and intact?   Information about lot/batch number has been requested.  Follow-up attempts completed. No further information expected.