diarrhea; loose stomach; This is a spontaneous report from a contactable consumer (patient). A 82-year-old female patient received BNT162B2 (PFIZER-BIONTECH COVID-19 mRNA VACCINE; Formulation: Solution for injection, Lot number: FA6780, Expiration Date: not reported) via an unspecified route of administration in left upper arm on 30Jul2021 as dose 1, single for COVID-19 immunization (at the age of 82-year-old). Medical history included she saw her doctor for her chemo maintenance. She was in remission for Leukemia, ongoing antiviral treatment , pancreatic failure from an unknown date and unknown if ongoing, ongoing thyroid hormones decreased. Concomitant medication(s) included acyclovir [aciclovir] (ACYCLOVIR) taken for antiviral treatment from Jan2020 and ongoing; furosemide taken for water pill from Jan2020 and ongoing; levothyroxine taken for thyroid hormones decreased from an unspecified start date and ongoing and been on it since age 65; pancreatin (CREON) taken for pancreatic failure, been taking it for 11 years. The patient previously took amlodipine [amlodipine besilate] and experienced joint swelling, lisinopril and experienced joint swelling, methotrexate and experienced inflamed lungs, dexamethasone. The patient experienced diarrhea and loose stomach on 31Jul2021. It was reported that, In Aug2019 she was put on Amlodipine and Lisinopril, but she couldn't take them. She got off of both of them within a month. They caused her ankles to swell up. It went away after she got off of them. Levothyroxine, it was crazy because she was thin. She didn't want to took it because she didn't want to loose weight. She lost 5 pounds when she got on it. It was in pharmacy vial. Use before date was 29May2022. Didn't have lot or NDC to provide because it was in pharmacy vial. She took Creon for pancreatic insufficiency. She had hers late because she had to stop Methotrexate to get the vaccine. She took Dexamethasone for five days after chemo. She had to wait to stop both of those drugs before got the vaccine. She had the bottle and she wrote on there do not take. The bottle said oval, yellow tablet. Caller clarified product was in a pharmacy bottle strength: 2.5mg; Use before date: 01May2022. She was supposed to take 12 tablets one day a week. She took it on Wednesday. She would take six at lunch and six at dinner. Methotrexate caused inflamed lungs and she ended up in the hospital. She went in the hospital on 28May2021 and was there for 9 days. She stopped taking Methotrexate when in the hospital. She was supposed to take it the day of chemotherapy, but that day she did not take it. She got diarrhea and loose stomach because she didn't make enough enzymes. Right now she couldn't eat what she wanted and it was prescribed by a gastroenterologist. She had appointment in Oct. The first one was Pfizer and on 30Jul2021. When she had it, it was fine but the next day after the first one she had diarrhea and loose stomach. In an Investigation everything was ok with that. No further details provided. She was worried about getting booster. She was not sure if she was going to get the booster. She hoped they didn't give her something that was old. The patient underwent lab tests and procedures which included blood test: she had blood test which were fine on an unspecified date. The outcome of the events was unknown  Follow-up attempts are completed. No further information is expected.