Q. Someone that can’t fast even on the night of Tisha Beav, should he say havdala immediately, or wait until he has to take his medicine with some food?
Thank you so much.

A. Shaarei Teshuva (556: 1) quoting Knesses Hagedola maintains that he should say havdala at the end of Shabbos. Horav Shlomo Miller’s Shlit’a opinion is that he should wait until the time he has to eat or drink, even if it is a short time. The Rov added that the ill may meantime get well and be able to fast.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.