ויאגרה – כשרות, ובשבת

1. I have never heard of any kashrut problems with Viagra.

2. According to R. Yehoshua Y. Neuwirth (author of Shemirat Shabbat ke-Hilkhata) and R. Shlomo Deichovsky (dayyan in the Supreme Rabbinical Court) there is no halakhic prohibition against medical treatment that enables an impotent patient to function on Shabbat.

Sources: For R. Neuwirth’s opinion see Nishmat Avraham vol. 5 (Heb.), p. 21. For R. Deichovsky’s teshuva see The Proceedings of the First International Colloquium on Medicine, Ethics and Jewish Law (The Schlesinger Institute, 1996), pp. 187-8 (pp. 144-5 in Hebrew edition).