Taking Medicine on Shabbat-Part I by Rabbi Chaim Jachter

 https://www.koltorah.org/halachah/taking-medicine-on-shabbat-part-i-by-rabbi-chaim-jachter

People commonly ask why this rabbinical prohibition still applies if its reason is no longer relevant. The answer is that rabbinical prohibitions remain even if their reasons no longer apply. The Gemara (Beitzah 5a) articulates the rule that כל דבר שבמנין צריך מנין אחר להתירו, “once the rabbis issue a decree only a rabbinical assemblage of equivalent stature can overturn it.” The Gemara cites a biblical precedent for this rule. Today there is no rabbinical assemblage of equivalent stature to the rabbis of the Gemara. Hence, Chazal’s decrees still apply even if their reasons are no longer relevant.

Rav Yosef Dov Soloveitchik (Nefesh Harav p.173) specifically invoked this principle when he ruled that even today we are prohibited from taking medicine on Shabbat. Rav Eliezer Waldenberg (Teshuvot Tzitz Eliezer 8:15:15:4) adds that the reason for this decree is still relevant, as even today many people grind medicines when preparing home remedies.