One must try and obtain kosher medicine, but if none is available, then one must take the medicine that is available, even if it is not kosher. Cults are said to have an immutable dogma. Most religions have that. Judaism has it too. Judaism, however, is much more flexible than almost any other religious dogma.
Most cults offer a newly invented doctrine, often a composite of other popular religions.
Judaism teaches a way of life that has been a tradition for over three thousand years. If you are Jewish, then the overwhelming likelihood is that your great-grandparents were fully observant Jews, and their parents were, and their parents were, and so on back for many generations. Surely you cannot believe that your own grandparents were members of a cult.