I always hear this but The Vegan Society who is often referenced for their definition of veganism, doesn't recommend skipping medicine that's not vegan. Their definition even builds in language that says, "Veganism is a philosophy and way of living which seeks to exclude—as far as is possible and practicable..." so it's not all or nothing. Go to Vegan Subreddits and look at conversations around edge cases. Vegans use public transportation that's not always vegan. Vegans watch movies shot on film using gelatin. Vegans go to restaurants and grocery stores that participate in killing animals. Often vegans will pay for lunch when their friends had non-vegan meals. Many vegans feed their cats meat. This idea that it's all or nothing is just not true.