[graderjs]

For example, I can chew nicotine gum during exams but I can’t do yoga.

But if you're doing yoga the benefits extend in time far beyond the session. So say you're doing hatha yoga 3 times a week. You're going to be relaxed and calm; your nervous system is going to be more resilient to stress; You're going to be more focused; you're going to sleep better and need less sleep -- for that whole week. So the "half-life" is a lot longer compared to nicotine.

Nicotine is only toxic in high doses

But also...acutely toxic at high doses. It's still a toxin at low doses. And I wouldn't say how it's giving you the relaxation it is healthy for you at low doses. But yoga is.