> I don't know the health effects of pure nicotine (say, in liquid form) vs caffeine, but one is certainly much more addictive than the other.

Which one did you have in mind, and why do you say certainly?

Nicotine is more addictive than caffeine. I'm not going to find peer-reviewed, double-blind studies to back up my claim. I'm going to go with the anecdotes I've heard for decades and from personal experience.

I'm not going to argue with your opinion -- but I suspect you are conflating tobacco (usually smoked) with nicotine.

Isn't nicotine the primary addictive chemical in cigarettes and vapes

There are "whole tobacco alkaloid" liquids (full-spectrum extract of tobacco vs. pure nicotine) available which contains a lot of the other stuff. Probably more addictive so I'd avoid it if your goal is to quit.

I believe it. There's vapes for everything. Was just focusing on parent's nicotine addictiveness statement that gwern addresses.