[hilbert42]

Insensitivity to caffeine is pretty common. As I said in my post, I'm insensitive to it but then I've regularly consumed large quantities of it almost every day since I was a kid (I've always drunk very strong tea and coffee without milk or sugar), so I'd expect to be desensitized.

Perhaps there is an ADHD connection but that desensitization also occurs to those who don't have it. Caffeine is just like any other psychotropic drug, it doesn't take long to develop a tolerance.

BTW, 30mg caffeine is hardly enough to get one off the starting block, a strong cup of coffee can have three to five times that amount.