Right...
I actually read through some medical journal articles when looking for relief from my full-body itching, and it's been found that it takes 75 times more histamine to produce an itch than Benadryl. That's pretty amazing. Plus... it's cheaper for me to buy than Benadryl, so it's really the only antihistamine I use.
Plus, although I haven't noticed it myself, it's considered to be an anxiolytic, which I can only see as being helpful while sitting in a chair having needles dragged across your chest for hours.
Still... if you feel the need to scratch, give it a little slap instead.