That is why we produced 0.5mg tablets. You will note that when a medicine is in tablet form 1 or 2 tablets is almost always the appropriate dose. It's a widely taught formation technique relying on psychology.
I took 100mg just to test it's inherent safety. I was somewhat sleepy but was still able to function. It IS a2/a3 selective, but only by a factor of about 6 so while affinity is lower, if you take enough it will also bind to a1 & a5 although we really did not intend people to take more than 1mg every 6 hours.
<EDIT> it's Ki values are a1 = 5.3, a2 =1.4, a3 = 1.7 & a5 =4.9. Remember that Ki values are on a logarithmic scale so in fact, if you do the maths, it's a lot more than x6. More like x36 I was being lazy. Sorry about that.</EDIT>