True. Sometimes the "can't sleep" part is not due entirely to the effects of amphetamines, but is due to residual effects on the brain, such as racing thoughts that prevent you from sleeping. That's why I said you can't expect them to work very well, or at all, if you're still under strong influence of speed. Works best if the meth and/or speed in your system has already decreased. Those drugs just provide a "nudge" in the right direction.
Nothing blocks the affects of speed/meth AFTER you've taken it, but there is(are) drugs that seem to minimize the effects if taken BEFORE speed, but that's just a waste of money from both directions, playing both sides against the middle.