Is it safe to take m amphet salts if you have low blood pressure?

For ADD, yes: I'm assuming this is an add medication question. If so, then the answer is a categorical yes, barring any other contraindications for the meds. If you're talking about recreational amphetamines or abuse of add meds, then no - significant damage can occur, though it'll have nothing to do with low blood pressure.

? : If m amphet mean "methamphetamine", the answer is no: it is never safe to take methamphetamine.