You can build tolerance or resistance to almost anything, and meds or herbs which act as central nervous system depressants tend to have that problem for almost everyone. The best way yo avoid it is to take (herbs OR Rx meds) stuff for sleep or to help you relax as infrequently as possible. At the least, skip a night (or day) once or twice a week. And if you find yourself taking more for the same effect... talk to your doctor or reevaluate your regimen...Valerin root gives a calming effect. I use to use it for a sleep aid, but I thought that I built up a resistence to it.
Judy