I took l-theanine for a long time, four or five years, and with tolerance I don't know whether or not it still had any positive effect but that same concern for tolerance also made me too cautious to stop it and take the possible rebound.

That happened anyway for silly reasons and it took me a few days to realize that the serious and ever increasing neck pain I had been suffering for a couple years (and blamed on computer use) had simply vanished. It's been a couple of months and what had been chronic has not returned with even a trace.

There was no psychological expectation or placebo factors because I never had considered the possibility that they might be connected, the cessation was inadvertent with no intent and something I thought little about, and it was several days before I realized that I had been completely free of increasingly disabling pain for the same several days. This could be coincidence but I don't think so. Just sayin'.