Is there a guideline for how often is reasonable? I haven't found a clear answer — most sources either say nothing or say 'use sparingly' which isn't helpful.
There's no formal clinical guideline because this hasn't been studied in controlled settings. What we can reason from the pharmacology:
Tachyphylaxis (short-term tolerance to sodium channel effects) can develop within a few days of daily use. The receptors adapt. Based on the mechanism and what people report consistently, a minimum of 48 hours between sessions seems to preserve effect reasonably well. 72 hours or more is safer if you want consistent experience over time. Some people use once per week and report no tolerance issues at all.
Daily use for anything beyond a short test period isn't something I'd recommend. It's not that the compound accumulates — it clears relatively quickly — but the receptor-level adaptation is real and faster than most people expect.
From experience: I tried daily use for two weeks to see what happened. By day 5–6 the effect was noticeably reduced. By day 10 it was minimal. Three days off reset it almost completely.
I settled on 2x per week maximum with at least 3 days between sessions, and that's been stable for about 8 months now. The effect hasn't noticeably degraded. The weeks I've pushed to 3x I've noticed it weaker by the third use. Just data points, but they've been consistent.
The tolerance question also intersects with the 'why are you using it' question. If you're using it to chase an effect that requires more and more frequency, you've built tolerance and are chasing something you won't catch. That's a pattern worth stepping back from. Take a full week off, reset, and ask honestly whether the baseline use is still doing what you wanted.