You probably shouldn't be using the word "responsible" then, because it has a particular meaning that implies, whether you mean to or not, that using them any other way is irresponsible. I'd say every 2 weeks to keep tolerance low. Used more frequently, and you will develop lasting tolerance. It does partly depend on the dose, though. If you take low doses, you could conceivably use it more often without much increase in tolerance.

The risk of long-term cognitive, emotional, and neuro-chemical/structural changes is generally only an issue if you are using daily or near daily, at least based on what we know of Ketamine. The other dissociatives could be different, but scientific research hasn't been done yet. In the case of MDMA, the long-term effects of chronic long-term usage have been established, but we don't have that yet for most of the arylcyclohexylamines, and we may never due to their relative unpopularity.