There was a period of several months where I was inhaling 50+ chargers of nitrous oxide on a daily basis, sometimes 100 or more. Even though I dearly loved the stuff (and could actually afford it at the time), I finally managed to stop when the tingling sensation in my fingers and toes got too strong to ignore, even in my heavily anaesthetized state.
Of course I can't be sure, but the symptoms were more than a little bit worrisome. I was at least aware at the time of the possibility that nitrous (ab)use might cause a vitamin B12 deficiency, which could in turn cause peripheral neuropathy.
If you are using nitrous day-in day-out, taking B12 vitamins is useless, since the presence of nitrous oxide in the body prevents B12 from being absorbed (IIRC, at least). The obvious solution is to take breaks and allow the B12 to replenish itself.... but I found this to be much easier in theory than in practice.
It is embarrassing to admit this, but I've never had such intense psychological cravings for a drug before or since: I found myself sucking from the dispenser in some pretty inappropriate places (on the job, behind the wheel), with both palms rubbed visibly raw from the effort of screwing in hundreds of chargers a week; lying immobilized on the fold-out couch after a heavy session, watching in a state of total indifference as vivid images showed me all the ways my life was crumbling; rushing out to seedy porno shops on an almost-weekly basis, paying an outrageous price to obtain 20 measly chargers in a box covered with humiliating "erotic" photo art, all to avoid taking a day or two off from the nitrous (God forbid)....