nitrous inhibits b12 production, so if you use a shitton in one sitting then take a few weeks break youll be fine just supplement b12

but if u use a little bit periodically over a couple days that could start to degrade your nerves permanently due to lack of b12.

but you cant produce less than zero and any nitrous puts you at zero so if youre gonna use it do big one night binges then take a month off and supplement b12 for a bit. in this case its theoretically pretty harmless.