It’s literally used by dentists and is more commonly known as laughing gas.

It’s considered a low risk anesthesia. The only talk on erowid is that it can cause temporary hypoxia by displacing oxygen in the lungs which might lead to some minor death of brain cells just the same as inhaling helium to make your voice sound funny.

There is some reports of very long exposure having some effects on neurons, but that was inconclusive and more around anesthesiologists working in poorly ventilated rooms being exposed daily.

As long as you aren’t putting yourself in a place where if you inhale too much and pass out that you are still breathing n2o you should be fine. And so long as you aren’t inhaling directly out of a freshly cracked can where it comes out at literally freezing temperatures.

Most people will use a cracker that fills a balloon and is mostly safe. Just do so in a well ventilated location.

www.erowid.org/chemicals/nitrous/nitrous.shtml