Look at what happened when England reduced CO access by switching from coal gas to natural gas.

Over time, as the carbon monoxide in gas decreased, suicides also decreased (Kreitman 1976). Suicides by carbon monoxide decreased dramatically, while suicides by other methods increased a small amount, resulting in a net decrease in overall suicides, particularly among females.

https://www.hsph.harvard.edu/means-matter/means-matter/saves-lives/

Suicide is often a matter of convenience. If it’s harder to kill yourself, many people are less likely to do it. I suspect reducing access to guns would reduce suicides just like it did with coal gas.