England saw a decrease in suicide rates in the '60s & '70s last century when the levels of carbon monoxide in the natural gas supply were reduced. As a result of this change, people stopped being able to easily commit suicide by sticking their head in the unlit oven and turning it on.

It’s not like these people were institutionalized and physically prevented from harming themselves. Making means of suicide too really available seems to allow people to kill themselves who otherwise would not attempt it.

Reducing access to guns- besides the obvious decrease in homicides - will likely cause a noteworthy reduction in suicide, too.