It's not too common in most countries.
Euthanasia is limited to only a few states of the U.S.A. along with D.C. However, there are many stipulations and other things that are to be adhered to and to make it in any way legal. (Check each state to learn if they have any permissibility for this. If not, prison could be in the future for anyone assisting.
With regard to other countries, Belgium is on board, The Netherlands as well. Again, there are rules and regulations for deciding who is eligible.
It's probably helpful to retain an attorney if one is considering this.