I know few guys that have been using ghrp/ghrh peptides for a few years already. They look and feel healthier then ever. I think it's ok to use them long term, because all they do is signal your body to release HGH, there's nothing bad about it. So far I have been using melanotan for a year, and will probably continue to use it forever!
There's many people using long term, probably more than people think as there still seems to be a stigma attached to using them in the first place, never mind over a long period of time.
Even people that use MT can be looked at funnily if they tell people they are injecting theirselves to improve their skin tone and tan, so a lot of people choose to not say anything at all.
I've been on it for a few years now. I remembered experiencing palpitations during my first use, though it wasn't that serious so I didn't take it as a big deal. Eventually, it went away. So far, I don't have any problems with it.