Seen a lot of posts recently about long term users stating that Melanotan is becoming less effective for them. Perhaps there is a large scale supplier issue, but it appears that the MC1R receptor can become de-sensitized to Alpha MSH/Melanotan. MC1R is the main receptor that Melanotan binds to that causes tanning and according to a Clinuvel patent this receptor can become de-sensitized. So taking a break should make everything go back to normal, similar to any drug tolerance such as alcohol.
"administering to the subject an alpha-MSH analogue in an effective amount and time to induce melanogenesis by the melanocytes in epidermal tissue of the subject without inducing homologous desensitization of the melanocortin-1 receptors of the subject"