Melatonin rhymes with:
serotonin, seratonin, serotonin, bonin, cronin, ronin, seratonin, serotonin, antonin, behunin, benin, bonin, bonnin, bradykinin, branin, canin, chanin, chernin, clanin, clendenin, cronin, dennin, dobrynin, dornan, dornin, dubinin, durnin, fannin, henin, jenin, junine, kunin, lignin, magnin, monnin, pankonin, ronin, runnin', seratonin, serotonin, simonin, tinnin, wolanin
Melatonin sounds like:
malathion, malden, malleton, maulden, mauldin, mealtime, meldon, meltdown, melton, militiamen, milton, molden, molten, molton, moulden, moulton, muldoon, muldowney, multnomah