Nothing severe that I know of, however I know that it was intended for a short-term solution. I am not sure there is a ton of research yet on the long-term effects. I guess overall I would just hope that after changing, diet and lifestyle most people are able to fall into a natural sleep rhythm and no longer need to continue Melatonin. I am not a sleep expert by any means, I just don’t like taking supplements long term. However I do think that lack of sleep long term is potentially far more harmful than Melatonin. I would address it with your Dr. though if you are concerned.
Here is an article on the Mayo Clinic site regarding Melatonin:
