You could buy it at a close small err...place
It would be close to the pharmacy section.
Physically addictive? No not really, because it just gets your natural melatonin going. Try to take the melatonin pills on a regular basis, and since it is a natural hormone, (not anyway related to puberty hormones) your body recognises that. It will notice the time of day, from when you woke up to when it's usually time to go to bed, and how much your body is worn out. So the body will produce its own I belive. It won't work nearly as good if you have a random scedual. Organise things, and you'll have a good, healthy sleep at night