Insomnia Support Group
Insomnia is a symptom, rather than a disease, and is characterized by inadequate quantity or quality of sleep. People with insomnia complain of difficulty falling or staying asleep, which results in significant impairment of daytime functioning. Insomnia is categorized as transient (shorter than one week), short-term (one to three weeks) or chronic (longer than three...
But if you start taking more and more and more....well even Vit C is toxic when someone takes a thousand times what you'd get from eating oranges.
If you're concerned...it would be a good question for your doctor.
I do not believe that there have ever been long-term studies on the effects of using melatonin. Who is going to pay for what would be an expensive study of an OTC medicine? The "Catch 22" of any OTC medicine.
Check out CBT sleep training programs, they are the substance free gold standard. CBT enables you to address the true underlying root issues that disrupt sleep in the first place. Of course this presumes you have no untreated medical issues causing the insomnia.