A method for treating anxiety disorders, affective disorders, intracranial injury, spinal cord injury, neurodegenerative diseases, sclerosis, migraine, fibromyalgia and cerebrovascular disease, using melatonin derivatives is disclosed. A specific melatonin derivative for use in the disclosed process is 13-methyl-6-chloromelatonin (otherwise referred to as (R)-N-[2-(6-chloro-5-methoxy-1H-indol-3-yl)propyl]acetamide).