No there shouldn't be any big side effects. Melatonin is a hormone naturally produced by the human body. Its function is to be like a switch that tells the body when to go to bed.
Habitually we start with a dose of 5mg and can increase every week if needed up to a maximum of 10mg per day. It is usually taken 30-60 minutes before bedtime! There are no long term side effects either but if you have insomnia the best solution is to address the source of the problem (ex: stress, anxiety, no sleep routine)
Happy evening!
Calin B (pharmacy student supervised by Alexandre)