Melatonin is a hormone mainly produced by epiphysis, or pineal gland, which is at the base of our brain. In the blood, melatonin levels increase with caloric restriction and darkness while drop down with daylight and aging. Melatonin is produced from serotonin, whose values are higher during the day and drop down by night. This melatonin-serotonin alternation determines vital rhythms, if this alternation functions well it provides a restful sleep, in fact, melatonin has a relaxing effect, energy during the daytime, the neutralization of free radicals that have accumulated during the day, protection against aging, improvement of the immune defenses. Often, in cases of insomnia, especially when the person has problems to fall asleep but then he or she is able to sleep continuously until the next morning with a difficult awakening, or when the sleeping schedule is altered as in the case of people who work night shifts or are traveling in places with another time zone as well as in the elderly it may be useful to take melatonin, a tablet, 0.5 mg for jet lag and 1 mg for sleep disturbances, in the evening. Using melatonin for a short time is considered safe but side effects such as headaches or dizziness during the day can occur, while there are still no studies on long-term treatment with melatonin, so long term treatment related effects are unknown. Another recommendation is to avoid melatonin if you are suffering from mood disorders as it may cause depression or anxiety, or if you are taking medicines to control blood glucose and blood pressure, during pregnancy and breastfeeding. Remember to always ask your doctor for advice. Finally, many scientific studies are investigating the ability of melatonin to induce the death and proliferation of certain types of cancerous cells, we can mention Giuseppe di Bella's work of 2013 published on the International Journal of Molecular Sciences or the study published on the prestigious PLOS ONE magazine in 2014 about the ability of melatonin to reduce growth and proliferation of breast cancer by inhibiting angiogenesis. Other studies will follow to make more light on these melatonin properties.