Melatonin is a hormone produced by the pineal gland that induces sleep. Many people are now taking it in supplemental form to help sleep on a nightly basis. I don't think this is the best approach. There are many other things they can do to induce a good nights sleep and I think it is best to save the use of melatonin supplementation for when you are jet-lagged or change shifts at work for example.
It is important to understand that melatonin helps shorten the time to fall asleep but has little to no effect on deep sleep and the rapid eye movement phases. This is why I think it is best used as a supplement to help reset your circadian rhythm. Again the key word is "supplement". Getting a lot of morning sunlight, exercising, eating your last meal before 6pm, blocking blue light of a night, and keeping a regular wake time and bed time, for example, are more powerful than taking a melatonin supplement to help re-set your circadian rhythm and induce a good nights sleep. If you do these on a daily basis then you will not need to supplement with melatonin. Save it for an emergency.
Melatonin relaxes your muscles and nerves which makes your sleep better. The anti-spasmodic effect also helps the intestinal tract, relaxing it when it is contracted and tense. Recently it has been shown to help with GERD as Michael Jergelwicz DC, DACBN, DCBCN, CNS points out "Large amounts of melatonin are found in tissues of the GI tract that are continuously exposed to a hostile environment. One of the main functions of melatonin produced by the GI tract is to protect the esophageal and gastric mucosa from stressors and irritants. Previous research has demonstrated remission of GERD symptoms from melatonin supplementation comparable to PPIs.
Melatonin is a potent antioxidant that can influence all major functions of the GI tract, including secretion, motility, digestion and intestinal absorption. It has an inhibitory influence on gastric acid secretion resulting in an increase in gastrin release, which increases the contractile activity of the lower esophageal sphincter and reduces the symptoms of GERD."
So melatonin actually has many benefits other than just inducing sleep. It is a strong antioxidant which helps protect against free radicals, it can increase serum levels of growth hormone, and also thyroid hormones by increasing the conversion of T4 into the more active T3, and can calm down cortisol levels.
When taking melatonin, start with a small dose. If you sleep good for the first few hours but then wake up and can't get back to sleep, or wake up with a heavy head the next morning, you more than likely have to cut back your dose.
Getting a quality brand is important as it is with anything. Matthew Walker explained that evaluations of over the counter brands found melatonin concentrations that range from 83% less than that claimed on the label, to 478% more that that stated.
Taking a sublingual product is also something to consider. This is what Dr Hertoghe recommends as it is more quickly absorbed into the bloodstream, it is more reliably absorbed than the oral form, and because of this you need a smaller dose.
Use melatonin supplements for stressful times such as jet-lag or a change in shift at work
Get out in the sun. Expose the eyes to morning sunlight and get out in the brightest part of the day. Take a walk at you lunch break.
Exercise during the day. If not training in the gym do your intervals outside, tie this in with the above.
Relax during the evening. Set yourself up for sleep. Block blue light, get off electrical devices, do some meditation, journalling, or stretching.
Make your bedroom pitch black and remove all electronics.
Wake up at the same time every day.