If you're among the millions of Americans desperate for a good night's sleep, you may have tried an over-the-counter sleep aid. Common ones include medications that contain diphenhydramine (e.g., Unisom, Zzzquil, Tylenol/Advil PM), an antihistamine also found in allergy medications like Benadryl. Diphenhydramine is a sedative, which many of us have realized after taking it for allergies and then feeling knocked out at work.

Another very common OTC medication that's often taken for insomnia is melatonin. About half of the people who come to me for insomnia treatment are taking melatonin, which suggests that at least for these individuals, it's not a very effective treatment for insomnia.
In fact, the most recent meta-analysis of studies in this area found that melatonin supplements provide about 8 minutes additional sleep per night compared to placebo. If you're starved for sleep, anything beats nothing, but for many people 8 minutes is just a drop in the bucket. To understand why the effect is so small, let's consider what melatonin is and how it's related to sleep.

What Is Melatonin?

Your body produces the hormone melatonin in the pineal gland, a small structure that sits just above the brainstem at the midline of the brain (see figure). The pineal gland is controlled by a center within the hypothalamus—the suprachiasmatic nucleus—that regulates our circadian rhythm.
Thanks to this roughly 24-hour cycle, our major bodily functions like sleeping, waking, body temperature, hormones, and metabolism are aligned with the cycles of light and dark, as well as with all the activities that coincide with day and night. If you've ever been jet lagged, you know how disruptive it is to have your internal cycle and external demands misaligned.
The timing of melatonin release is consistent with its relation to sleep: Very little melatonin is released during the day, with levels rising as the sun goes down and bedtime approaches. Melatonin levels peak in the middle of the night, and fall to their daytime lows as we approach our wakeup time (and the sky begins to lighten).
Given the increase in melatonin as sleep approaches, it's reasonable to expect that taking extra melatonin would facilitate sleep—especially at the high doses of 3, 5, or even 10 mg often sold in US drug stories (several research studies on melatonin used doses of .1 or .3 mg). So why only 8 minutes of additional sleep?

Role of Melatonin in Sleep

In humans, who generally sleep at night, melatonin levels rise after sunset. In rodents and other vertebrates that are active at night, melatonin levels also rise at night. That's right: The same hormone is linked to opposite patterns of behavior, depending on the species.

For example, when researchers continuously measured melatonin levels in mice, they found a strong connection between higher melatonin levels and greater activity. 

So what melatonin actually seems to be doing is sending a signal for "typical nighttime behavior." If you're a human or other "diurnal" (active during the day) species, that signal will mean "go to sleep." For a mouse, that same signal means to sneak into your kitchen and forage for food. And if you battle chronic insomnia, your typical nighttime behavior might be staring at the ceiling and praying for sleep.
No wonder melatonin doesn't tend to be a great sedative. It's not like an antihistamine or a benzodiazepine that have inherently tranquilizing effects—that's not its function. Instead the role of melatonin is to match our internal clocks with external demands, particularly those aligned with light-dark schedules.

Recommended Treatments

In light of (no pun intended) the limited evidence for melatonin's effectiveness as a sleep aid, current clinical guidelines recommend against its use in the treatment of chronic insomnia. These guidelines list other types of medication (e.g., zolpidem, eszopiclone; trade names Ambien, Lunesta) that may be better options based on their demonstrated efficacy.
The guidelines also recommend that any medication be paired with a treatment like cognitive behavioral therapy for insomnia (CBT-I). While some medications can be as effective as CBT-I in the short term, CBT-I has a better track record for helping in the long term, even without medication. 

Unfortunately the best therapies are often the hardest to find. If you don't have a CBT-I expert close to you or in your insurance network, there are other options available so you can still have the benefit of this treatment.

One option is to use a CBT-I app. One of the benefits of an app is that it can make it easier to record and analyze your sleep data, an essential part of the treatment. While I can't personally vouch for any of these applications, this review provides a helpful summary of some of the available options.
There are also books available that present CBT-I; two that have gotten good reviews are End the Insomnia Struggle and Quiet Your Mind and Get to Sleep.
So while melatonin won't cure most people's insomnia, there are other options that can be very effective, and in the case of CBT-I involve no medications or related side effects.

Melatonin for Shifting Sleep Schedule

While melatonin is not recommended for treating insomnia, the American Academy of Sleep Medicine does include it in its treatment guidelines for some of the sleep conditions related to circadian rhythm—consistent with its physiological function.
For example, many people experience "Advanced Sleep-Wake Phase Disorder," which simply means they're extreme night owls. In combination with other components like bright light at specific times, carefully scheduled melatonin can help shift one's circadian rhythm to better align with work and school schedules.

Care needs to be taken with the timing of melatonin supplements—too early or too late and it can exacerbate the problem. Working with a specialist in behavioral sleep medicine generally is required.
If you've considered treatment for insomnia or another sleep disorder, now might be a good time to look into it. Better sleep helps with pretty much everything.