If nighttime has you tossing and turning, you may be considering a dietary supplement to help you rest. Two popular choices are the amino acid glycine and magnesium glycinate, a form of the mineral magnesium that’s bonded to glycine, often to maximize effectiveness. Though both may be useful, experts say glycine has the edge for supporting sleep.

While magnesium glycinate supplements show promise for improving sleep, experts say there’s stronger scientific support for glycine as an effective sleep aid. 

“The evidence for glycine is stronger for helping you fall asleep, fall asleep more deeply, and wake up more awake the next day,” pulmonologist and sleep medicine specialist Emma Lin, MD, founder of Aimvein, told Health. “These studies involved real people, not just cells in a lab dish. They also looked at how well you slept, not just how stressed or moody you were.”

A 2023 research review, for example, found that, in seven out of eight studies, glycine was linked to improved sleep quality, alertness, and cognition, as well as decreased fatigue and sleepiness, in people who took 3 grams per day 30 minutes to one hour before bedtime over two to four days.

Glycine may even help make up for lack of sleep. In a 2012 paper, researchers deprived 10 healthy male volunteers of 25% of their usual sleep time for three nights but gave them 3 grams of glycine or a placebo before bed. Participants who took glycine reported significantly reduced daytime sleepiness and fatigue—a result confirmed by computer-based tests.

Glycine’s potential sleep-inducing ability has to do with its effects in the brain, explained sleep medicine physician William Lu, MD, medical director of Dreem Health, a digital sleep clinic. “Glycine acts as an inhibitory neurotransmitter and impacts NMDA receptors, which promote a calming, sleep-friendly, neural state of mind,” he said. “One of its most interesting effects is that it lowers core body temperature, which is a known signal for sleep onset.”

Magnesium glycinate, on the other hand, has neurological effects of its own—it “supports GABA signaling, regulates the stress response, and reduces cortisol activity,” Lu said. Lin pointed out that this form of magnesium also helps support muscle and nerve function—two important factors in healthy, restful sleep.

Not surprisingly, then, magnesium glycinate isn’t without some encouraging results—but the supplement appears to have more limited benefits, potentially offering support mainly for people who don’t get enough magnesium or have muscle tension, Lin said.

A 2025 study, for example, found that people with low dietary magnesium intake were more likely to see improved sleep quality than those with adequate intake after taking two capsules—about 900 milligrams—of magnesium glycinate 30 to 60 minutes before bed for a month.

The good news is that, according to Lu, most people don’t have to choose one supplement over the other. He advised consulting a doctor before starting new supplements so they can help guide the process, but said that “the two can usually be taken together as long as doses are started low and adjusted based on individual response.” 

As a general rule, Lu recommended starting with 1 gram of glycine 30 to 60 minutes before bedtime, then gradually increasing to 2 or 3 grams if you tolerate it well. Common side effects include digestive symptoms such as diarrhea, gas, or stomach pain.

For magnesium glycinate, a common starting point is 100 to 200 milligrams of elemental magnesium in the evening, he said. From there, you may choose to increase to the 200-300 mg range, depending on tolerance. “It’s best to increase slowly over several nights, pay attention to how you feel the next morning, and avoid exceeding typical upper supplemental ranges unless guided by a clinician,” Lu said.