NOW Foods L-Theanine Double Strength 200 mgvsNOW Foods Glycine Pure Powder

L-theanine is an amino acid found almost exclusively in tea leaves. It readily crosses the blood-brain barrier and increases alpha-wave activity, the brain pattern associated with relaxed wakefulness, while modulating the neurotransmitters GABA, serotonin, and dopamine. The result is a relaxed but clear-headed state that can lower the physiological and mental arousal that blocks sleep onset, which is why it is studied for both stress and sleep quality rather than as a sedative.

Glycine is both a building-block amino acid and an inhibitory neurotransmitter in the central nervous system. Taken before bed, research suggests it promotes peripheral vasodilation that lowers core body temperature - a physiological signal closely tied to sleep onset - and acts on NMDA receptors in the suprachiasmatic nucleus, the brain's master clock. The net effect in studies was faster sleep onset and improved sleep quality without altering overall sleep architecture.

A 2019 randomized, placebo-controlled crossover trial found that 200 mg/day of L-theanine for four weeks reduced anxiety and depression scores and improved Pittsburgh Sleep Quality Index subscales for sleep latency, sleep disturbance, and use of sleep medication in healthy adults. A 2025 systematic review of supplementation trials concluded L-theanine can improve some subjective sleep outcomes, and combination studies (for example with a milk-protein hydrolysate) have shown reduced sleep disturbance. Overall the effect is modest and primarily mediated through reduced stress and arousal rather than direct sedation.

The headline evidence is a 2007 study by Yamadera and colleagues in which 3 g of glycine before bed improved subjective sleep quality and shortened the time to fall asleep and to reach slow-wave sleep on polysomnography in people with unsatisfactory sleep; it also reduced daytime sleepiness and improved a memory task. Follow-up work from the same group reported reduced fatigue and better next-day performance after sleep restriction. The caveat is that these trials are small and largely from a single research program, so the evidence, while encouraging, is far from definitive.

L-theanine is among the best-tolerated supplements in this category, with side effects being uncommon and mild, such as occasional headache or stomach upset. Because it promotes relaxation, combining it with alcohol or sedative medications could be additive, so use judgment. This is educational information, not medical advice; individual results vary.

Glycine is exceptionally well tolerated because it is an amino acid the body already uses in large amounts; the most that sensitive users tend to report is mild stomach upset or soft stools at high intakes. As with any supplement, start at the studied dose rather than exceeding it. This is educational information, not medical advice; individual results vary.

Roughly $18-$24 for 120 capsules as of 2026, frequently discounted under $20, with a larger 180-count value size available. At one capsule daily that is months of supply for the price of a few coffees, and the product is often HSA/FSA eligible. Note the formula includes 100 mg of inositol, so it is not a single-ingredient product.

At about $29.99 list (and frequently under $25 at third-party retailers) for a 1 lb tub, and a studied dose of roughly 3 g, you get on the order of 150 bedtime servings - pennies per night. That makes glycine one of the lowest-cost ways to run a personal sleep experiment.

Adults whose sleeplessness is tied to stress, anxiety, or an overactive mind, or who want daytime calm without sedation. People who are pregnant or nursing, who take sedatives or blood-pressure medication, or who have a diagnosed anxiety or sleep disorder should consult a clinician. It is not a substitute for treatment of clinical insomnia.

Generally healthy adults curious about a low-risk sleep-quality aid. People who are pregnant or nursing, or who have a serious medical condition or take prescription medication, should consult a clinician first. It is not intended to treat diagnosed insomnia or any sleep disorder.