Can I Take Glycine with Lunesta (Eszopiclone)?

What Kind of Interaction Exists Between Glycine and Eszopiclone?

The interaction is pharmacodynamic, not pharmacokinetic. Glycine does not meaningfully alter the absorption, distribution, metabolism, or excretion of eszopiclone. Instead, both agents work through separate but overlapping pathways that converge on reducing the time it takes to fall asleep and increasing total sleep time. That overlap is where the clinical concern lives.

How Eszopiclone Works

Eszopiclone is the S-enantiomer of zopiclone. It binds selectively to the benzodiazepine site of the GABA-A receptor, potentiating chloride influx and producing sedation, anxiolysis, and muscle relaxation [1]. The FDA label for Lunesta notes that its half-life is approximately 6 hours, with peak plasma concentration reached within 1 hour of an oral dose [2]. Because eszopiclone is primarily metabolized by CYP3A4, co-administration of strong CYP3A4 inhibitors (such as ketoconazole) can nearly double its exposure [2].

How Glycine Works as a Sleep Aid

Glycine (aminoacetic acid) is the simplest amino acid and acts as an inhibitory neurotransmitter in the spinal cord and brainstem via glycine receptors, as well as an NMDA receptor co-agonist in the brain [3]. At a 3 g oral dose, glycine lowers core body temperature by roughly 0.3 degrees Celsius through peripheral vasodilation, a mechanism that mirrors the natural temperature drop that precedes sleep onset [4]. In a placebo-controlled crossover trial by Bannai et al. (N=11), 3 g of glycine taken before bed significantly reduced fatigue and sleepiness the following day (P<0.05) without altering sleep architecture on polysomnography [4].

Why the Overlap Matters Clinically

Both agents converge on the same physiological endpoint, namely, faster sleep onset and deeper slow-wave sleep. Adding glycine to an established eszopiclone regimen may intensify next-morning sedation, which the FDA label already lists as a risk even with eszopiclone alone [2]. The 2023 American Academy of Sleep Medicine clinical practice guidelines note that residual sedation from hypnotic agents is associated with increased fall risk in adults over 60 [5].

Does Glycine Affect How the Body Processes Eszopiclone?

No clinically meaningful pharmacokinetic interaction has been documented. This distinction matters because it tells you which part of the drug-supplement relationship to monitor.

Eszopiclone's Metabolic Pathway

Eszopiclone undergoes hepatic oxidation primarily via CYP3A4 and, to a lesser extent, CYP2E1, producing two main metabolites: (S)-zopiclone N-oxide (weakly active) and (S)-N-desmethylzopiclone (inactive) [1,2]. Strong CYP3A4 inhibitors raise eszopiclone AUC by up to 2.2-fold; strong inducers reduce it substantially [2].

Glycine's Metabolic Footprint

Glycine is metabolized through several pathways: transamination, the glycine cleavage system (GCS), conversion to serine via serine hydroxymethyltransferase, and conjugation with bile acids [3]. None of these pathways involve CYP3A4 or CYP2E1 in a clinically significant way. A 2019 review in Nutrients covering amino acid-drug interactions found no documented CYP enzyme inhibition or induction for glycine at supplemental doses up to 10 g/day [6]. This means glycine is unlikely to raise or lower eszopiclone blood levels.

What Could Still Go Wrong Pharmacokinetically

The one indirect pharmacokinetic concern is gastric emptying. High-protein meals or large amino acid loads can slow gastric motility, which may slightly delay eszopiclone's peak plasma concentration. The Lunesta prescribing information already cautions that a heavy, high-fat meal slows absorption and reduces peak plasma concentration by roughly 20% [2]. A 3 g glycine dose is unlikely to replicate a high-fat meal's effect, but taking glycine dissolved in a large volume of fluid along with eszopiclone could theoretically blunt the hypnotic's speed of onset very mildly.

What Are the Real Risks of Combining Glycine and Lunesta?

The practical risks sit in three categories: excess sedation, psychomotor impairment, and glycemic effects in specific populations.

Additive Sedation and Next-Morning Impairment

Eszopiclone 3 mg already produces measurable psychomotor impairment approximately 7.5 hours after a bedtime dose in healthy adults, according to a pharmacodynamic study published in Sleep Medicine [7]. Glycine at 3 g did not impair psychomotor function in the Bannai trial, but that trial did not test glycine on top of an existing hypnotic [4]. The FDA's 2013 safety communication on sedative-hypnotics specifically warns against combining these agents with other CNS depressants because of additive next-morning impairment affecting driving [8]. Glycine's mild sleep-promoting effect could tip a borderline patient into clinically significant morning-after drowsiness.

Falls in Older Adults

Adults 65 and older are already at higher fall risk on eszopiclone. The American Geriatrics Society 2023 Beers Criteria lists all non-benzodiazepine receptor agonists (including eszopiclone) as medications to avoid in older adults because the risk of falls and fractures outweighs the benefit in this population [9]. Adding a second sleep-promoting agent, even a gentle amino acid, increases that risk profile.

Glycemic Considerations

Glycine has modest insulin-sensitizing properties. A randomized controlled trial by Gannon et al. (N=9) found that 5 g of glycine reduced postprandial blood glucose in healthy subjects [10]. Eszopiclone itself has been associated with small increases in fasting glucose in some observational data, though the causal relationship is debated. For patients with type 2 diabetes or prediabetes taking both glycine and a sedative hypnotic, blood glucose monitoring deserves attention, particularly in the early weeks of combined use.

Dose Timing: How to Separate Glycine and Eszopiclone if Your Physician Approves Combined Use

If a physician determines that concurrent use is appropriate, timing and dosing discipline reduce the overlap in sedative peak effects. The framework below reflects available pharmacokinetic data rather than a specific published protocol, since no head-to-head combination trial exists.

Suggested Timing Window

Eszopiclone reaches peak plasma concentration (Tmax) within 1 hour of an oral dose taken on an empty stomach [2]. Glycine reaches peak serum levels in approximately 30 to 45 minutes after a 3 g oral dose dissolved in water [4]. Taking both simultaneously means both peaks coincide. One rational option, pending physician guidance, is to take glycine 45 to 60 minutes before the eszopiclone dose. This allows glycine's temperature-lowering effect to initiate sleep pressure naturally, potentially permitting use of the lowest effective eszopiclone dose (1 mg).

Starting Doses

The approved starting dose of eszopiclone is 1 mg immediately before bed, with titration to 2 or 3 mg only if clinically necessary [2]. The evidence-backed glycine dose for sleep is 3 g; going above this has not shown additional sleep benefit in published trials [4]. Neither agent should be dose-escalated without a prescriber's input.

What to Track

Keep a simple sleep diary for the first two weeks of combined use. Record time to fall asleep, total sleep time, and how alert you feel at 8 AM. If morning alertness scores drop or you feel sedated while driving, contact your prescriber immediately. Do not self-adjust the eszopiclone dose.

Who Should Not Combine Glycine and Eszopiclone?

Certain populations face disproportionate risk.

Strong CYP3A4 Inhibitor Users

Patients already taking a strong CYP3A4 inhibitor (azole antifungals, some macrolide antibiotics, ritonavir) will have significantly elevated eszopiclone plasma levels. The Lunesta label recommends not exceeding 2 mg in these patients [2]. Adding glycine on top of already-elevated eszopiclone exposure compounds the sedation risk without offering additional pharmacokinetic interaction data to guide dosing.

Patients on Multiple CNS Depressants

Opioids, benzodiazepines, muscle relaxants, antihistamines, and alcohol all increase CNS depression. The FDA's 2016 black box warning on sedative-hypnotics used with opioids applies directly here [8]. Glycine in this context adds one more layer of sedation. Even a small additive effect in this population can tip clinical status toward respiratory depression.

Pregnant and Breastfeeding Women

Eszopiclone is FDA Pregnancy Category C (animal studies show risk, no adequate human data) [2]. Glycine supplementation in pregnancy lacks strong safety data at doses above dietary intake. Neither the American College of Obstetricians and Gynecologists nor the AASM has issued guidance endorsing supplemental glycine for sleep during pregnancy [5]. Avoid the combination unless a physician has weighed the specific clinical situation.

Older Adults (65 and Over)

As noted above, the Beers Criteria recommendation against eszopiclone in older adults is explicit [9]. Adding glycine does not resolve this concern.

What Does the Evidence Base Look Like? Gaps and Limitations

The honest answer is that no published randomized controlled trial has directly studied glycine co-administered with eszopiclone. The available evidence is composed of individual mechanistic studies on each agent separately, pharmacokinetic modeling, and case-level clinical reasoning.

Evidence for Glycine Alone

The Bannai et al. 2012 crossover trial (N=11) remains the most-cited human study on glycine for sleep [4]. A follow-up study by the same group published in Frontiers in Neurology (2012) replicated the findings in a slightly larger sample and confirmed reduced daytime sleepiness via the Karolinska Sleepiness Scale [11]. Both trials used 3 g of glycine and were conducted in subjects who were not taking any prescription hypnotics.

Evidence for Eszopiclone Alone

Eszopiclone's efficacy in insomnia is well established. A 6-month randomized controlled trial by Krystal et al. (N=788) published in Sleep demonstrated that eszopiclone 3 mg improved sleep latency, wake time after sleep onset, and total sleep time compared to placebo across the full study duration [12]. This remains one of the longest-duration hypnotic RCTs and formed part of the basis for the FDA approval.

The Combination Gap

No combination trial exists in PubMed as of January 2025. The Natural Medicines Database rates the interaction as "unknown" owing to insufficient evidence, not because evidence of safety has been established. An unknown rating should be treated as a caution, not a clearance.

Monitoring Recommendations if You Are Already Taking Both

Some patients may already be combining glycine powder with their Lunesta prescription before finding this article. Here is a practical monitoring checklist.

Short-Term (First 14 Days)

Check morning alertness daily using a simple 1-to-10 self-rating. Rate your ability to drive, focus, or operate equipment. Any score below 6 warrants a same-day call to your prescriber. Log any new symptoms: unusual vivid dreams, sleepwalking episodes, or morning confusion. These are known side effects of eszopiclone alone and may intensify with added sleep-promoting agents [2].

Medium-Term (Weeks 2 Through 8)

If you have type 2 diabetes or take medications for blood sugar, add a fasting glucose check once weekly for the first 8 weeks. Glycine's insulin-sensitizing effects, while modest, are real [10]. Consider discussing a gradual eszopiclone dose reduction with your prescriber, since the glycine may be offering meaningful sleep support on its own.

When to Stop Immediately

Stop glycine and contact your prescriber the same day if you experience: an episode of sleepwalking or sleep driving (a documented risk with sedative-hypnotics) [8]; marked confusion on waking; a fall during the night; or a blood glucose reading below 70 mg/dL without another explanation.

Practical Clinical Summary for Patients and Prescribers

Glycine at 3 g is a low-risk supplement for most healthy adults. Eszopiclone at 1 to 3 mg is a prescription CNS depressant with a documented next-morning impairment profile. Their combination produces additive sleep-promoting and sedative effects through complementary but distinct mechanisms. No pharmacokinetic interaction via CYP enzymes has been documented. The primary concern is pharmacodynamic: combined use may deepen and lengthen sedation beyond what either agent produces alone.

For prescribers evaluating this combination, the most conservative approach is to start eszopiclone at 1 mg when a patient is already using 3 g glycine nightly, rather than the standard 2 mg starting dose, and titrate only if clinically necessary. For patients who want to add glycine to an established eszopiclone regimen, discuss the plan with the prescriber, start glycine at 3 g (not higher), take it 45 to 60 minutes before eszopiclone, and track morning alertness for two full weeks.

The lowest effective dose of eszopiclone that achieves the therapeutic goal remains the target [2].