Can I Take Glycine with Dayvigo?

How Dayvigo and Glycine Each Promote Sleep

Dayvigo and glycine target sleep through separate pathways. Understanding where they overlap (and where they do not) clarifies why clinicians consider this combination relatively low-risk from a drug-interaction standpoint, while still advising caution around sedation.

Lemborexant: Blocking the Wake Signal

Lemborexant is a dual orexin receptor antagonist (DORA). Orexin-A and orexin-B are neuropeptides produced in the lateral hypothalamus that maintain wakefulness. By competitively binding OX1R and OX2R, lemborexant reduces wake drive rather than forcing sedation [1]. In the SUNRISE-1 trial (N=1,006), lemborexant 5 mg and 10 mg both significantly improved latency to persistent sleep and wake after sleep onset versus placebo in adults aged 55 and older [2].

The FDA approved lemborexant in December 2019 at doses of 5 mg and 10 mg taken within 5 minutes of bedtime [3]. Its half-life is approximately 17 to 19 hours, and it is metabolized primarily by CYP3A4 with minor contributions from CYP3A5 [1].

Glycine: An Inhibitory Neurotransmitter With Thermoregulatory Effects

Glycine acts as an inhibitory neurotransmitter in the brainstem and spinal cord. A 2015 study in Neuropsychopharmacology demonstrated that oral glycine (3 g before bed) lowered core body temperature via peripheral vasodilation and improved subjective sleep quality in volunteers with mildly impaired sleep (N=11) [4]. A separate randomized, single-blinded crossover study (N=19) found that 3 g of glycine before sleep reduced fatigue and improved daytime cognitive performance the following day [5].

Glycine does not undergo hepatic CYP-mediated metabolism. It is handled through normal amino acid metabolic pathways, including the glycine cleavage system in mitochondria [6]. This is the key reason a pharmacokinetic interaction with lemborexant is unlikely.

Is There a Direct Drug-Supplement Interaction?

No published case reports, pharmacokinetic studies, or FDA safety communications document a direct interaction between lemborexant and glycine. The interaction concern is pharmacodynamic, not pharmacokinetic.

Pharmacokinetic Analysis

Lemborexant depends on CYP3A4 for its primary metabolism. Strong CYP3A4 inhibitors (itraconazole, clarithromycin) significantly increase lemborexant exposure, which is why the prescribing information contraindicates co-administration with strong CYP3A4 inhibitors [1]. Glycine has no known CYP3A4 inhibitory or inductive activity. The Natural Medicines Comprehensive Database does not list a CYP-mediated interaction between glycine and any DORA-class drug [7].

Glycine absorption occurs through active transport in the small intestine (primarily via PAT1 and IMINO transporters). It does not compete with lemborexant for absorption, protein binding, or renal elimination [6].

Pharmacodynamic Analysis

Both agents promote sleep, but via unrelated mechanisms: orexin receptor blockade (lemborexant) and NMDA/glycine receptor modulation plus thermoregulation (glycine). When two substances both reduce wakefulness, their effects can be additive. This is the same principle behind the standard warning against combining Dayvigo with alcohol, benzodiazepines, or other CNS depressants [1].

The clinical significance of this additive effect with glycine is likely modest. Glycine at 3 g produces a mild, physiologic sleep-promoting effect, not the deep sedation seen with GABAergic agents. Still, individual variability exists. Some patients may notice greater morning grogginess when combining the two.

Dose Timing and Practical Guidance

Getting the timing right reduces the chance of excessive next-day sedation while preserving the sleep benefits of each agent. The goal is simple: avoid stacking peak effects unnecessarily.

When to Take Each Agent

Dayvigo should be taken within 5 minutes of going to bed, per its prescribing information [1]. Glycine (3 g) is typically taken 30 to 60 minutes before bed, based on the protocols used in published sleep studies [4][5]. This natural separation means glycine is already partially absorbed and beginning its thermoregulatory effect by the time lemborexant is ingested. No mandatory dose-separation window exists for this combination because there is no pharmacokinetic conflict, but this staggered approach is practical.

Starting Doses

If you are already stable on Dayvigo 5 mg, begin glycine at 3 g (the standard studied dose) and monitor for two to three nights before adjusting. If you are already taking glycine and starting Dayvigo for the first time, your prescriber will likely initiate lemborexant at 5 mg per FDA labeling [3]. Do not start both agents simultaneously if you have never tried either.

What to Watch For

Track these outcomes during the first week of combination use:

• Time to fall asleep (subjective)
• Number of awakenings
• Morning alertness on a 1 to 10 scale
• Any episodes of sleep-walking, sleep-driving, or complex sleep behaviors (rare but FDA-warned for all DORA agents [3])
• Daytime drowsiness, especially during the first four to six hours after waking

If morning grogginess persists beyond three or four days, discuss with your prescriber whether reducing glycine to 1.5 g or adjusting Dayvigo timing is appropriate.

Who Should Be More Cautious?

Most healthy adults tolerating Dayvigo monotherapy can add glycine without significant concern. Certain populations warrant closer attention.

Older Adults

The SUNRISE-1 trial enrolled adults 55 and older and found lemborexant 5 mg was well tolerated, with somnolence rates of 5% versus 1% for placebo [2]. Glycine's mild sedative profile is unlikely to create dangerous sedation in this group, but older adults have a higher baseline fall risk. Any additive drowsiness, even modest, increases that risk. A 2019 meta-analysis in The Lancet found that all hypnotic classes increased fall-related injury risk in adults over 65, with odds ratios ranging from 1.38 to 1.60 depending on drug class [8].

Patients on CYP3A4 Inhibitors

If you take a moderate CYP3A4 inhibitor (fluconazole, verapamil, diltiazem), your prescriber may have already lowered your Dayvigo dose to 5 mg maximum [1]. Adding glycine to an already-elevated lemborexant blood level means more total sleep-promoting effect. Inform your prescriber about all supplements, including glycine, at each visit.

Patients With Hepatic Impairment

Lemborexant exposure increases in moderate hepatic impairment (Child-Pugh B), and the drug is not recommended in severe hepatic impairment [1]. Glycine itself is not hepatotoxic, but the additive sedation on top of already-elevated lemborexant levels requires careful dosing. A prescriber may recommend starting glycine at 1.5 g rather than the standard 3 g.

Glycine's Evidence Base for Sleep

The evidence supporting glycine as a sleep aid is real but limited in scale. Recognizing the quality of this evidence helps set realistic expectations.

Published Trial Data

The most cited study is a 2006 randomized crossover trial (N=11) published in Sleep and Biological Rhythms, which found that 3 g glycine before bed improved subjective sleep quality and reduced next-day sleepiness [4]. A 2007 follow-up study (N=19) using polysomnography showed that glycine shortened the time to reach slow-wave sleep without altering total sleep architecture [5].

These are small studies. No phase III randomized controlled trial of glycine for insomnia exists.

Proposed Mechanisms

Glycine appears to lower core body temperature by 0.1 to 0.2°C through vasodilation, mimicking the natural thermoregulatory drop that precedes sleep onset [4]. It also acts on NMDA receptors in the suprachiasmatic nucleus, which may influence circadian signaling [9]. Neither of these mechanisms interferes with orexin receptor signaling, reinforcing the pharmacodynamic independence of glycine and lemborexant at the receptor level.

Other Supplement Roles of Glycine

Glycine is also used for collagen synthesis support (typically 5 to 15 g daily), blood sugar regulation, and neuroprotection research. Patients taking glycine at higher doses for non-sleep purposes (above 5 g) should flag this to their prescriber, as higher glycine doses may produce greater CNS inhibitory effects [6].

What If You Are Already Taking Both?

If you have been combining glycine and Dayvigo without issues, there is no clinical reason to stop either agent based on current evidence. Continue monitoring for next-day drowsiness and report any new symptoms.

When to Contact Your Prescriber

Reach out if you experience any of the following after adding glycine to your Dayvigo regimen:

• Daytime sleepiness that impairs driving or work performance
• New onset of sleep-related complex behaviors (cooking, walking, or driving while asleep)
• Confusion or disorientation upon waking
• Worsening of mood or depressive symptoms (lemborexant's label includes a suicidal ideation warning in patients with depression [1])

Adjustments a Clinician Might Make

A prescriber managing this combination may choose to reduce Dayvigo from 10 mg to 5 mg, reduce glycine from 3 g to 1.5 g, or stagger timing further. They will not typically need to order additional labs, since neither agent requires routine blood monitoring.

Glycine, Lemborexant, and Other Common Supplements

Patients taking Dayvigo often ask about stacking multiple sleep-support supplements. Here is how glycine fits alongside the most common ones.

Melatonin

Melatonin (0.5 to 5 mg) and glycine work through different pathways (MT1/MT2 receptor agonism versus thermoregulation/NMDA modulation). Adding both to Dayvigo creates a three-agent sleep stack. No published data support or refute this specific triple combination. The additive sedation risk increases with each agent added. Discuss with your prescriber before combining all three.

Magnesium

Magnesium glycinate is a common sleep supplement that already contains glycine as the chelating amino acid. A typical magnesium glycinate dose (400 mg elemental magnesium) provides roughly 2.4 g of glycine. Patients taking both standalone glycine and magnesium glycinate may inadvertently consume 5+ g of glycine nightly. This is not dangerous but may increase sedation. Account for the glycine content in your magnesium supplement when calculating total glycine intake [10].

L-Theanine

L-theanine (100 to 200 mg) promotes relaxation via alpha-wave enhancement without direct sedation. It does not interact with CYP3A4 and has no known interaction with lemborexant. Combined with glycine and Dayvigo, it adds a fourth sleep-related agent. The more agents stacked, the harder it becomes to identify which is causing side effects. Simplicity is better.

The Bottom Line on Safety

The glycine-Dayvigo combination carries low pharmacokinetic risk and moderate pharmacodynamic risk from additive sedation. No FDA warning, formal contraindication, or published adverse event report exists for this pair. The standard glycine dose for sleep (3 g) is the best-studied dose and a reasonable starting point for patients already stable on lemborexant 5 mg or 10 mg.

Track morning alertness during the first week of combined use. Patients over 65, those on CYP3A4 inhibitors, or those with hepatic impairment should start glycine at 1.5 g and titrate. Report any complex sleep behaviors immediately.