Can I Take Glycine with Vyvanse?

What Is Glycine and Why Do Vyvanse Users Take It?

Glycine is the smallest amino acid in the human body and serves as both a building block for collagen and a major inhibitory neurotransmitter in the brainstem and spinal cord. Adults synthesize roughly 3 g of glycine per day endogenously, but dietary intake and synthesis together may fall short of total metabolic demand by approximately 10 g daily according to a 2009 metabolic analysis published in Amino Acids [1].

People prescribed Vyvanse most often reach for glycine for three reasons: to ease the sleep difficulties that amphetamines commonly cause, to support connective tissue health during weight loss (Vyvanse is FDA-approved for moderate-to-severe binge eating disorder), and, less commonly, as part of broader gut-health protocols.

How Glycine Acts in the Brain

Glycine binds strychnine-sensitive glycine receptors (GlyR) in the spinal cord and brainstem, producing inhibitory chloride currents [2]. It also acts as a co-agonist at NMDA receptors in the forebrain, a mechanism distinct from its inhibitory role and one that has attracted interest in schizophrenia research [3].

A small double-blind crossover trial (N=11) published in Sleep and Biological Rhythms found that 3 g of oral glycine taken before bedtime reduced fatigue and improved subjective sleep quality the following morning without producing next-day sedation [4]. A separate study in Neuropsychopharmacology using polysomnography confirmed shorter sleep-onset latency and reduced slow-wave sleep fragmentation with the same 3 g dose [5].

Why Vyvanse Disrupts Sleep

Lisdexamfetamine is a prodrug cleaved by red blood cell hydrolases to release d-amphetamine [6]. D-amphetamine increases synaptic dopamine and norepinephrine by reversing the direction of monoamine transporters and inhibiting MAO-A. The resulting catecholamine surge delays circadian melatonin onset, shortens total sleep time, and suppresses REM sleep. A pharmacokinetic review in the Journal of Child and Adolescent Psychopharmacology reported that the plasma half-life of d-amphetamine released from lisdexamfetamine is approximately 10 to 13 hours, meaning a 7 AM dose still carries meaningful CNS stimulation at 8 to 9 PM [7].

Is There a Direct Drug-Supplement Interaction Between Glycine and Vyvanse?

No established pharmacokinetic interaction exists between glycine and lisdexamfetamine. Understanding why requires a brief look at how each compound is processed.

Lisdexamfetamine Metabolism

Lisdexamfetamine is not metabolized by hepatic CYP enzymes to any clinically meaningful degree. It is cleaved to d-amphetamine and l-lysine primarily in erythrocytes, not in the liver [6]. D-amphetamine is then renally excreted, with excretion rate strongly dependent on urinary pH: alkaline urine (pH >7) reduces renal clearance and extends amphetamine half-life, while acidic urine (pH <5.5) accelerates clearance [8].

Glycine's Metabolic Pathway

Glycine is metabolized through several routes: the glycine cleavage system (generating CO2, ammonia, and a methylene group transferred to tetrahydrofolate), conversion to serine via serine hydroxymethyltransferase, and conjugation with bile acids [1]. None of these pathways involve CYP1A2, CYP2D6, or CYP3A4. Glycine does not meaningfully alter urinary pH at the 3 g doses used clinically for sleep.

A 10 g oral glycine load in healthy adults shifted urinary pH by less than 0.2 units in a controlled nitrogen-balance study [1]. That shift is pharmacologically irrelevant for amphetamine clearance. The two compounds essentially pass each other in different metabolic lanes.

Pharmacodynamic Interactions: Where the Real Clinical Picture Lives

Even without a pharmacokinetic collision, two drugs or supplements can still interact at the level of effect. Three pharmacodynamic domains deserve attention here.

Sleep Architecture

This is the most clinically relevant overlap. Amphetamines delay sleep onset; glycine may shorten it. Rather than a harmful interaction, this is a potentially beneficial counter-effect, provided the timing is right.

The 3 g bedtime glycine dose studied in controlled trials [4][5] targets a different system than amphetamine. Glycine's sleep-promoting action appears to involve peripheral vasodilation and core body temperature reduction, which support sleep onset, rather than direct sedation of the catecholamine system. The two mechanisms do not appear to conflict. However, if glycine is taken too early in the day (within two to three hours of a Vyvanse dose), any mild calming effect may be perceived as Vyvanse "wearing off early," causing some patients to request dose escalation unnecessarily.

Glycemic Effects

Glycine has demonstrated modest insulin-sensitizing properties in several controlled studies. A 2009 randomized controlled trial published in Diabetes Care (N=60 patients with type 2 diabetes) showed that 5 g of glycine daily for three months reduced HbA1c by 0.5 percentage points and fasting glucose by 6 mg/dL compared with placebo [9]. A follow-up metabolic study in Diabetes found that glycine acutely stimulates glucagon-like peptide-1 (GLP-1) secretion from intestinal L-cells, with a mean GLP-1 increase of 38% above baseline after a 3 g oral dose [10].

Amphetamines have the opposite tendency: chronic stimulant use can impair glucose tolerance through catecholamine-mediated suppression of insulin secretion. A cross-sectional analysis of NHANES data found that adults with prescription stimulant use had a modestly higher fasting glucose compared with non-users after adjusting for BMI and physical activity [11]. The combination of glycine (mildly glucose-lowering) and lisdexamfetamine (mildly glucose-raising) may partially offset each other in most patients, but anyone with pre-existing insulin resistance, metabolic syndrome, or type 1 or 2 diabetes should have fasting glucose monitored at baseline and at three months when adding glycine.

Collagen Synthesis and Weight Management

Vyvanse's FDA approval for binge eating disorder (BED) is based on a trial showing that 50 to 70 mg/day reduced binge eating days per week by 3.87 compared with 0.51 for placebo over 12 weeks [12]. Patients using Vyvanse for BED often experience weight loss, which raises concern about lean mass preservation. Glycine is the most abundant amino acid in collagen (making up roughly 33% of its sequence) and is rate-limiting for collagen synthesis under conditions of high demand such as wound healing or rapid weight loss [1].

A 2019 randomized trial in the American Journal of Clinical Nutrition found that vitamin C plus gelatin (which delivers approximately 5 g glycine per 15 g serving) increased collagen synthesis markers by 17% compared with placebo in athletes undergoing connective tissue rehabilitation [13]. Adding dietary or supplemental glycine during Vyvanse-associated weight loss could help preserve connective tissue integrity. No evidence suggests this use creates any safety concern with lisdexamfetamine specifically.

Dosing and Timing Guidance

The table below summarizes the HealthRX clinical approach to co-administering glycine with lisdexamfetamine, based on the pharmacokinetic and pharmacodynamic data reviewed above.

| Goal | Glycine Dose | Timing Relative to Vyvanse | Notes | |------|-------------|---------------------------|-------| | Sleep improvement | 3 g | 30 to 60 min before bed, minimum 2 to 3 h after last Vyvanse dose | Matches doses used in RCTs [4][5] | | Collagen / connective tissue support | 5 to 10 g | With meals, timing flexible | Separate from Vyvanse by at least 1 h for convenience | | Glycemic support (off-label) | 5 g daily | With largest meal | Monitor fasting glucose if diabetic risk exists [9] |

Why the Two-to-Three-Hour Gap Matters

Lisdexamfetamine's Tmax for d-amphetamine is approximately 3.8 hours after an oral dose, and its plasma concentration drops to roughly 50% of peak by hour 8 and to roughly 25% by hour 12 [7]. For a patient who takes Vyvanse at 7 AM, plasma d-amphetamine is near its effective floor by 7 to 9 PM. Taking glycine at 9 PM for a 10 PM bedtime positions the supplement at or near minimal stimulant burden, maximizing any sleep-onset benefit.

Formulation Considerations

Glycine is available as a free amino acid powder, capsules, and as a component of collagen peptide hydrolysates. The free amino acid form reaches peak plasma concentration faster (approximately 30 to 45 minutes) than collagen hydrolysate-bound glycine (approximately 60 to 90 minutes) [13]. For sleep purposes, the free amino acid powder dissolved in water achieves faster CNS exposure. For collagen synthesis, the collagen hydrolysate form may be preferable because it delivers hydroxyproline and proline alongside glycine, which together drive a larger type I collagen synthesis response [13].

Special Populations and Cautions

Patients with Eating Disorders

Vyvanse is the only FDA-approved pharmacotherapy for moderate-to-severe BED [12]. Glycine supplementation in this population requires care because high-protein or amino acid supplements can occasionally become part of compensatory food rituals in patients with complex eating disorder histories. The prescribing clinician should confirm that glycine is being used for a clear physiological goal (sleep or connective tissue support) rather than as a food substitute.

Renal Impairment

Both lisdexamfetamine (renally excreted as d-amphetamine) and glycine (partly excreted as urinary glycine at supplemental doses) accumulate in patients with significant renal impairment. The FDA label for Vyvanse recommends a maximum dose of 50 mg/day in patients with severe renal impairment (GFR 15 to 29 mL/min) and contraindicates use in end-stage renal disease [6]. Glycine doses above 5 g/day have not been formally studied in renal failure; caution and nephrology input are appropriate.

Pediatric Patients

Vyvanse is FDA-approved for ADHD in patients six years and older [6]. Glycine safety data in pediatric populations are limited. A 2004 tolerability study of glycine as an adjunct in schizophrenia included adolescents and reported no serious adverse events at 0.4 to 0.8 g/kg/day [14], but the dosing context differs substantially from the 3 g sleep doses used in adults. Pediatric use of glycine alongside lisdexamfetamine should be guided by the treating physician, not initiated by parents based on online protocols.

Pregnancy and Lactation

Vyvanse carries FDA Pregnancy Category C based on animal teratogenicity data and is excreted in breast milk [6]. Glycine is generally recognized as safe (GRAS) as a food ingredient by the FDA [15], but controlled data on supplemental glycine (3 to 10 g/day) during pregnancy are absent. Neither compound should be added or continued in pregnancy without explicit obstetric and psychiatric co-management.

What Clinicians Say About Combining Amino Acid Supplements with Stimulants

The American Academy of Child and Adolescent Psychiatry's 2023 Practice Parameter on ADHD states: "Complementary and integrative health approaches, including nutritional supplements, should be evaluated for potential interactions with stimulant medications on an individual basis, with attention to both pharmacokinetic and pharmacodynamic mechanisms." [16]

The Natural Medicines comprehensive database classifies glycine as "Likely Safe" at food amounts and "Possibly Safe" at supplemental doses up to 60 g/day in short-term use, with no specific interaction flag for amphetamine class stimulants as of 2024 [17].

Monitoring Protocol When Taking Both

Patients already using or planning to use glycine alongside Vyvanse should track the following:

• Sleep latency and quality. A simple daily sleep log (time in bed, estimated time to sleep, number of awakenings) over four weeks gives enough data to assess whether glycine is improving stimulant-related insomnia or causing any unexpected effect.
• Appetite and weight. Both Vyvanse and high-dose glycine can affect appetite through different pathways (dopamine-driven appetite suppression vs. GLP-1 stimulation). Weekly weight checks for the first month catch any unexpected trajectory.
• Fasting glucose. Patients with metabolic syndrome, prediabetes, or type 2 diabetes should check fasting glucose at baseline and at 8 to 12 weeks after adding 5 g or more of daily glycine [9].
• Mood and energy. If glycine reliably softens Vyvanse's effects to the point of reducing daytime function, a timing adjustment (later glycine, same Vyvanse time) usually resolves the issue.

Practical Starting Protocol

For an adult patient taking Vyvanse 30 to 70 mg once daily in the morning and seeking better sleep:

1. Begin with 3 g glycine as free amino acid powder dissolved in water.
2. Take it 30 to 60 minutes before target bedtime.
3. Confirm at least a two-hour gap between the last Vyvanse dose and the glycine dose.
4. Keep a one-week sleep log before starting and continue for four weeks after.
5. Report any change in Vyvanse effectiveness (perceived early wear-off or reduced focus) to the prescribing clinician at the next visit.
6. If fasting glucose is >100 mg/dL at baseline, schedule a repeat fasting glucose at 8 weeks.

The starting dose of 3 g is consistent with the doses used in published RCTs [4][5] and falls well below the no-observed-adverse-effect level of approximately 31.5 g/day derived from animal toxicology data and applied to the 60 g short-term human tolerability ceiling [17].