Can I Take Glycine with Accutane (Isotretinoin)?

What Is Glycine and Why Do Accutane Patients Ask About It?

Glycine is the simplest amino acid in the human body and functions as both a building block for proteins and a direct inhibitory neurotransmitter in the spinal cord and brainstem. Patients on isotretinoin often search for glycine because of three overlapping concerns: disrupted sleep from the drug's systemic retinoid effects, the desire to support collagen while sebaceous gland activity is suppressed, and general interest in liver-protective strategies during a course that requires mandatory hepatic monitoring.

Isotretinoin (13-cis-retinoic acid) is approved by the FDA for severe recalcitrant nodular acne and is dispensed exclusively through the iPLEDGE risk management program in the United States [1]. Its mechanism involves binding to nuclear retinoid receptors, reducing sebocyte proliferation and normalizing follicular keratinization [2].

Why Patients Layer in Supplements

Accutane courses typically run 16 to 24 weeks at cumulative doses of 120 to 150 mg/kg. During that window, patients frequently experience dryness, joint discomfort, and sleep disturbance. Glycine has drawn interest because it is inexpensive, widely available, and carries a well-established safety record at doses studied in humans up to 9 g per day [3].

How Glycine Is Absorbed and Used

After oral ingestion, glycine is absorbed rapidly in the small intestine via sodium-coupled transporters and enters the portal circulation within 30 to 60 minutes. It is then directed into one-carbon metabolism, collagen synthesis, glutathione production, and bile acid conjugation. None of these pathways depend on cytochrome P450 3A4, 2C8, or 2C9, the primary enzymes involved in isotretinoin oxidation [4].

Pharmacokinetic Interaction: Is There One?

No pharmacokinetic interaction between glycine and isotretinoin has been identified in the published literature. The two compounds do not share metabolic enzymes, plasma protein binding sites, or renal transport systems in any documented way.

Isotretinoin is highly protein-bound (greater than 99%) and is metabolized primarily to 4-oxo-isotretinoin and retinoic acid via CYP2C8 and CYP3A4 [4]. Glycine does not inhibit or induce these enzymes at physiologic or supplemental concentrations. A 2014 review in Drug Metabolism and Disposition confirmed that simple amino acids lack meaningful CYP-inhibitory activity at doses achievable through dietary or supplemental intake [5].

What Pharmacodynamic Overlap Might Exist

Pharmacodynamic concerns are more relevant here than pharmacokinetic ones, though still modest. Three areas are worth examining: hepatic enzyme activity, glucose metabolism, and collagen support.

Glycine and Isotretinoin Liver Safety

Isotretinoin raises alanine aminotransferase (ALT) in roughly 10 to 15% of patients and requires liver function monitoring per the iPLEDGE prescribing information [1]. A meaningful clinical question is whether glycine exerts any protective or additive hepatic effect during this window.

Evidence from Animal and Human Studies

Glycine has demonstrated hepatoprotective properties in multiple rodent models of chemical liver injury. A study published in the American Journal of Physiology showed that dietary glycine at 5% of caloric intake reduced hepatic tumor necrosis factor-alpha release and lowered ALT levels in rats after endotoxin challenge [6]. The proposed mechanism involves occupation of glycine-gated chloride channels on Kupffer cells, reducing their inflammatory activation.

Human data are more limited. A small crossover study (N=16) in healthy volunteers found that oral glycine 5 g three times daily for 5 days did not alter standard liver function tests but did reduce postprandial glycemic excursion [7]. No human trial has specifically combined glycine with isotretinoin.

Practical Guidance for Monitoring

Patients on isotretinoin already receive baseline LFTs before starting and at each follow-up visit (typically every 4 weeks for the first 2 months, then every 1 to 3 months). Adding glycine does not create a separate monitoring requirement, though your prescribing clinician should know you are taking it so any ALT elevation can be interpreted accurately.

The HealthRX clinical team uses a three-tier supplement evaluation framework for patients on isotretinoin:

• Tier 1 (avoid): Supplements with documented hepatotoxic potential or vitamin A activity (e.g., cod liver oil, high-dose vitamin A, kava, greater than 400 IU/day additional vitamin A from any source).
• Tier 2 (caution, disclose to prescriber): Supplements that modulate liver enzymes or lipid metabolism, including fish oil above 3 g/day EPA/DHA, berberine, and milk thistle at pharmacologic doses.
• Tier 3 (generally acceptable, still disclose): Well-studied amino acids with no hepatotoxic signal at standard doses. Glycine at 3 to 5 g per day falls here for most patients without pre-existing liver disease.

Glycine and Sleep During an Isotretinoin Course

Sleep disruption is a reported adverse effect of isotretinoin, likely linked to its action on retinoid receptors expressed in the central nervous system [8]. Glycine has been studied as a sleep aid through a distinct neurochemical mechanism.

The Sleep RCT Data

A double-blind, placebo-controlled crossover trial published in Sleep and Biological Rhythms (N=11) found that 3 g of glycine taken 1 hour before bedtime significantly shortened sleep-onset latency and improved subjective sleep quality scores compared with placebo [9]. A follow-up study by the same group (N=15) using polysomnography confirmed reduced time-to-sleep and improved slow-wave sleep architecture without the morning grogginess associated with pharmaceutical sleep aids [10].

The mechanism appears to involve peripheral vasodilation (glycine activates NMDA receptors and glycine-gated channels in the hypothalamus, facilitating core body temperature drop) rather than sedative receptor agonism [10].

Does This Interaction Concern Clinicians?

No. Glycine does not potentiate central nervous system depressants and does not share a mechanism with benzodiazepines, Z-drugs, or antihistamines. Patients already prescribed low-dose doxepin, melatonin, or other sleep aids alongside isotretinoin should still mention glycine to their provider, but no additive sedation risk has been identified in the literature.

Glycine, Collagen Synthesis, and Skin During Isotretinoin

Isotretinoin suppresses sebaceous gland output dramatically, which is its primary therapeutic mechanism. Some patients worry it simultaneously impairs wound healing or dermal collagen integrity.

What the Collagen Biology Shows

Glycine makes up approximately one-third of all amino acids in collagen, repeating in the classic Gly-X-Y triplet structure [11]. Oral glycine supplementation has been evaluated for its effect on skin elasticity. A randomized controlled trial published in Nutrients (N=72) tested a collagen hydrolysate supplement containing 2.5 to 5 g of peptides (rich in glycine and proline) and found a 7.2% improvement in skin elasticity at 8 weeks compared with placebo (P<0.05) [12].

Whether isolated glycine produces the same effect as collagen-hydrolysate peptides is not yet established. The peptide matrix likely provides additional signaling beyond free glycine alone.

Isotretinoin's Known Effect on Wound Healing

Isotretinoin does impair wound healing transiently. The American Academy of Dermatology recommends waiting at least 6 months after completing isotretinoin before elective procedures such as laser resurfacing or dermabrasion [13]. Glycine supplementation during the course is not a validated mitigation strategy for this concern, though its role in collagen precursor availability is biologically plausible.

Glycine and Glucose: A Consideration on Isotretinoin

Isotretinoin has been associated with hypertriglyceridemia in up to 44% of patients in some series, and less commonly with glucose dysregulation [14]. Glycine may modestly affect glycemic control through mechanisms that are not yet fully characterized.

Clinical Evidence on Glycemic Effects

A randomized crossover trial published in PLOS ONE (N=14, patients with type 2 diabetes) found that 5 g of glycine taken with a standard meal reduced postprandial glucose area-under-the-curve by approximately 16% compared with control [15]. The proposed mechanism involves glycine's ability to stimulate glucagon-like peptide-1 secretion from intestinal L-cells [16].

For the majority of isotretinoin patients, who are healthy adolescents and young adults without diabetes, this modest glucose-lowering effect is unlikely to be clinically significant. Patients with insulin resistance or pre-diabetes should mention glycine use to their clinician so the context can inform interpretation of any lab changes.

Triglyceride Considerations

Isotretinoin's hypertriglyceridemic effect is well-documented and dose-dependent [14]. Glycine does not appear to raise triglycerides. In fact, glycine is a constituent of bile acid conjugation (forming glycocholate and glycochenodeoxycholate), which facilitates lipid absorption. No evidence suggests glycine meaningfully elevates triglycerides in humans at standard supplemental doses.

Drug Interactions: What the Databases Say

The Natural Medicines Database (formerly Natural Standard) rates the evidence for a glycine-isotretinoin interaction as "insufficient," meaning no controlled studies have examined the combination directly [3]. The database does not assign a contraindication or even a moderate-concern flag for this pairing.

The FDA's drug interaction guidance for isotretinoin specifically flags vitamin A (additive toxicity), tetracyclines (pseudotumor cerebri risk), and progestin-only oral contraceptives (possible reduced efficacy), but does not list any amino acid supplements as concerns [1].

What the Prescribing Information Actually States

The isotretinoin prescribing information states: "Patients should be instructed not to take vitamin A supplements in doses greater than the recommended daily allowance" [1]. Glycine is not a vitamin, does not carry vitamin A activity, and is not mentioned anywhere in the iPLEDGE prescribing documentation.

Practical Dosing and Timing Guidance

For patients who wish to take glycine during an isotretinoin course, the following approach is consistent with the available evidence and general principles of supplement safety.

Dose Selection

3 g per day is the dose with the strongest clinical trial support for sleep-related outcomes [9][10]. Doses up to 9 g per day have been used safely in published trials without significant adverse effects in healthy adults [3]. Starting at 3 g and assessing tolerance before increasing is a reasonable approach.

Timing

Taking glycine 30 to 60 minutes before bed accomplishes two goals. First, it aligns with the timing used in the sleep-quality RCTs [9]. Second, it separates the supplement from isotretinoin, which is typically taken twice daily with meals (morning and evening) to maximize absorption via dietary fat co-ingestion [2]. A separation window of 2 to 3 hours between the evening isotretinoin dose and the glycine bedtime dose is simple to achieve.

What to Tell Your Prescriber

Disclosing all supplements to your iPLEDGE-enrolled prescriber is a basic expectation of the program. Mentioning glycine specifically allows the clinician to document it and factor it into any lab interpretation. Framing the conversation around your goals (sleep support, collagen, or general health) helps your provider give the most relevant advice.

Who Should Be More Cautious

Most isotretinoin patients are candidates for glycine supplementation without heightened concern. A few groups warrant closer clinician oversight before starting:

• Patients with baseline liver enzyme elevation before starting isotretinoin.
• Patients with a personal or family history of nonalcoholic fatty liver disease.
• Patients simultaneously taking other supplements with hepatic effects (e.g., high-dose niacin, concentrated green tea extract, or acetaminophen taken regularly for joint pain from the drug).
• Patients with insulin-treated diabetes, where even modest glycemic effects from glycine could interact with glucose management targets.

In each of these cases, the issue is not glycine alone but the cumulative context of multiple agents affecting the same organ system.

Summary of the Interaction Profile

Glycine and isotretinoin do not share a pharmacokinetic interaction pathway. The pharmacodynamic overlap is limited to three areas: liver enzyme activity (where glycine may be mildly protective rather than harmful based on animal data), glucose metabolism (where glycine may modestly lower postprandial glucose), and collagen synthesis (where glycine provides structural substrate but is not a validated replacement for the wound-healing caution associated with isotretinoin). At 3 g taken at bedtime, glycine is considered Tier 3 by the HealthRX clinical framework for most isotretinoin patients. Fasting lipid panels and LFTs required under iPLEDGE monitoring remain the appropriate safety net. Inform your prescriber before adding any supplement to your Accutane regimen.