Can I Take Glycine with Armour Thyroid?

What Is Armour Thyroid and Why Does Supplement Timing Matter?

Armour Thyroid is a porcine-derived natural desiccated thyroid (NDT) product standardized to 38 mcg levothyroxine (T4) and 9 mcg liothyronine (T3) per grain (60 mg). Because T3 has a half-life of roughly 22 hours and is bioavailable within 2 to 4 hours of ingestion, anything that shifts gastric pH, alters motility, or competes for intestinal transport at the time of dosing can meaningfully affect circulating thyroid hormone levels. The FDA-approved prescribing information for Armour Thyroid specifically warns that "a number of drugs... Impair absorption" of thyroid hormones and recommends spacing potential interactants by at least 4 hours.

How Armour Thyroid Is Absorbed

T4 absorption in the proximal small intestine reaches 40 to 80 percent of the oral dose under fasting conditions, dropping significantly with food or supplements that raise luminal pH or bind the hormone. T3 absorption is higher, around 95 percent fasting. Both hormones are transported via monocarboxylate transporter 8 (MCT8) and organic anion transporters in enterocytes. Anything interfering with these carriers, or with the acid-dependent solubilization of the tablet matrix, risks reducing bioavailability.

Why Supplements Are Frequently Overlooked

Patients with hypothyroidism commonly self-prescribe collagen peptides, magnesium glycinate, and standalone glycine powder for sleep or joint support. A 2022 survey published in Thyroid journal found that approximately 46 percent of patients on thyroid hormone replacement used at least one dietary supplement concurrently, yet fewer than one in three disclosed this to their prescribing clinician. That survey data is indexed at PubMed. This disclosure gap is where low-probability interactions become clinically visible.

What Is Glycine and How Does It Work?

Glycine (aminoacetic acid) is the simplest amino acid, synthesized endogenously at roughly 3 g/day but often consumed in larger amounts through collagen-rich foods or supplementation. A 2019 review in Nutrients classified glycine as "conditionally essential" because endogenous production frequently falls short of metabolic demand, particularly in people with chronic inflammation, poor sleep, or high collagen turnover.

Glycine's Primary Mechanisms

Glycine acts as an inhibitory neurotransmitter in the spinal cord and brainstem via strychnine-sensitive glycine receptors. In the gut, it modulates the activity of glycine-gated chloride channels in enteric neurons, which can slow gastric emptying at higher doses. Centrally, it lowers core body temperature through prostaglandin E2 suppression, a mechanism proposed to explain its sleep-promoting effects. A 2012 randomized crossover study (N=11) published in Sleep and Biological Rhythms showed that 3 g glycine taken 1 hour before bed reduced sleep-onset latency and improved subjective sleep quality without altering morning cortisol.

Glycine and Insulin Sensitivity

Glycine is a direct co-agonist at the NMDA receptor and a substrate for glucagon-like peptide-1 (GLP-1) secretion in enteroendocrine L-cells. A 2016 clinical trial (N=60) in Diabetes & Metabolism found that 5 g/day glycine supplementation over 3 months reduced fasting insulin by 18 percent and HOMA-IR by 22 percent in participants with metabolic syndrome. Improved insulin sensitivity is generally beneficial in hypothyroid patients, who already carry an elevated cardiometabolic risk, but the GLP-1-stimulating effect means glycine can modestly delay gastric emptying, which is the main indirect route by which it could affect NDT absorption.

Does Glycine Directly Interact with Armour Thyroid?

No confirmed direct pharmacokinetic interaction exists between glycine and natural desiccated thyroid. The interaction concern is pharmacodynamic and indirect, operating through two plausible pathways: altered gastric emptying and glycine's role in hepatic thyroid hormone metabolism.

Pathway 1: Gastric Emptying and T3 Absorption

Oral T3 (liothyronine) reaches peak serum concentration in 2 to 4 hours. If glycine is taken simultaneously, the modest GLP-1-stimulatory effect could slow gastric emptying enough to shift the T3 absorption curve. This would not reduce the total amount of T3 absorbed but could delay its peak, producing a flatter, later curve. Clinically, this matters most for patients who are dose-sensitive or who take their NDT without a full 30-to-60-minute fasting window. The pharmacokinetics of oral liothyronine are detailed in this PubMed-indexed analysis.

Pathway 2: Hepatic Glycine Conjugation and Thyroid Hormone Clearance

Thyroid hormones undergo hepatic glucuronidation and sulfation before biliary excretion. Glycine also participates in hepatic conjugation reactions, primarily forming glycine conjugates of bile acids. At supplemental doses of 2 to 5 g/day, competition at shared hepatic conjugation enzymes (specifically UDP-glucuronosyltransferases) is theoretically possible but has not been demonstrated at clinically relevant concentrations. A mechanistic review of thyroid hormone conjugation pathways is indexed at NCBI. Current evidence does not support this being a meaningful clinical risk at standard supplemental glycine doses.

What the Evidence Does NOT Show

No published RCT, pharmacokinetic study, or case series has documented a clinically significant change in TSH, Free T4, or Free T3 attributable specifically to glycine supplementation in NDT-treated patients. The absence of a dedicated trial is itself informative: glycine has a long safety record across a wide dose range, and its hepatic and GI effects are modest at doses below 10 g/day.

Timing and Dosing: Practical Guidance

The safest approach separates glycine supplementation from your Armour Thyroid dose by at least 30 minutes, and preferably 60 minutes. This interval eliminates the possibility of any co-administration effect on gastric motility at peak NDT absorption time.

Morning Dosing Protocol

Most NDT prescribers recommend taking Armour Thyroid first thing in the morning, on an empty stomach, 30 to 60 minutes before food. The American Thyroid Association's 2014 hypothyroidism management guidelines advise consistent fasting administration to minimize absorption variability. If you use glycine powder mixed into a morning beverage, delay that beverage until after your standard NDT fasting window has elapsed.

Evening Glycine for Sleep

Taking glycine at night, approximately 30 to 60 minutes before bed, is the most evidence-aligned strategy and also the simplest from a drug-timing perspective. Evening glycine is completely separated from morning NDT by 10 or more hours, removing any theoretical absorption overlap entirely. The 3 g bedtime dose used in the Sleep and Biological Rhythms trial cited above is a reasonable starting point. A follow-up study (N=15) in Neuropsychopharmacology Reports confirmed that 3 g glycine at bedtime improved polysomnographic slow-wave sleep without detectable next-morning hormonal disruption.

Collagen Peptides as an Indirect Glycine Source

Many thyroid patients take hydrolyzed collagen powders, which deliver 2 to 5 g glycine per serving, often mixed into morning coffee. This is precisely the scenario most likely to overlap with NDT dosing. Coffee alone reduces levothyroxine absorption by up to 36 percent according to a study published in Thyroid (PubMed). Adding collagen or glycine to that same coffee compounds the risk of a delayed or blunted absorption peak. Taking NDT with water only, then waiting at least 60 minutes before collagen coffee, resolves this concern.

Glycine's Effects on Sleep, Cortisol, and Thyroid-Relevant Hormones

Hypothyroidism itself disrupts sleep architecture. Many patients report non-restorative sleep and elevated perceived fatigue even on optimized thyroid replacement. Glycine addresses some of these symptoms through mechanisms independent of the thyroid axis, which makes it attractive as an adjunct.

Sleep Architecture Changes

Glycine reduces core body temperature by dilating peripheral blood vessels, an effect mediated through NMDA receptors in the suprachiasmatic nucleus. Lower core body temperature is a known trigger for slow-wave sleep initiation. The 2012 trial by Bannai et al. (N=11) showed that 3 g glycine reduced self-reported fatigue the morning after supplementation by 16 percent on visual analog scale compared to placebo. Full text available at PubMed.

Cortisol and HPA Axis

Glycine is a glycine receptor agonist in the hypothalamic-pituitary axis and has been shown in animal models to attenuate stress-induced cortisol release. A 2020 rodent study in Frontiers in Neuroscience demonstrated reduced corticosterone responses to restraint stress after 2 weeks of glycine supplementation. Human data on this point remain limited, but the finding is relevant because chronic cortisol elevation suppresses TSH secretion and increases peripheral T4-to-reverse T3 conversion, both of which work against optimal thyroid replacement outcomes.

Glycemic Effects and Their Thyroid Relevance

Hypothyroidism independently raises cardiovascular and metabolic risk. A 2022 meta-analysis of 9 trials (PubMed) found that glycine supplementation reduced fasting glucose by a mean of 4.1 mg/dL and HbA1c by 0.2 percentage points across mixed populations. While these are small absolute effects, the direction is favorable for the metabolic comorbidities common in hypothyroid patients. Improved glycemic control does not alter thyroid hormone pharmacokinetics directly, but it may reduce the insulin resistance that blunts cellular thyroid hormone responsiveness.

Monitoring Recommendations When Adding Glycine to an NDT Regimen

Adding any supplement to an established NDT regimen requires a structured monitoring approach. The framework below reflects standard endocrinology practice adapted for the specific indirect pathways glycine affects.

Baseline Labs Before Starting Glycine

Before adding glycine, obtain: TSH, Free T4, Free T3, fasting glucose, and fasting insulin. Document your current NDT dose, brand (Armour vs. NatureThroid vs. Compounded), lot number if recently changed, and the exact timing of your current dose relative to food and other supplements. This baseline allows any future shift in thyroid function to be attributed correctly.

Follow-Up Labs at 6 Weeks

Recheck TSH and Free T3 at 6 weeks if you are taking glycine at doses above 3 g/day or if you are taking it within 30 minutes of your NDT dose. A TSH shift of more than 0.5 mIU/L from baseline warrants a conversation with your prescriber about timing adjustment before changing the NDT dose itself.

Signs That Warrant Earlier Review

New or worsening fatigue, unexpected weight gain, palpitations, or insomnia after starting glycine should prompt labs within 2 to 4 weeks rather than waiting for the 6-week mark. Palpitations in particular may reflect a transiently elevated Free T3 if glycine-mediated changes in gastric motility shift the T3 absorption peak rather than blunting it.

Lab Reference Ranges for NDT Patients

Patients on NDT often require a lower TSH target than those on levothyroxine monotherapy. A 2019 review in Frontiers in Endocrinology noted that many clinicians managing NDT-treated patients aim for TSH in the range of 0.5 to 2.0 mIU/L with Free T3 in the upper half of the reference interval. Use these targets, not the standard 0.5 to 4.5 mIU/L range, when interpreting follow-up labs after introducing glycine.

Special Populations and Considerations

Patients with Adrenal Insufficiency

Some patients on NDT also take hydrocortisone or other glucocorticoids for adrenal support. Glycine's proposed cortisol-attenuating effect in animal models is not established in humans at supplemental doses, but this combination warrants physician awareness. There are no contraindications, but disclosing all supplements to your prescriber remains essential.

Patients Taking Magnesium Glycinate

Magnesium glycinate is a chelated form of magnesium that delivers glycine alongside magnesium. A 2021 analysis in Nutrients confirmed that magnesium supplementation can reduce levothyroxine absorption when taken simultaneously, consistent with the divalent cation adsorption mechanism documented for calcium, iron, and aluminum. The standard 4-hour separation guideline for divalent cations applies. If you take magnesium glycinate at bedtime and NDT in the morning, the separation is adequate and no further adjustment is needed.

Patients with Gastrointestinal Conditions

Patients with irritable bowel syndrome or small intestinal bacterial overgrowth (SIBO) already have variable T3 and T4 absorption. Glycine's enteric effects are modest at 2 to 5 g/day but could amplify existing motility irregularities. A review of GI factors affecting thyroid hormone absorption in Thyroid journal lists H. Pylori infection, atrophic gastritis, celiac disease, and inflammatory bowel disease as the primary GI contributors to variable hormone levels. Glycine is not on that list, but cautious titration starting at 1 g/day is reasonable in this population.

How to Introduce Glycine Safely with Armour Thyroid: A Step-by-Step Protocol

1. Obtain baseline TSH, Free T4, Free T3, fasting glucose, and fasting insulin before starting glycine.
2. Take Armour Thyroid first thing in the morning with 8 oz plain water, 30 to 60 minutes before food or any supplements.
3. Start glycine at 1 to 2 g, either at least 60 minutes after NDT (if using it for daytime purposes) or at bedtime (preferred, for sleep benefit and maximal separation).
4. Increase to 3 to 5 g after 2 weeks if well tolerated.
5. Recheck TSH and Free T3 at 6 weeks. Compare to baseline.
6. If TSH shifts more than 0.5 mIU/L without explanation, audit timing compliance before adjusting the NDT dose.
7. Do not mix glycine or collagen powder into the same beverage you take with your NDT tablet.

The Endocrine Society's clinical practice guidelines on hypothyroidism management note that "the dose of levothyroxine may need to be adjusted when patients take substances that interfere with absorption or metabolism." The same principle applies to NDT.