Can I Take Glycine with Amlodipine?

What Is Glycine and Why Do People Take It with a Blood Pressure Drug?

Glycine is the smallest amino acid. The body produces it endogenously, and dietary sources include collagen-rich foods such as bone broth and skin-on poultry. Supplemental glycine is sold primarily for sleep quality, skin collagen support, and blood-sugar management, at doses ranging from 3 g to 15 g per day. Bannai et al. (2012) showed that a single 3 g dose taken 1 hour before bed cut sleep-onset latency and reduced daytime fatigue in a small crossover study (N=11), which is the origin of the popular bedtime-dosing protocol.

Amlodipine is one of the most prescribed antihypertensives in the United States. It works by blocking L-type calcium channels in vascular smooth muscle, producing arterial dilation and sustained blood-pressure reduction lasting 24 hours with a single daily dose. The 2023 ACC/AHA Hypertension Guideline lists long-acting dihydropyridine calcium-channel blockers such as amlodipine as first-line agents for most adults with hypertension.

People combine the two because collagen peptides and glycine have become mainstream wellness supplements. Patients on amlodipine for years may add glycine without thinking of it as something that requires a drug-interaction check.

Why the Combination Deserves a Closer Look

Glycine is not simply inert. It acts on glycine receptors (GlyR) expressed in vascular endothelium and smooth muscle, and animal data suggest it can reduce mean arterial pressure by 5 to 10 mmHg through a nitric-oxide-dependent pathway. A 2003 rodent study published in Cardiovascular Research found that intravenous glycine lowered portal venous pressure in rats with cirrhosis, pointing to real hemodynamic activity. The vasodilatory magnitude in humans appears smaller at oral doses, but it is not zero.

What This Means for an Amlodipine Patient

A person already achieving a systolic blood pressure of 118 mmHg on amlodipine 10 mg has little physiological buffer before symptoms of low blood pressure appear. Adding 10 to 15 g of glycine per day may tip that balance. The concern is not toxicity. The concern is additive hemodynamic effect at higher glycine doses.

Pharmacokinetics: Does Glycine Change How Amlodipine Is Absorbed or Metabolized?

No. Glycine does not meaningfully inhibit or induce CYP3A4, the hepatic enzyme responsible for metabolizing roughly 90% of an amlodipine dose. Amlodipine's prescribing information (FDA label) identifies CYP3A4 inhibitors such as clarithromycin and strong CYP3A4 inducers such as rifampin as meaningful interaction risks. Glycine belongs to neither category.

Glycine is absorbed via the small intestine through sodium-dependent neutral amino acid transporters (SLC6A9, SLC1A5). These transporters are structurally unrelated to the intestinal P-glycoprotein system that affects many cardiovascular drugs. Amlodipine's oral bioavailability of 64 to 90% is therefore unaffected by glycine co-administration.

Half-Life Considerations

Amlodipine has an unusually long plasma half-life of 35 to 50 hours, meaning steady-state plasma concentrations change slowly. Even if glycine produced a modest hemodynamic effect for 4 to 6 hours after ingestion, the additive risk window is self-limiting. This pharmacokinetic reality reduces concern about acute blood-pressure spikes substantially.

Protein Binding

Amlodipine is approximately 93% protein-bound in plasma. Glycine does not compete for albumin or alpha-1-acid glycoprotein binding sites in the same concentration range reached by oral supplementation. A displacement interaction is not a realistic concern at doses used clinically.

Pharmacodynamics: Where the Real Interaction Lives

This is where caution is warranted. Both compounds lower blood pressure through distinct but potentially additive pathways.

Amlodipine's Mechanism

Amlodipine blocks voltage-gated L-type calcium channels in arterial smooth muscle. The result is reduced intracellular calcium, smooth-muscle relaxation, and decreased peripheral vascular resistance. In the landmark ALLHAT trial (JAMA, 2002, N=33,357), chlorthalidone, amlodipine, and lisinopril were compared head-to-head; amlodipine produced mean systolic reductions of approximately 9 mmHg from a baseline of 146 mmHg at five years.

Glycine's Vascular Effects

Glycine activates inhibitory glycine receptors on vascular endothelial cells, which may stimulate nitric oxide synthase (NOS) activity and promote endothelium-dependent vasodilation. A 2000 study in Circulation demonstrated that glycine infusion protected against ischemia-reperfusion injury in cardiac tissue partly by reducing calcium overload in cardiomyocytes, an effect mechanistically adjacent to what calcium-channel blockers produce.

At oral doses of 3 g (the sleep dose), this vascular effect is minor. At 10 to 15 g per day, which some collagen-supplement protocols recommend, the cumulative vasodilatory contribution may be clinically detectable in sensitive individuals.

Blood Sugar and Insulin Secretion

Glycine stimulates glucagon-like peptide-1 (GLP-1) release from intestinal L-cells and enhances insulin secretion directly from pancreatic beta cells. A randomized crossover study by Gannon et al. Published in the American Journal of Clinical Nutrition (2002) showed that oral glycine ingestion increased insulin area-under-the-curve significantly in healthy adults. Amlodipine has a small but measurable inhibitory effect on insulin secretion through calcium-channel blockade in the pancreas. The net glycemic direction when combining the two is neutral to mildly beneficial, but patients with diabetes using insulin secretagogues should be aware.

Sleep Quality: The Most Common Reason for Combining Both

Most patients asking this question take amlodipine in the morning and glycine at bedtime. That temporal separation is worth noting because it minimizes the overlap of peak plasma concentrations.

The Evidence for Glycine as a Sleep Aid

The Bannai 2012 trial referenced above (N=11, crossover design) used 3 g glycine and found statistically significant improvement in Pittsburgh Sleep Quality Index scores. A follow-up by the same group, Bannai et al. (2012) in Neuropsychopharmacology Reports, confirmed polysomnographic reductions in sleep-onset latency. The working mechanism involves glycine's action on NMDA receptors in the suprachiasmatic nucleus, which modulates core body temperature drop at sleep onset.

Timing and Blood Pressure at Night

Amlodipine taken in the morning produces its maximal antihypertensive effect during daytime hours when sympathetic tone is highest. Nocturnal blood pressure in amlodipine-treated patients is already lower than daytime readings. Adding glycine at 9 to 10 pm in a patient whose nighttime systolic already runs 105 to 108 mmHg could occasionally cause orthostatic dizziness upon waking. Starting at 2 to 3 g rather than 5 to 10 g is the prudent approach.

Collagen Synthesis Protocols: Higher Doses and What to Watch

Some patients take glycine specifically because type I collagen synthesis requires glycine as a rate-limiting substrate. A paper in Amino Acids (2018) calculated that endogenous glycine synthesis falls short of collagen demands by approximately 10 g per day in adults, suggesting that higher supplemental doses have a physiological rationale.

10 to 15 g Per Day: Risk Profile in Amlodipine Users

At these higher doses, the vasodilatory signal from glycine receptor activation becomes more relevant. Patients on amlodipine 5 to 10 mg should:

• Check seated and standing blood pressure on days 1, 3, 7, and 14 after starting a higher-dose glycine protocol.
• Record any lightheadedness, palpitations, or flushing, which overlap symptomatically with amlodipine's known side effects (peripheral edema affects 10.8% of patients at 10 mg per the FDA label).
• Titrate glycine upward by 2 to 3 g per week rather than starting at the full target dose.

The Collagen Co-Factor Stack Question

Many collagen protocols combine glycine with vitamin C, proline, and lysine. Vitamin C at doses above 1,000 mg per day may mildly reduce amlodipine plasma concentrations by competing for intestinal absorption via shared transporters, though the clinical magnitude of this effect is modest. Lysine and proline carry no known interaction signal with calcium-channel blockers. The glycine component remains the main pharmacodynamic consideration.

Which Patients Need Extra Caution?

Not everyone taking amlodipine carries the same risk profile when adding glycine. The following groups deserve closer monitoring.

Patients on Amlodipine 10 mg

The maximum approved dose (10 mg daily) produces the greatest degree of peripheral vasodilation. Adding glycine's mild vasodilatory signal on top of a maximally dilated vascular bed leaves less room before symptomatic hypotension occurs.

Elderly Patients and Orthostatic Hypotension

The ACC/AHA 2019 guidelines on hypertension in older adults note that orthostatic hypotension affects up to 20% of adults over age 65 on antihypertensives. Glycine's vasodilatory effect, even at 3 g, could push a borderline orthostatic response into symptomatic territory in this population.

Patients Also Taking Other Vasodilators

Amlodipine is sometimes combined with ACE inhibitors, ARBs, or nitrates. Adding glycine to a triple vasodilator regimen warrants explicit discussion with the prescribing physician before starting, regardless of dose.

Patients with Type 2 Diabetes on Sulfonylureas

Because glycine potentiates insulin secretion and sulfonylureas independently lower blood glucose, the combined glycemic effect may be additive. This is a secondary concern relative to blood pressure, but worth monitoring with fasting glucose checks in the first two weeks.

Monitoring Protocol: A Practical Checklist

The following steps are appropriate for most adults who decide to start glycine while taking amlodipine, based on the pharmacodynamic considerations above and standard clinical practice for adding supplements to antihypertensive regimens.

1. Measure baseline seated and standing blood pressure on the day before starting glycine.
2. Start glycine at 2 to 3 g per night at bedtime, not at the target collagen dose.
3. Recheck seated and standing blood pressure on day 3 and day 7.
4. If systolic blood pressure drops more than 15 mmHg from baseline or falls below 100 mmHg systolic, pause glycine and contact the prescribing clinician.
5. If no symptoms and blood pressure is stable after 14 days, titrate to the target glycine dose in 2 to 3 g weekly increments.
6. Report dizziness, ankle swelling that worsens, or flushing to the prescribing clinician, as these overlap with amlodipine side effects and the combination may need reassessment.

The NIH Office of Dietary Supplements fact sheet on dietary supplement interactions categorizes glycine as generally recognized as safe (GRAS) at doses up to 31 g per day in the context of food use, but GRAS status does not account for pharmacodynamic interactions with antihypertensives.

What Clinicians Say About Amino Acid Supplements in Hypertensive Patients

The American Heart Association's scientific statement on dietary approaches to prevent and treat hypertension, published in Hypertension (2021), states: "Dietary protein, particularly from plant sources, is associated with lower blood pressure, with each 25-g/day increment in total protein intake associated with a 1.76 mmHg lower systolic blood pressure." Glycine is a primary amino acid in plant protein concentrates and collagen, and this statement implies that modest blood-pressure-lowering from amino acid supplementation is a real, if small, physiological effect.

A 2021 meta-analysis in Nutrients (PMID 34684425) examining collagen peptide supplementation (which contains high glycine fractions) across 15 RCTs found no serious adverse cardiovascular events, though none of the trials specifically enrolled patients on calcium-channel blockers. The absence of reported harm is reassuring but not the same as a controlled interaction study.

Practical Dosing Summary

For the average adult taking amlodipine 5 mg or 10 mg once daily in the morning who wants to add glycine for sleep or collagen synthesis:

• Sleep goal (3 g at bedtime): Low risk. Temporal separation from the morning amlodipine dose reduces pharmacodynamic overlap. Monitor blood pressure for two weeks.
• Collagen synthesis goal (10 to 15 g split across meals): Moderate caution. Titrate slowly, monitor blood pressure and orthostatic symptoms at each dose increment.
• Avoid starting high-dose glycine (above 10 g per day) without telling your prescriber, particularly if you are also on a nitrate, another antihypertensive, or a sulfonylurea.

No dose-separation interval is required from a pharmacokinetic standpoint, because the interaction is pharmacodynamic rather than metabolic. Separating the doses by several hours may still reduce symptom overlap during the highest plasma-concentration period of each compound.