Can I Take Glycine With Avodart (Dutasteride)?

How Dutasteride and Glycine Are Metabolized

Dutasteride and glycine travel through entirely different metabolic channels, which is the main reason a pharmacokinetic interaction is unlikely.

Dutasteride's CYP3A4 Pathway

Dutasteride (brand name Avodart) is a dual 5-alpha reductase inhibitor approved by the FDA for benign prostatic hyperplasia (BPH) at 0.5 mg daily. It undergoes extensive hepatic metabolism primarily through CYP3A4 and, to a lesser extent, CYP3A5. The drug's terminal half-life at steady state is roughly 5 weeks, meaning it accumulates slowly in tissue and is sensitive to strong CYP3A4 inhibitors such as ritonavir and ketoconazole [1]. Any supplement that meaningfully inhibits or induces CYP3A4 could, in theory, alter dutasteride exposure.

Glycine's Independent Clearance

Glycine is the simplest amino acid (molecular weight 75.03 Da). It is absorbed in the jejunum via active transport, enters the systemic amino acid pool, and is cleared through the mitochondrial glycine cleavage system in the liver and kidneys, plus conjugation reactions that produce hippuric acid [2]. Glycine does not undergo CYP-mediated oxidation and has shown no inhibitory or inductive activity on CYP3A4 in human liver microsome assays reported in the Natural Medicines Comprehensive Database. That separation in clearance pathways means glycine should not change dutasteride plasma concentrations at standard supplemental doses (3 to 15 g/day) [3].

A 2012 pharmacokinetic review of amino acid supplements confirmed that simple amino acids like glycine, taurine, and L-theanine lack clinically meaningful CYP enzyme interactions at doses up to 15 g/day in healthy adults [3].

Pharmacodynamic Considerations: Sleep, Glucose, and Collagen

Even when two substances avoid a pharmacokinetic clash, they can still interact pharmacodynamically, affecting the same physiological systems. Three areas deserve attention.

Glycine and Sleep Architecture

Glycine at 3 g before bed has been studied for its effects on sleep quality. In a randomized crossover trial (N=11), 3 g of oral glycine reduced subjective sleepiness the next day and improved sleep efficiency measured by polysomnography, likely through NMDA-receptor mediated thermoregulation in the suprachiasmatic nucleus [4]. Dutasteride itself is not sedating, but BPH-related nocturia disrupts sleep in 50 to 70% of men over 50 [5]. Adding glycine could have an additive benefit on sleep continuity in this population. No adverse pharmacodynamic interaction is expected.

Glycine and Blood Glucose

High-dose glycine (5 to 15 g/day) may lower fasting glucose by 5 to 8% according to a meta-analysis of nine trials (N=478) published in Nutrients [6]. The proposed mechanism is enhanced insulin secretion via GLP-1 stimulation in enteroendocrine L-cells. Dutasteride, through DHT reduction, has been associated with modest increases in fasting insulin and HOMA-IR in some observational cohorts, including a secondary analysis of the REDUCE trial (N=6,729), though this finding has not been consistent across studies [7].

The clinical significance is small. But for men already on the metabolic borderline (HbA1c 5.7 to 6.4%), the opposing effects on insulin sensitivity could either cancel out or create unpredictable net changes. Monitoring fasting glucose every 6 months is reasonable when combining dutasteride with glycine at doses above 5 g/day.

Glycine and Collagen Synthesis

Glycine serves as a direct substrate for collagen synthesis: roughly one-third of all amino acid residues in type I collagen are glycine. A 2019 study by Shaw et al. Found that 5 g of glycine combined with vitamin C, taken 60 minutes before exercise, doubled the rate of collagen synthesis biomarkers (PINP) compared to placebo [8]. Men using dutasteride for androgenetic alopecia (off-label) sometimes add glycine hoping to support hair follicle extracellular matrix. No data confirm that glycine accelerates or inhibits hair regrowth from 5-alpha reductase inhibition, so these remain parallel, non-interacting pathways.

What the Interaction Databases Say

Both the Natural Medicines Comprehensive Database (accessed May 2026) and the Mayo Clinic Drug Interaction Checker list no known interaction between glycine and dutasteride. The FDA label for Avodart warns about interactions with CYP3A4 inhibitors (citing verapamil, diltiazem, ritonavir, and ketoconazole) but does not mention amino acid supplements [1].

Why No Direct Trial Exists

Drug-supplement interaction trials are expensive and typically funded only when preclinical signals suggest a risk. Because glycine does not share CYP enzymes, P-glycoprotein transport, or plasma protein binding sites with dutasteride, no regulatory or academic body has prioritized a dedicated interaction study. The absence of evidence is not evidence of absence, but the pharmacological basis for concern is thin.

Guideline Positions

The American Urological Association (AUA) BPH guideline (2023 amendment) does not address amino acid supplementation during 5-alpha reductase inhibitor therapy. The Endocrine Society's position on supplements and hormonal therapy broadly recommends disclosing all supplements to prescribers but identifies no amino acid class as a concern with anti-androgen agents [9].

Dosing and Timing Recommendations

There is no pharmacological reason to separate dutasteride and glycine by a specific time window. Practical GI comfort may benefit from a short gap.

Suggested Daily Schedule

Dutasteride is taken once daily (0.5 mg) at a consistent time. Most prescribers recommend morning dosing with food. Glycine, if used for sleep, is typically taken as 3 g dissolved in water 30 to 60 minutes before bed. This natural timing gap of 12+ hours makes co-administration issues irrelevant for the majority of users.

For glycine taken as a collagen-support dose (5 g with vitamin C, pre-exercise), morning dosing alongside dutasteride is acceptable. A 2-hour separation is optional and based on general GI tolerance rather than drug interaction data.

Dose Ranges in Published Research

| Use case | Glycine dose | Frequency | Key citation | |---|---|---|---| | Sleep quality | 3 g | Once at bedtime | Inagawa et al. 2006 [4] | | Collagen synthesis | 5 g + 50 mg vitamin C | Pre-exercise | Shaw et al. 2019 [8] | | Glycemic modulation | 5 to 15 g | Divided doses with meals | Yan-Do & MacDonald 2017 [6] | | General supplementation | 1 to 3 g | Once daily | No specific trial |

Monitoring if You Take Both

Routine monitoring for dutasteride (PSA, DHT, liver function tests at baseline) does not change because of glycine co-administration. Two additions are worth considering.

Fasting Glucose Check

If glycine intake exceeds 5 g/day and the patient has prediabetes (HbA1c 5.7 to 6.4%) or is overweight (BMI >25), check fasting glucose at 3 and 6 months after starting glycine. The REDUCE trial secondary analysis found a 9% higher rate of incident type 2 diabetes in the dutasteride arm versus placebo over 4 years, though the absolute risk increase was modest (1.4% vs. 0.8%, P=0.02) [7]. Adding a glucose-lowering supplement into that picture warrants tracking.

Renal Function in Older Adults

Glycine is renally cleared. In men over 70 with eGFR <60 mL/min/1.73 m², high-dose glycine (>10 g/day) could theoretically accumulate, though this has not been reported in clinical trials. A baseline metabolic panel before starting high-dose glycine is prudent in this demographic [10].

When to Talk to Your Prescriber

Most men can add 3 g of bedtime glycine to an existing dutasteride regimen without a prescriber visit. Flag the combination at your next appointment. Seek earlier consultation if you are:

• Taking a strong CYP3A4 inhibitor (e.g., ketoconazole, ritonavir, clarithromycin) alongside dutasteride, because adding any supplement increases polypharmacy complexity.
• Using glycine at doses above 10 g/day for athletic or collagen purposes.
• Diagnosed with chronic kidney disease (stage 3 or higher).
• Experiencing new-onset hypoglycemic symptoms (dizziness, sweating, shakiness) after starting glycine.

The AUA guideline recommends maintaining a complete supplement log at every BPH follow-up visit, and glycine should appear on that list [9].

What About Other Amino Acids and Dutasteride?

Glycine is among the safest amino acids to combine with 5-alpha reductase inhibitors. Some amino acids with documented CYP interactions deserve more caution.

Amino Acids With Greater CYP3A4 Relevance

L-tryptophan competes for CYP1A2 and CYP2C9, not CYP3A4, but its serotonergic effects could theoretically interact with SSRIs that many BPH patients take concurrently. N-acetylcysteine (NAC) at very high doses (>1,800 mg/day) has shown mild CYP3A4 inhibition in vitro, though clinical significance remains unclear [11]. Glycine carries none of these liabilities.

The Broader Supplement Question

A 2021 cross-sectional analysis of NHANES data found that 52.1% of U.S. Men aged 50 to 70 take at least one dietary supplement, yet only 33% of those men inform their urologist [12]. For patients on dutasteride, disclosing every supplement, including amino acids, protein powders, and herbal extracts, allows prescribers to screen for CYP3A4 interactions that actually matter (St. John's wort as an inducer, grapefruit-derived supplements as inhibitors).

Bottom Line: Safety Profile of the Combination

The glycine-dutasteride combination carries no identified pharmacokinetic interaction and only minor, manageable pharmacodynamic overlaps in glucose metabolism. Standard dutasteride monitoring applies. Add fasting glucose surveillance if glycine exceeds 5 g/day in metabolically at-risk patients. No dose adjustment to either agent is required.