Can I Take Glycine With Avodart (Dutasteride)?

Is There a Known Interaction Between Glycine and Dutasteride?

The Avodart label's drug interactions section does not list glycine [1]. We found no published human study that tested glycine with dutasteride.

The label discusses potent, chronic CYP3A4 inhibitors such as ritonavir. It separately covers alpha-adrenergic antagonists, calcium channel antagonists, cholestyramine, digoxin and warfarin [1]. Dutasteride is extensively metabolized by CYP3A4 and CYP3A5, and the label says the effect of potent CYP3A4 inhibitors on dutasteride has not been studied [1].

Glycine is a non-essential amino acid sold over the counter as a dietary supplement [2][3]. Doses in human studies include 3 g before bedtime in a sleep-restriction trial and 30 g/day or 60 g/day in trials added to clozapine [4][5][6]. These are study doses, not recommended doses. The only drug-related signal found for glycine involves clozapine, not dutasteride. In a 19-patient trial, glycine 30 g/day added to clozapine did not reduce symptoms, while the clozapine-alone group had a 35% fall in positive symptoms; the authors suggested glycine might interfere with clozapine [5]. A separate 30-patient trial at 60 g/day found no significant change in symptoms or cognition and no clinically significant worsening [6]. Both used doses 10 to 20 times the 3 g used in the sleep trial.

What the Avodart Label Covers

Avodart is dutasteride 0.5 mg soft gelatin capsules for symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate; hair-loss use is off-label [1]. The label says to swallow the capsule whole and not chew or open it, and says it may be taken with or without food [1].

Common adverse reactions in pooled 2-year BPH trials during months 0 to 6 were impotence 4.7% with dutasteride vs 1.7% with placebo, decreased libido 3.0% vs 1.4%, ejaculation disorders 1.4% vs 0.5%, and breast disorders 0.5% vs 0.2% [1]. The label says these sexual adverse reactions may persist after discontinuation and the role of dutasteride in that persistence is unknown [1].

The label also says dutasteride lowers serum PSA by about 50% within 3 to 6 months [1]. It says a new PSA baseline should be established at least 3 months after starting, an isolated PSA in a man treated for 3 months or more should be doubled for comparison with untreated men, and any confirmed rise from the lowest on-treatment PSA should be evaluated [1].

What the Glycine Trials Show

In a 2012 trial, healthy volunteers whose sleep was cut by about 25% for three nights took 3 g of glycine or placebo before bed. Glycine reduced fatigue and improved psychomotor vigilance, and it had no significant effect on plasma melatonin [4]. This was not an insomnia treatment trial.

The higher doses have been tested in schizophrenia. The clozapine trials used 30 g/day for 12 weeks in 19 patients and 60 g/day for 8 weeks in 30 adults [5][6]. GlyNAC, a glycine plus N-acetylcysteine combination, was described as safe and well tolerated in a 24-person 16-week trial and a 114-person 2-week dose trial, but neither abstract reports a side-effect list for glycine alone [7][8].

What This Means for Taking Them Together

The label's lack of a glycine entry reflects what has been tested, not a finding of safety: no human data on the pair were found. For dutasteride itself, the label's own side-effect and PSA statements are the relevant safety facts [1].