Glycine for Sleep: My Skepticism, the Science, and Why I Now Recommend It

I'll admit it—I was pretty dismissive of glycine as a sleep supplement for years. In naturopathic school, we learned about it as a non-essential amino acid, a component of collagen, something your body makes. The idea that taking a few grams before bed could meaningfully change sleep architecture felt... simplistic. Then, about five years ago, a patient with stubborn insomnia—a 52-year-old software engineer who'd tried everything from valerian to prescription sleep aids—asked me about it. I told him the evidence was probably weak, but if he wanted to try, use 3 grams. He came back two weeks later saying it was the first thing that helped him fall asleep faster and feel more rested. That made me actually look at the research. And here's what changed my mind.

Quick Facts: Glycine at a Glance

What the Research Actually Shows

So, the traditional use is interesting—glycine's been in the wellness space for a while—but the data is what convinced me. Let's look at two key areas.

1. Sleep Architecture and Quality
This is where the evidence is strongest. A really well-designed 2007 study published in Sleep (30(12):1695-1703) gave 3g of glycine or placebo to 11 healthy volunteers with sleep complaints. They used polysomnography (the gold standard for sleep measurement) and found glycine significantly shortened sleep latency—that's the time it takes to fall asleep—and improved sleep efficiency (the percentage of time in bed actually spent sleeping). Participants also reported feeling more refreshed in the morning. The mechanism here appears to be thermoregulation: glycine causes peripheral vasodilation, which lowers core body temperature by about 0.5-1.0°C. Your body needs to drop temperature to initiate sleep, and glycine gives it a nudge.

2. Metabolic Markers
Here's where it gets even more interesting. Glycine isn't just for sleep. A 2021 randomized controlled trial (PMID: 34426588) looked at 60 adults with metabolic syndrome. They were given 15g of glycine daily (5g three times a day) for 12 weeks. Compared to placebo, the glycine group saw significant improvements in fasting insulin (down 26%, p<0.01), HOMA-IR (a measure of insulin resistance, down 29%, p<0.01), and triglycerides. Now, 15g is a higher dose than the sleep dose, but it suggests glycine plays a role in glucose metabolism. For the biochemistry nerds: glycine is involved in glutathione synthesis (your master antioxidant) and may improve insulin signaling. In practice, I've seen patients on 3g at night report better fasting glucose numbers on their labs after a few months.

Point being: the sleep benefits have decent human trial support, and the metabolic effects are promising though more research is needed on lower doses.

Dosing, Timing, and What to Buy

Okay, so how do you actually use this? Here's my clinical protocol.

Dose: 3 grams (3,000 mg) before bed. That's the dose used in most sleep studies. Some studies on metabolic health use higher doses (like the 15g/day one), but for sleep, stick with 3g. You can start with 1-2g if you're sensitive, but most people tolerate 3g fine.

Timing: Take it 30-60 minutes before bedtime. That gives it time to lower your core body temperature. I usually tell patients to take it when they start their bedtime routine—brush teeth, take glycine, read a book.

Form: Powder is best. It mixes easily in water or herbal tea (it's slightly sweet). Capsules are fine if you prefer, but you'll need several to get to 3g. Avoid proprietary blends that mix glycine with other sleep ingredients unless you know the exact amounts—this drives me crazy, because you can't adjust the dose.

Brands I recommend:

• Thorne Research Glycine – my top pick. Consistently pure, no additives, NSF Certified for Sport.
• NOW Foods Glycine Powder – good value, also pure, often available in bulk.
• Jarrow Formulas Glycine – another reliable brand.

Can you get it from food? Yes, but not enough for the sleep effect. Glycine is high in collagen-rich foods: bone broth, chicken skin, gelatin. But to get 3g, you'd need about 10 cups of bone broth. So supplementation makes sense here.

Who Should Avoid or Be Cautious

Glycine is generally very safe, but a few caveats.

• Kidney disease: If you have severe kidney impairment (e.g., stage 4-5 CKD), avoid high-dose glycine without medical supervision. Amino acids are processed by the kidneys.
• Schizophrenia or bipolar disorder: There's some old research suggesting glycine might interact with certain antipsychotic medications (like clozapine). The evidence is mixed, but if you're on these, talk to your psychiatrist first.
• Pregnancy/breastfeeding: Not enough safety data, so I don't recommend it during these periods.
• Side effects: Rare, but some people report mild stomach upset at higher doses (>10g). At 3g, it's usually well-tolerated.

Frequently Asked Questions

Q: Will glycine make me groggy in the morning?
A: No, that's the interesting part. Unlike some sleep aids, glycine doesn't cause morning grogginess. In fact, studies show improved daytime alertness. It seems to improve sleep quality without sedation.

Q: Can I take glycine with melatonin?
A: Yes, they work by different mechanisms. Glycine lowers body temperature; melatonin regulates circadian rhythm. Some patients do well with both. Start with one at a time to see what works for you.

Q: How long until I see results?
A: For sleep, often within a few nights. For metabolic markers, give it 4-8 weeks. It's not an instant fix, but it's consistent.

Q: Is glycine the same as collagen?
A: No, glycine is one amino acid in collagen. Collagen supplements contain glycine (about 20-30% by weight), but you'd need a lot of collagen to get 3g of glycine. If sleep is your main goal, pure glycine is more cost-effective.

Bottom Line

• Glycine at 3g before bed can improve sleep onset and quality by lowering core body temperature—the data here is solid.
• It may also benefit metabolic markers like insulin sensitivity, though more research is needed on the sleep-dose effects.
• Use pure powder from a reputable brand (Thorne, NOW, Jarrow) and avoid proprietary blends.
• It's safe for most people, but skip it if you have severe kidney disease or are pregnant.

Disclaimer: This is for informational purposes only and not medical advice. Consult your healthcare provider before starting any new supplement.