Glycine Supplements: Sleep, Blood Sugar and What the Trials Show

Glycine is the smallest amino acid. Your body makes it, and protein foods supply more; gelatin is about 30% glycine (Gannon 2002). Here we cover adults who take it by mouth: the sleep studies, blood sugar, the high-dose schizophrenia trials, GlyNAC, and who should be careful.

The short version

• Sleep (3 g at bedtime, against placebo): in one tiny trial of 7 healthy men after short nights, run by researchers at a company that makes glycine, tiredness was lower than on placebo after the first night but not by the third; a 2026 review found two other small glycine sleep trials, which also reported a benefit on at least one sleep measure. C Grade C (Bannai 2012; Fan 2026).
• Blood sugar in type 2 diabetes (against placebo): HbA1c, a 3-month sugar average, ended lower than on placebo in one 3-month trial of 74 adults. C Grade C (Cruz 2008).
• Schizophrenia, very high doses added to antipsychotics other than clozapine: small oral trials, mixed results. Small crossover trials, mostly from one research group, reported fewer negative symptoms on glycine, and a 2011 pool of glycine trials found better total and positive symptoms than placebo, but the largest trial (157 people) found no benefit. C Grade C, mixed (Heresco-Levy 2004; Singh 2011; Buchanan 2007).
• With clozapine: no benefit, and in one pooled analysis positive symptoms such as hallucinations got worse. C Grade C for harm (Singh 2011; Potkin 1999).
• GlyNAC (glycine plus NAC, a blend): lab markers improved from baseline on GlyNAC, and not on placebo, in one small trial in older adults; a larger 2-week trial found no rise in glutathione against placebo. C Grade C, mixed (Kumar 2023; Lizzo 2022).

Does glycine help you sleep?

C Grade C: small studies, several from one research group. In a randomized, single-blind crossover study, 10 healthy men who worked at a company that makes glycine slept 25% less than usual for three nights; 7 were analyzed. With 3 g of glycine before bed, they reported less fatigue than on placebo after the first short night (not by the third), a trend toward less sleepiness, and were faster on one of four computer tests (a vigilance reaction-time test) than on placebo (Bannai 2012). The same team's review describes better sleep quality, by people's own ratings, in those with insomnia tendencies (Bannai 2012 review). A 2026 scoping review found only 3 trials of glycine and sleep; each reported a benefit on at least one sleep measure (Fan 2026). The trials gave it before bedtime. The sleep supplements compared guide gives the same grade and sets glycine beside melatonin and magnesium; see also sleep health.

Does glycine lower blood sugar or help type 2 diabetes?

C Grade C: one 3-month trial found a lower HbA1c. In 74 adults with type 2 diabetes (average HbA1c 8%), 5 g of glycine a day, taken in three doses, for 3 months left HbA1c lower than on placebo (Cruz 2008). In 9 healthy adults, glycine taken with 25 g of glucose cut the rise in blood sugar by more than half, in a single-dose test (Gannon 2002). So glycine does not raise blood sugar in these studies; if anything it lowered it, which matters if you take diabetes medicine (see Safety). It does not replace diabetes medicine, diet or exercise; see type 2 diabetes and the blood sugar guide.

Does glycine lower blood pressure?

D Grade D: a drop seen only in the men of one trial. In 60 adults with metabolic syndrome (a cluster of high blood pressure, blood sugar, blood fats and waist size), 15 g a day for 3 months lowered a marker of oxidative stress by 25% against placebo, and systolic blood pressure fell significantly in the men taking glycine; the trial was designed to measure oxidative stress, and the blood pressure drop was reported for the men only (Díaz-Flores 2013). In 20 urology patients, blood pressure was lower after 3 g twice a day than before it, but that was a before-and-after comparison: the study was not randomized and placebo always came first (Sugaya 2021). See high blood pressure and the blood pressure guide.

Does glycine help inflammation or weight loss?

C Grade C for one inflammation marker; grade D for weight. In the 74-person diabetes trial, glycine also lowered TNF receptor I, a marker of inflammation, against placebo (Cruz 2008). In 19 adults with severe obesity, 2 weeks of glycine left body weight unchanged, though blood fats and liver enzymes fell from baseline; the study had no comparison group (Tan 2025). See the inflammation guide.

Does glycine help schizophrenia?

C Grade C, mixed, and only as an add-on under a psychiatrist. These trials used very large amounts, 30 to 60 g a day or up to 0.8 g per kilogram of body weight, always added to antipsychotic medicine:

• Pooled trials: a Cochrane review pooling glycine and D-serine found a moderate drop in negative symptoms (for example, low drive and flat emotion) in 132 people, but responder rates were inconsistent, neither positive symptoms nor thinking got better, and it did not separate out people on clozapine (Tuominen 2006). A 2011 meta-analysis that kept glycine apart found that, added to antipsychotics other than clozapine, it improved total and positive symptoms more than placebo, but its authors named D-serine, NAC and sarcosine, not glycine, as the add-ons with a benefit, given how few and small the trials were (Singh 2011). A 2021 review ranked glycine among the better add-ons, and found this group of add-ons worked only with antipsychotics other than clozapine (Goh 2021). A 2026 review in treatment-resistant schizophrenia pooled 9 small trials of glycine-site drugs (4 glycine, all by one research group; the rest D-serine or D-cycloserine) and found large benefits, but at low to very low certainty (Carr 2026). These pools rest mainly on small crossover trials of glycine from one research group, and two of them mix glycine with D-serine or D-cycloserine, so the cleaner evidence is the glycine-only pool and the single glycine trials below, which point both ways.
• Single trials: in a 6-week crossover of 17 people on olanzapine or risperidone, negative symptoms fell by 23% from baseline on 0.8 g per kilogram a day (Heresco-Levy 2004). But in the largest trial, CONSIST, 157 people were assigned to glycine, D-cycloserine or a dummy treatment for 16 weeks, and glycine brought no benefit for negative symptoms or thinking (Buchanan 2007).
• With clozapine: in 19 people on clozapine, 30 g a day for 12 weeks did not reduce symptoms, while positive symptoms fell by 35% from baseline in the placebo group (Potkin 1999); in 30 people, 60 g a day for 8 weeks changed nothing, and no one got clearly worse (Evins 2000); and pooled trials found glycine with clozapine worsened positive symptoms (Singh 2011).

Never stop or lower an antipsychotic, and add glycine only if your psychiatrist agrees. Our schizophrenia page gives the same grade C, mixed; see also the schizophrenia protocol and does NAC help schizophrenia?

What is GlyNAC, and does it work?

C Grade C, mixed, and it is a blend, so it can't show what glycine does alone. GlyNAC is glycine plus N-acetylcysteine (NAC), both building blocks of glutathione, an antioxidant inside cells. In 24 older adults randomized to 16 weeks of GlyNAC or an alanine placebo, low glutathione, oxidative stress, inflammation, insulin resistance and walking and strength measures improved from baseline on GlyNAC, and not on placebo (Kumar 2023). In 114 healthy older adults, 2.4 to 7.2 g a day for 2 weeks did not raise glutathione against placebo; in a later look, glutathione rose from baseline only in a subgroup with high oxidative stress and low glutathione, a within-group change rather than a comparison with placebo. Most authors of that trial work for a food company that holds patents and licenses for glycine and NAC products, as its conflict-of-interest statement says (Lizzo 2022). The NAC guide covers NAC on its own.

Does glycine help anxiety or OCD?

No trial has tested glycine supplements for anxiety in people; the nearest is one small OCD trial. For obsessive-compulsive disorder (OCD), 24 adults on steady treatment were randomized to add glycine, built up to 60 g a day, or a placebo; only 14 could be assessed, mostly because people quit over the taste or nausea, and the drop in symptoms against placebo just missed statistical significance (Greenberg 2009). That is grade C at best. See the OCD guide.

Is collagen or gelatin a good source of glycine?

Gelatin is about 30% glycine (Gannon 2002), and collagen is rich in it. A 2026 scoping review found that glycine and collagen supplements raised blood glycine in absorption studies; for sleep, one placebo-controlled collagen trial found fewer night awakenings and another lower fatigue, while collagen did no better than alpha-lactalbumin, a milk protein, in comparison studies (Fan 2026). Whether collagen's glycine is what helps has not been tested. See the collagen guide.

What we'd skip

• Glycine in place of antipsychotic medicine, or with clozapine without your psychiatrist: it was only ever tested as an add-on, and with clozapine it gave no benefit or worse positive symptoms (Singh 2011; Potkin 1999).
• Glycine for weight loss: weight did not change in a small 2-week study (Tan 2025).
• GlyNAC to raise glutathione in healthy older adults: the larger trial found no rise against placebo (Lizzo 2022).

Safety and interactions

• Stomach upset and taste: at the very high amounts in psychiatric trials, taste complaints and nausea made many people stop (Greenberg 2009). At 3 g twice a day for 4 weeks, the urology study recorded no adverse events (Sugaya 2021), and none of 19 adults with severe obesity had side effects over 2 weeks (Tan 2025).
• GlyNAC and heart medicines: GlyNAC contains NAC. In a 200-person trial in unstable angina, 35% of those given oral NAC with a nitroglycerin patch had side effects, mostly intolerable headache, which was almost twice as common as on the patch alone (Ardissino 1997); NAC and nitroglycerin given into a vein caused symptomatic low blood pressure in 7 of 24 people, against none on nitroglycerin alone (Horowitz 1988). If you use nitroglycerin or another nitrate, ask your prescriber before taking GlyNAC.
• Clozapine: don't add glycine to clozapine on your own; in trials it brought no gain, and pooled data showed worse positive symptoms (Singh 2011). Tell your psychiatrist about any supplement.
• Diabetes medicines (metformin, insulin and others): glycine lowered HbA1c in one trial and blunted the sugar rise after glucose (Cruz 2008; Gannon 2002). No studies have tested it with specific diabetes medicines; test your blood sugar more often after starting it and tell your prescriber.
• Blood pressure medicines: systolic pressure fell in the men taking glycine in one trial (Díaz-Flores 2013). No studies have tested glycine with blood pressure medicines; watch for dizziness on standing.
• Sertraline, trazodone, melatonin, magnesium or apixaban (Eliquis): no studies have tested glycine with any of them. Ask your pharmacist, and avoid stacking several products sold for sleep.
• Kidney or liver disease: glycine supplements have not been studied in people with these conditions; ask your doctor first.
• Upper limit: there is no set upper limit for glycine. Sleep studies used 3 g; diabetes and blood pressure trials 5 to 15 g a day; psychiatric trials up to 60 g a day under supervision (Bannai 2012; Cruz 2008; Díaz-Flores 2013; Evins 2000). Check your stack if you combine products.
• Pregnancy: no human studies of glycine supplements in pregnancy exist; use glycine only on the advice of your midwife or obstetric team.
• Breastfeeding? Ask your midwife, doctor or a lactation specialist, who can check what passes into breast milk.
• Children: talk to your child's doctor first.

When to see a doctor

• Sleep: weeks of poor sleep, loud snoring, gasping at night or dozing off in the daytime can point to sleep apnea or other conditions a doctor can treat; get checked before relying on a supplement. See obstructive sleep apnea.
• Same day for new or worse hallucinations, paranoia or confusion, especially if you take an antipsychotic.
• Low blood sugar on diabetes medicine: shaking, sweating or confusion; treat it and call your care team.
• Suicidal thoughts: in the US, call or text 988 now.

Don't stop a prescribed medicine on your own; ask the prescriber or pharmacist. If pregnant, let your midwife or obstetric team guide you; anyone under 18 should ask a clinician first.

FAQ

Does glycine help you sleep? A little, in one tiny study (grade C): in 7 healthy men whose sleep was cut short, 3 g at bedtime meant less tiredness than placebo after the first short night, though not by the third. That study was run by researchers at a company that makes glycine.

When and how much glycine did sleep studies use? 3 g, taken before bedtime. There is no set upper limit for glycine.

Does glycine raise blood sugar? Not in the studies: in 74 adults with type 2 diabetes, HbA1c ended lower than on placebo after 3 months (grade C), and in 9 healthy adults it blunted the rise after glucose. On diabetes medicine, test your blood sugar more often after starting it.

Can I take glycine with sertraline, trazodone or melatonin? No studies have tested glycine with these medicines or with melatonin. Ask your pharmacist, and avoid stacking several sleep products.

Is glycine safe to take every day? Small trials gave 3 to 15 g a day for up to 3 months; two that tracked side effects, at 6 g a day and at about 100 mg per kilogram a day, found none, while very high psychiatric doses caused nausea. Studies have not covered pregnancy, breastfeeding, or kidney or liver disease, and it should not be added to clozapine without your psychiatrist.

Related pages

• Glycine · Collagen · N-acetylcysteine (NAC) · Glutathione
• Sleep health · Sleep health protocol · Insomnia · Schizophrenia · Schizophrenia protocol · Type 2 diabetes · Metabolic syndrome
• Sleep supplements compared · NAC · Collagen · Blood sugar · Blood pressure · OCD
• Check my stack · How we grade

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