Potkin SG, Jin Y, Bunney BG, Costa J, Gulasekaram B. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. Am J Psychiatry 1999;156:145-7.. View abstract.

Rose ML, Cattley RC, Dunn C, et al. Dietary glycine prevents the development of liver tumors caused by the peroxisome proliferator WY-14,643. Carcinogenesis 1999;20:2075-81.. View abstract. Its acid–base properties are most important. In aqueous solution, glycine is amphoteric: below pH = 2.4, it converts to the ammonium cation called glycinium. Above about 9.6, it converts to glycinate. Therefore, people with type 2 diabetes may benefit from supplementing with glycine, though research is too preliminary to make any specific recommendations.Glycine functions as a bidentate ligand for many metal ions, forming amino acid complexes. A typical complex is Cu(glycinate) 2, i.e. Cu(H 2NCH 2CO 2) 2, which exists both in cis and trans isomers.

It’s one of 20 amino acids used to make protein in the body, which builds the tissue that forms organs, joints and muscles. Of the proteins in the body, it’s concentrated in collage n (the most abundant protein in humans and many mammals) and also gelatin (a substance made from collagen). Snyder LE, Lovas FJ, Hollis JM, etal. (2005). "A rigorous attempt to verify interstellar glycine". Astrophys J. 619 (2): 914–930. arXiv: astro-ph/0410335. Bibcode: 2005ApJ...619..914S. doi: 10.1086/426677. S2CID 16286204.

Conclusion

Inagawa K, Hiraoka T, Kohda T, Yamadera W, Takahashi M. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms. 2006; 4:75-77. A study in rats found no deaths nor evidence of toxicity when feeding at the maximum protocol for toxicology studies of 2 g/kg body weight per day for 4 weeks. The LD50 dose for rats is quoted as being close to 8g/kg/day [ Shibui et al, 2013] Taking into account the fact that large animals have slower metabolisms and therefore lower tolerance than small animals, and to include a safety margin, Anroop & Jacob recommend calculating a human equivalent by dividing rat doses by 6.2. This suggests the following reasonable upper safe dose and reasonable lower toxic dose. Daily intake Szpak, Paul (2011). "Fish bone chemistry and ultrastructure: implications for taphonomy and stable isotope analysis". Journal of Archaeological Science. 38 (12): 3358–3372. doi: 10.1016/j.jas.2011.07.022.