Prompted by Florin Clapa, I have noted two studies1,2 finding that glucosamine supplementation raises intraocular pressure (IOP), the main driver of glaucoma. These are both very small, preliminary studies, and the more rigorously-designed1 finds a much smaller rise if any — and that apparent rise is against a lower baseline (reversion to the mean?) and seems to only emerge in a post hoc analysis of a subgroup of older patients; moreover, "Although mean rise of IOP was statistically significant in the glucosamine group, more than 2 mm Hg rise in IOP was also more in the treatment group (34% of those receiving treatment vs 12.5% of patients on placebo)." And it was done in Iran.
However, even a suggestion of a risk may not be worth it to some people, especially if their inflammation is already low or they have reason to think they're at risk of glaucoma.
References
1: Esfandiari H, Pakravan M, Zakeri Z, Ziaie S, Pakravan P, Ownagh V. Effect of glucosamine on intraocular pressure: a randomized clinical trial. Eye (Lond). 2017 Mar;31(3):389-394. doi: 10.1038/eye.2016.221. Epub 2016 Oct 21. PubMed PMID: 27768119; PubMed Central PMCID: PMC5350357.
2: Murphy RK, Ketzler L, Rice RD, Johnson SM, Doss MS, Jaccoma EH. Oral glucosamine supplements as a possible ocular hypertensive agent. JAMA Ophthalmol. 2013 Jul;131(7):955-7. doi: 10.1001/jamaophthalmol.2013.227. PubMed PMID: 23702812.
