Sleep is one of the few areas where a supplement category and a well-studied physiological system overlap closely, which makes it a useful place to see how grading works. Two products marketed side by side on the same shelf, for the same purpose, can sit three grades apart, because the grade follows the published human evidence for that specific use rather than the marketing category.
Two features of the grading system show up clearly here. Grades attach to a use, not to a molecule: a compound can carry one grade for sleep and a different grade for something else, and glycine below is an example. And a grade is capped by the kind of outcome the trials measured. Self-reported sleep quality is a legitimate endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score., but it is not polysomnography, and under the EBL rubric a self-report endpoint cannot reach Grade A no matter how well the trial was run.
Every grade below links to its own page, where the trials, the PMIDs PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed., and the reasons for the ceiling are set out in full.