I've used glycine in the past. Carlson has a jar of loose powder that you measure out with a small scoop. It's okay stuff but not a miracle cure by any means. It made me tired but didn't help my sleep much. I neither hated nor loved it. (Conversely melatonin makes me feel sick and groggy. I hate that stuff.)
One possibly good thing about glycine is that it's available in combination with magnesium, which definitely helps with anxiety and sleep (at least for me). You can try magnesium glycinate as a pill and see how it helps you. Personally I love magnesium and find it is a great "relaxer". Plus it's all natural, not addictive and cheap. I will mention that I'm not a huge fan of magnesium glycinate personally because it tends to constipate me. Magnesium by itself is a natural laxative in high doses but when it's combined with glycine, an amino acid, it has the opposite affect for me. So I prefer to use other types of magnesium supplementation these days. Some people love the stuff though so I guess it's personal preference.
If your goal is to calm anxiety via natural supplementation I would suggest you explore magnesium in more detail. It is available in countless varieties (oxide, citrate, glycinate, taurate, aspartate, chloride, etc.). It's also fairly cheap. Lately I've been using magnesium oxide and have been sleeping like a rock, plus I'm very calm during the day. Handling my tinnitus is much easier when I'm calm.
Good luck