I want to provide a counterpoint to the glowing reviews. I tried magnesium glycinate for two months after reading countless Reddit posts about how it transformed people's sleep and anxiety. I took 400mg of elemental magnesium (confirmed from the label — this was a reputable brand with third-party testing).
My sleep did not noticeably change. I already sleep reasonably well (7-7.5 hours, falling asleep within 15 minutes), so perhaps there was not much room for improvement. My Whoop data showed no meaningful change in sleep efficiency, deep sleep, or HRV.
My anxiety, which is mild and situational, did not change. I did not feel calmer, less reactive, or more relaxed.
The only things I noticed: my exercise-related calf cramps decreased somewhat (I run 30 miles per week), and I felt slightly less sore after hard workouts. These are real but modest benefits.
I think the enthusiasm for magnesium glycinate is driven by the large number of people who are genuinely deficient and experience significant improvements when they replenish their stores. If you are not deficient — if your diet is good, you do not drink much, you are not on depleting medications — the effect may be minimal. My bloodwork showed my RBC magnesium was already in the upper half of the normal range.
Not saying it does not work. Saying it does not work for everyone, and the "life-changing" reports are selection bias from the deficient population. Worth trying, but manage your expectations if you already eat well and sleep decently.