Magnesium bisglycinate is magnesium chelated to the amino acid glycine.
It supports normal magnesium status, and it is the form used in the one randomised trial listed below that tested the chelate itself, a 4 week study in pregnant women with leg cramps at 300mg/day (Supakatisant 2012).
The tolerability and absorption advantages usually attributed to this form are not well established.
The single controlled head to head on tolerability, in 12 patients with ileal resection, reported the chelate was better tolerated than magnesium oxide (Schuette 1994), and a crossover study in 40 healthy adults found no significant rise in plasma magnesium after bisglycinate at any sampled time point while oxide and citrate did rise (Pajuelo 2024).
Glycine is an inhibitory neurotransmitter in the central nervous system, but no study listed here tested whether the glycine in the chelate contributes to sleep or calm, so that mechanism remains an inference rather than a finding.