Short answer: No trial has compared these two forms. Magnesium citrate was better absorbed than magnesium oxide in several human studies.12 Magnesium glycinate has few trials of its own; in one, 250 mg a day modestly eased insomnia symptoms over 4 weeks.3 High supplement doses of any form can cause diarrhea, and magnesium is a key ingredient in some laxatives.4
| Magnesium citrate | Magnesium glycinate | |
|---|---|---|
| Absorption evidence | Higher than magnesium oxide in three human studies, measured by blood and urine magnesium512 | No human absorption study found in the sources checked |
| NIH view of the form | Among the forms that tend to be better absorbed than oxide and sulfate4 | Not named in the NIH list |
| Trials of the form | Mainly absorption studies | Insomnia trial in 155 adults; 12-month trial in 224 people with asthma or COPD and low magnesium36 |
| Sleep | No sleep trial of this form in the sources checked | Small benefit on an insomnia score at 4 weeks3 |
| Side effects | High supplement doses of magnesium can cause diarrhea, nausea and cramping4 | Same NIH warning applies; no serious side effects in the lung trial6 |
NIH says forms that dissolve well in liquid are absorbed better, and that aspartate, citrate, lactate and chloride tend to be absorbed better than oxide and sulfate.4 In a 60-day trial in 46 healthy adults taking 300 mg of magnesium a day, citrate gave the highest blood levels; both citrate and an amino acid chelate beat oxide on urine magnesium, and oxide did no better than placebo.1 Two smaller studies also found citrate better absorbed than oxide.52
In 155 adults with poor sleep, 250 mg of elemental magnesium a day as bisglycinate lowered an insomnia score slightly more than placebo at 4 weeks. The effect was small, and other mood and stress measures did not change. One author runs a research company funded by supplement makers.3
In 224 people with asthma or COPD and low blood magnesium, 440 mg a day of magnesium glycinate for 12 months lowered inflammation markers and improved lung function compared with placebo.6 Across all forms, a 2026 review of 12 trials rated the evidence for magnesium and sleep low to very low and did not support it as a routine insomnia treatment.7
No study answers this directly. Citrate has the stronger absorption data; glycinate has a small sleep trial. The NIH upper limit for supplemental magnesium is 350 mg a day for adults, and magnesium can interact with some antibiotics and bisphosphonates.4 This is general information, not personal advice. More detail: the Magnesium Bisglycinate guide.