I am a biohacker type who likes to test things systematically. After reading about the differences between magnesium forms, I decided to test three of the most common ones head-to-head, each for one month, all at 200mg of elemental magnesium, taken at 9 PM before bed. I tracked sleep with an Oura ring and kept a daily subjective log.
Month 1 — Magnesium Oxide: The cheapest form. GI effects were immediate and brutal. Loose stools within 45 minutes of taking it, almost every night. This alone made it miserable. Sleep data showed minimal change from baseline — deep sleep actually decreased slightly, though that could be because I was waking up to use the bathroom. Subjective feeling: nothing positive. Would not recommend at all.
Month 2 — Magnesium Citrate: Much better tolerated than oxide, but I still had noticeably looser stools, especially in the first week. Sleep improved slightly — about 8 minutes faster sleep onset on average, and a modest increase in deep sleep (55 min to 62 min average). The laxative effect never fully went away. Some people want this; I did not.
Month 3 — Magnesium Glycinate: Zero GI issues from day one. None. This alone makes it the winner for me. Sleep onset improved the most of any form — averaging 10 minutes versus my baseline 22 minutes. Deep sleep increased from 55 minutes to 73 minutes average. I felt subjectively calmer during the day, particularly in the evenings. Less muscle tension. The overall effect was subtle but consistent.
The glycinate form was the clear winner in every category except price (it costs about twice as much as oxide per serving). But given that oxide is basically throwing money away due to its abysmal absorption rate, the price per milligram of actually absorbed magnesium makes glycinate the better value anyway.
One important note: these results are n=1 and should be taken accordingly. But they align with the research on relative bioavailability, and my experience matches what most people on r/Supplements report when they compare forms.