Conclusion: Magnesium oxide and naldemedine are most likely effective for prevention of OIC in cancer patients. Naloxone in a fixed combination with oxycodone, naldemedine and methylnaltrexone effectively treat OIC in cancer patients with acceptable adverse events. However, their effect has not been compared to standard (osmotic and stimulant) laxatives. More studies comparing standard laxatives with each other and with opioid antagonists are necessary before recommendations for clinical practice can be made.
Magnesium Oxide side effects
Across 174 first-hand reports, people mentioned a side effect 71 times (about 41 per 100 reports). The most common: diarrhea, stomach issues, laxative effect. User reports show what people notice — they can't tell you whether Magnesium Oxide is safe for you.
Reported side effects
diarrhea31
stomach issues22
laxative effect9
insomnia3
brain fog2
vivid dreams2
stomach pain1
increased heart1
What got worse for some people
In their own words
“I've tried various forms of magnesium over the past year including threonate, glycinate, citrate, oxide, and taurate. They all give the same negative side effects.”
“I was taking crappy magnesium oxide supplements for years with basically no effect, besides diarrhea if I took too much magnesium oxide. Magnesium oxide has basically no bioavailability.”
“If it's oxide, which has 4-5% bioavailability, will probably do nothing for you like it does for me.”
“Oxide has shit bioavailability but that didn't bother unless I too ka fairly large dose, it's basically a diuretic.”
“I feel emotionally blunted when I take magnesium during the day, but it's great at night.”
“I'm taking 250mg of magnesium oxide twice daily to see if it could help with my depression/anxiety/fatigue combo. Well, it has.”
Is Magnesium Oxide safe? What the research covers
AResearch: Strong24 meta-analyses · 81 randomized trials on PubMed
Cancer Treat Rev · 2024
Pharmacological prevention and treatment of opioid-induced constipation in cancer patients: A systematic review and meta-analysisLancet Child Adolesc Health · 2025
Efficacy and safety of pharmacological therapies for functional constipation in children: a systematic review and meta-analysisConclusion: Polyethylene glycol is probably more effective than placebo and key comparator therapies and should be considered the standard of first-line care. Future studies should consider polyethylene glycol as an index therapy, and clearly describe methods, patient characteristics, and previous therapeutics.