Side effects are usually minor, but if your ankles start to swell or you have an allergic reaction or trouble breathing, call your doctor
In addition to this, many people have problems metabolizing B12 in low-quality forms like cyanocobalamin due to defects in the MTHFR gene (1) (as many as 40% of people have THIS problem!)
In these cases all the glutathione produced by the liver is used to try to eliminate these poisonous substances, and there is not enough left for the needs of the other organs
PMID 9546215
10.1161/01.RES.0000200177.53882.c3 62 KimN
One survey found that over 62% of individuals supplementing with intranasal glutathione reported health benefits for either multiple chemical sensitivities, allergies, sinusitis, Parkinsons disease, Lyme disease, or fatigue