Glycine appears to be safe, even at doses of up to 9 grams for 3 days. But glycine's safety has not been fully tested or studied. Particular caution should be taken when considering glycine for young children, pregnant or breastfeeding women, and people with liver or kidney disease.
People being treated with clozapine (Clozaril, Versacloz) should avoid taking glycine. Also people who have had a stroke should not take glycine without the supervision of a doctor.