Methods and compositions for protecting muscarinic receptor(s) in a subject from at least one carcinogenic or toxic metal by administration of a pyrophosphate analog. Methods and compositions for preventing at least one disease induced or caused by metals compromising the function of muscarinic receptors in a subject by administration of a pyrophosphate analog. Methods and compositions for reducing toxic action of metal ions and for reducing poisoning by metals by administering a pyrophosphate analog.