Cannabinoids have been found to have antioxidant properties, unrelated to NMDA receptor antagonism. Here's a document that shows that the US Government represented by the Department of Health and Human Services was granted patent for use of cannabinoids as antioxiants and neuroprotectants.
Since the US Government is hand in gloves with the big pharmaceutical firms, it will not allow this simple natural treatment line to cure serious diseases. From another article, discussing the same patent in detail, here's the conclusion:
"It has surprisingly been found that cannabidiol and other cannabinoids can function as neuroprotectants, even though they lack NMDA receptor antagonist activity. This discovery was made possible because of the inventor's recognition of a previously unanticipated antioxidant property of the cannabinoids in general (and cannabidiol in particular) that functions completely independently of antagonism at the NMDA, AMPA and kainate receptors. Hence the present invention includes methods of preventing or treating diseases caused by oxidative stress, such as neuronal hypoxia, by administering a prophylactic or therapeutically effective amount of a cannabinoid to a subject who has a disease caused by oxidative stress."