Vitamin C is safe and inexpensive. As an antioxidant, it has a plausible mechanism for influencing the course of neurodegenerative diseases. Two flawed preclinical studies by the same group showed benefits in a mouse model of familial ALS. There are two case reports in which it was associated with improvement. However, there are multiple possible explanations for the improvement in these cases. It is not clear which if any dose of vitamin C might be beneficial for PALS; a small clinical trial using oral vitamin C at 2,000 mg daily was unable to demonstrate benefits in PALS. Based on this negative trial, we currently advise against using vitamin C to treat ALS.