This is so funny because of how long a chain of telephone it is. The starting point is that grapefruit juice SPECIFICALLY can interact negatively with several mental health medications (notably, not amphetamines). Then this tumblr post* and MULTIPLE NEWS ARTICLES got popular, stating that consuming anything acidic (including vitamin C) within an hour of taking your ADHD meds would render them ineffective. In reality, a large dose of vitamin C taken directly with an amphetamine-based ADHD medication has the potential to cause a minor dampening effect, but has no effect on other ADHD meds.
These presumably got filtered/combined into the idea that vitamin C is bad to take with ANY mental health meds, which then got turned into the idea that if you have mental health problems, scurvy may be right for you!