Taking vitamin c when you're sick doesn't do anything to help you, really. Potassium can in some cases, if your reaction to the illness is doing something to cause you to lose potassium (sweating, vomiting, etc) but for just a cough probably won't make a difference.
MissApocalycious t1_j2dx7ql wrote
Reply to comment by Duradon in ELI5. Why is honey and lemon a popular cure for cold like symptoms. What makes lemon more effective than say an orange or lime? by alexkid_in_realworld
Taking vitamin c when you're sick doesn't do anything to help you, really. Potassium can in some cases, if your reaction to the illness is doing something to cause you to lose potassium (sweating, vomiting, etc) but for just a cough probably won't make a difference.