Pertussis
"Taking 500 mg twice a day for pertussis(whooping cough). While I do feel some relief from the pertussis, there are some nasty side effects to it.

Firstly. Horrible GI symptoms. The medication causes a horrible taste for several hours after taking it, and it was causing abdominal pain and a feeling of too much acid in my stomache and an uncomfortable pressure only relieved by vomitting. The GI symptoms were unbearable, but I found eating cheese immediately before swallowing the pill helpped immensly. I also started a probiotic and prilosec for the stomache acid. 

Another issue was extreme muscle weakness (knees buckling) and loss of balance and coordination. I&#039;m 21 with an athletic build and never had this issue before."