Supporting a Friend in Behavioral Health Hospital

tw? talk of mental hospitals . . . hey, so my best friend since high school just went to the behavioral health hospital in my town. aaaand they're not great. he's been there 2-3 times before and everytime he's went its only made him worse. they don't take his allergies seriously enough to make sure there's no cross contamination. meaning that he can barely keep anything down. not to mention the fact that his chronic illnesses just act up while he's under stress and the only thing that helps is either medical cannabis or Zofran, which makes him a zombie. we both have BPD although his can be more explosive. i was wondering what ways i can better support him or advocate for him while hes in this high stress situation.