iirc one of the drug’s effects is not being able to feel emotions you felt before, which is why he doesn’t get happy, sad, angry, etc. but the mc is possibly in love rn, which is a new emotion for him. this is why i think he can make new facial expressions again
So is him not being able to smile a trauma response like the exposure to light or is it the side effect of the drug cause i swear he just smiled.