The only medications that cause permanent or indefinite deferral from blood donation are Tegison (psoriasis), growth hormone (from human pituitary glands), and insulin from cows (imported). Other meds may have a wait period until you can donate, maybe unless your history is suspicious to the person asking the questions.

Blood donation does not negatively affect immunity in healthy persons nor does it improve immune health. Persons with decreased immunity are not allowed to donate.