Can caffeine and antihistamines have an affect on Hair Transplant Graft survival and the final outcome?

I know both of these constrict blood vessels and blood supply so would this cause any harm (I am 16 days post op)? I have read that things like smoking and cocaine use can have negative effects due to their vasoconstriction so would these act the same? I like coffee a few times a day and usually take an antihistamine for allergies but if it will effect the outcome of the grafts surviving I am willing to do without coffee and deal with the allergies for a while.