I would like to know if antihistamines can cause a false positive hiv 4th generation test? I have heard they suppress the immune system. I was on a 12.5 mg dose of Atarax (Hydroxyzine hydrochloride). I took the test while I was on this medicine. I took the test because I had unprotected vagina sex with a man of unknown status. I test negative after 7 MONTHS. Please let me know about the medication and if there is any interference.