Is it possible for vitamin C in orange juice and ascorbic acid to affect high blood pressure medication?

Yes and no. Vit c in normal doses does not impact BP meds. Orange juice and other sweet liquids (all juice, soda, gatorade, etc) will increase your blood pressure - this will cause a relative decrease in the effectiveness of your meds. Liquids with over 10 cal/serving (except non-fat milk in moderation) are not good for you. Sweets in liquid form increase blood fats, belly fat & ultimately blood pressure.