How do you take your medicine for allergy? Do you take it with water or juice? Experts advise to take it water because flavonoinds in the juices block the drug from entering the bloodstream. Scientists have discovered that juice from apples, oranges or grapefruit can reduce the body's absorption of fexofenadine, an anti-histamine, making it less effective. Next time you have an allergy, take your meds with water for best results.