After taking my first dose, the itching is gone, but now feel very drowsy, I think it's the medicine taking effect, I google and found that this drug have quite a number of side effects: Source Cetirizine side effects Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Stop using cetirizine and call your doctor at once if you have any of these serious side effects: fast, pounding, or uneven heartbeat; weakness, tremors (uncontrolled shaking), or sleep problems (insomnia); severe restless feeling, hyperactivity; confusion; problems with vision; or urinating less than usual or not at all. Less serious side effects may include: dizziness, drowsiness; tired feeling; dry mouth; sore throat, cough; nausea, constipation; or headache. I think I'm feeling weakness, eyes blurry, drowsy, tired, dry mouth, if I can still type I guess i