How to use Claritin-D 12 Hour. Take this medication by mouth as directed by your doctor, usually twice daily (every 12 hours) with a full glass of water. Claritin (loratadine) is a commonly used allergy medication that is available over the counter. Claritin is indicated to be taken as 10 mg by mouth once daily and it is not recommended to take more than 10 mg over a 24-hour period. What happens if you take 2 Claritin pills per day, one in the morning and the other at night? Alternatively, if he took Claritin D 24 hours (loratadine 10 mg with pseudoehpederine 240 mg) then there is more concern. The pseudoephederine will increase his blood pressure and heart rate. In this case, if he experiences chest pain, trouble breathing, or a severe headache you should call your 24-hour nurse line. He may need to be seen at urgent care. These side effects are unlikely, however. You should be fine but really you are only suppose to take them one a day. Try to stick to that schedule. Join Claritin Blue Sky Living ® to have your local, 4-day weekend pollen forecast sent to you every Thursday. JOIN FOR FREE The information on this site is intended for healthcare professionals in the United States and is not intended for the general public. Hi. Pls do not double dose. Says ten milligrams for ages six and over once a day. Does say if u r over 200 lbs u can take two. Have you ever tryed zyrtec. If you ask me, it is perfectly safe to take more than 10 mg a day. But I'm not your doctor, I have no idea what other medications you take and why you take this at all to begin with. So please put this in proper context.