Loratadine works for 12 hours, not 24 as directed by box.

Patient: I am 19 years old, 5’9 and weigh 115 lbs.I was prescribed by my doctor to take Loratadine 10mg and have been taking it since I was 17. It has now been two years and now when I take Loratadine, most of my symptoms go away and I feel a lot better in a matter of minutes. It is supposed to last 24 hours, but after sleeping and waking up the next day, the symptoms feel as if they have returned.It has not been 24 hours yet, but I want to take another tablet. What would you recommend?

Symptoms: Sneezing, runny nose, congestion, and sinus pressure.