Is it ok to take claritin (loratadine) in the morning and zyrtec at night?

No additional benef: Since both of these meds work in very similar ways, there is likely to be very little additional benefit from using both, and much more likely to have side effects from the meds. if one alone is not working, talk to doc about what combination therapy may be more useful, including use of prescription med like Singulair (montelukast). Also need to delve into allergen prevention so you won't need as much meds.