Is there drug interaction between topomax and zyrtec (cetirizine)? both say take at night

No interaction: Those 2 meds are safe to take together. They both have a slight chance of causing drowsiness, hence the advice to take both at night. Good luck!

Drug interactions.: You can use a drug interaction checker whenever you have questions about drug-drug interactions or drug - food interactions. Here is 1 option (Drugs.Com): https://www.drugs.com/drug_interactions.php Your pharmacist is also a good source of info.