How long does it take to develop tolerance to zyrtec? how often would i have to take it to become tolerant? i take cetirizine hcl (10 mg) for my eczema flare ups, and i was worried the pills would lose its effectiveness if i took them too often?

This is not one of the drug types that are rendered less effective with use. Eczema has a common pattern of mixed flare ups & improvements over time that may lead someone to think meds are less helpful. I would use it as you need it and have a plan that includes alternative treatments when the expected flare ups occur.

Eczema: It varies with each individual person. Some can take it for a long period of time and still effective . Some people have to switch up for a month and then go back to Zyrtec without problems. You can also alternate to Allegra. You can easily tell which ones works best for you! Make sure to take your meds till you are 2 weeks symptom free to get full benefit!