My 13 year old son was taking Singulair for several years and had...

My 13 year old son was taking Singulair for several years and had developed, over time, depression and anxiety. I didn't put the two together until the news stories came out a couple of years ago. Since then he has been taking Zyrtec. Over time the depression and anxiety has returned. He does not take the Zyrtec everyday, just as needed. I believe that it has built up in his system to cause the side effects. Can anyone give me an idea of how long it takes to get out of his system so that I can tell if this is what is causing the problems or if I should look for some other cause. Thanks