Can klonopin (clonazepam) and hydroxyzine have a bad interaction?

Be careful: They are both sedatives so if you took sufficiently high doses at bedtime you may cause yourself to stop breathing although in clinical practice that would be rare. As long as you are not taking more than five milligrams of Clonazepam a day then any amount of Hydroxyzine up to about 100 mg a day would likely be tolerated. There are exceptions to these principles so talk to a doctor about this.