It's pretty well documented that over the counter pain killers such as acetaminophen, aspirin, and ibuprofen can have long term negative consequences with long term use. Allergy meds appear to be joining this group. In many cases the threshold for harm is fairly low in terms of lifetime cumulative dose. In some cases there are long-term benefits to these drugs(aspirin for instance) but there are definitely downsides. That isn't to say that pursuing alternative treatments to colds and allergies makes sense.