Ok, so pretty much anyone can buy it without any trouble/questions? What's the cap?
With all that said, the daily limit of pseudoephedrine that may be purchased is 3.6g. This means that you cannot buy more than 15 of the aforementioned tablets in one day. Note that they are typically sold in packs of 5, 10, and 15. Exceptions are not made for the fact that you may be going on a vacation, or that it is difficult for you to get to the store, so don't give the clerk a hard time. In the case of a large chain drugstore, their computer will simply lock out the sale. In the case of a small independent drugstore, the shopkeeper is theoretically obligated to make a "good faith" effort to check the logbook to ensure that you are not over your daily limit. Obviously this has its shortcomings.
In addition to a daily limit, there is also a 30-day limit on what you can buy. You cannot buy products containing more than 9g of pseudoephedrine in any 30-day period. This actually works out to 37 tablets, but since they aren't commercially available in smaller quantities than 5, it means that you can't buy more than a 35-day supply within 30 days. Again, this can be burdensome if you are going away on vacation to a place where it will not be available, or if you live in a remote area