The answer to that depends on whether your dose is prescription strength or over the counter strength. The answer also depends on your weight. If you are over 200 pounds, sometimes 2 tablets is really the effective dose. While homeboy above me is mostly correct, he is not totally correct. They also have to make sure the dose is safe for 12 year olds that weigh 100 pounds to get the correct labeling. And while there are only a certain number of sites (correct), taking more increases the odds that those receptors remain blocked from the effects of histamine. Risks of taking too much (overdose levels) include liver and kidney issues.
Let's ask Mr. Pharmacologist to read a little about the clinical trials and comments from the FDA (link attached).
You may want to consider another third generation H1 antagonist like Zyrtec. Zyrtec is now offered over the counter. This medication has a greater affinity for the H1 (histamine) receptor and is typically more effective than Claritin. Some populations find that Zyrtec works but it makes them a little drowsy. For some, drowsy is a lot better than snotty, sneezy, wheezy, and miserable.