Don't be fooled. In general, I'm not very enthusiastic about these drugs. They're designed to treat the itching and sneezing that goes along with hay fever, and will stop a runny nose with their drying effects. But then you're stuck with the dryness, and sometimes, sedation, depression, and fatigue. Plus, you're probably still congested.
Headaches can also be a side effect.
I know how annoying allergies can be. But these drugs simply suppress the problem - perpetuating disease, instead of solving it. It will relieve allergy symptoms readily in most people, and has no toxicity. Instead of side effects, you get bonus trace minerals. The best form to buy is a freeze-dried extract of the leaves, sold in capsules.