Common allergy treatments are generally well-tolerated by most people. Some common side effects may include, but are not limited to: drowsiness, headache, abdominal pain, nausea, dry mouth/nose/throat, cough, nausea or vomiting, or an increase in eye pressure.
The benefits and risks of these treatments must be discussed with a licensed healthcare practitioner doctor, and if you are ever having any side effects, please discuss directly with them.