Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
severe or continued vomiting;
ongoing headache, trouble sleeping;
rapid heartbeats;
a seizure;
new signs of illness (especially fever);
low potassium level--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling; or
high blood sugar--increased thirst, increased urination, dry mouth, fruity breath odor.
Serious side effects may be more likely in older adults.
Common side effects may include:
nausea, vomiting, diarrhea;
headache;
sleep problems (insomnia);
tremors;
sweating; or
feeling restless or irritable.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Theophylline side effects (more detail)
