Theophylline is another type of bronchodilator that is occasionally used in difficult-to-control or severe asthma. Although it is rarely prescribed, it is sold under the brand names Uniphyl, Theo-Dur, Slo-Bid, and Theo-24, and is available as a pill or liquid. It is long-acting and is used to prevent asthma attacks. Theophylline must be taken daily to be effective. Possible side effects include: - Nausea and/or vomiting - Diarrhea - Stomach ache - Headache - Rapid or irregular heartbeat - Muscle cramps - Jittery or nervous feeling - Hyperactivity