Many users who buy Salmeterol drug supplies will have little or no side effects. However, adverse reactions are a possibility. The most common minor side effects are headaches, sinus congestion, increased nervousness, irritation of the throat, or tremors. Other side effects that should be immediately referred to emergency medical personnel include the following: chest pain, abnormal heart rate, increase in asthma symptoms, difficulty breathing, severe headaches, muscle cramping, choking, fevers, or symptoms of an allergic reaction.