Both Theophylline and Salbutamol are known to have nasty side effects, especially when taken in the high doses that are recommended as a therapy of first recourse for SCLS.
The former medication often causes caffeine-like adverse effects such as nausea, vomiting, headaches, irritability and insomnia; it can also cause the heart to beat too fast or in an irregular manner. However, some of these side effects can be temporary and they depend on the dosage you are taking.
The latter medication has many of the same side effects: tremors, nervousness, headaches, muscle cramps, dry mouth, palpitations, and a rapid heart rate. Therefore, Theophylline and Salbutamol tend to reinforce each other -- for better and for worse.
The dosages of course can be modified: the prudent approach is to start with a low dose, monitor the side effects, and as your body gets used to these medications, raise the dosage. Some patients cannot tolerate them, at least not without taking a tranquilizer at the same time.
Moreover, these medications appear to work for some patients and definitely don't work for others. Therefore, in recent years, SCLS patients in Europe and now North America are being migrated to IVIG therapy, which has fewer side effects and is delivering consistently better results.
For a flavor of the discussion here in this Community, check out the posts titled "Theophylline-Pure Concentrated Evil!," "Terbutaline vs. Theophylline," "IVIG 2011," and "On IVIG as the Best Therapy."