Beta blockers are a class of pharmaceutical commonly used to treat arythmia, for protection of the heart after a heart attack and high blood pressure. They work by suppressing the effect of adrenaline and other stress hormones. They were first developed in the 1950s. One of their most useful side effects is the reduction of social anxiety, and they are occasionally prescribed for this purpose. Common side effects are nausea and diarrhea. Less common are hallucinations, insomnia, nightmares, fatigue and impotence