Sympathomimetics are a class of drugs whose properties mimic those of a stimulated sympathetic nervous system. As such they increase cardiac output, dilate bronchioles, and usually produce constriction of blood vessels. Sympathomimetics include the naturally occurring substances adrenaline (epinephrine), noradrenaline (norepinephrine), and other catecholamines such as dopamine, as well as the synthetic drugs pseudoephedrine, phenylephrine, and phenylpropanolamine. In medicine, they are commonly prescribed in cardiac emergencies including shock and anaphylaxis, in some cases for weight loss, and in cold remedies, where they shrink swollen membranes in the upper respiratory tract . In recent years, phenylpropanolamine has been removed from over-the-counter cold formulations after it was implicated in causing an increased risk of hemorrhagic stroke.