Norepinephrine, a neurotransmitter as well as a hormone, is related to adrenaline (also referred to as epinephrine), known for its stimulating effects on the body. Norepinephrine is responsible for, among other things, arousal and alertness. For many years it was thought to be the primary neurotransmitter responsible for depression. Reduced levels of norepinephrine may partially explain the apathy seen in individuals with this and other mental disorders. Elevated levels of norepinephrine are strongly associated with anxiety disorders, which frequently coexist with depression.