Endorphins are neurotransmitters found in the brain that have pain-relieving properties similar to morphine.

Three Major Types of Endorphins
Beta-endorphins, found primarily in the pituitary gland
Enkephalins and Dynorphin - both are distributed throughout the nervous system.

Endorphins interact with opiate receptor neurons to reduce the intensity of pain among individuals afflicted with chronic pain disorders, endorphins are often found in high numbers.

Many pain-killing drugs, such as morphine and codeine, act like endorphins and actually activate opiate receptors.

Besides behaving as a pain regulator, endorphins are also thought to be connected to physiological processes including euphoric feelings, appetite modulation, and the release of sex hormones.

Prolonged, continuous exercise contribute to an increased production and release of endorphins, resulting in a sense of euphoria that has been popularly labeled ‘runners high’.

When a person inhales cigarette smoke, the nicotine in the smoke is rapidly absorbed into the blood and starts affecting the brain within 7 seconds. The result is the release of the hormone adrenaline, the "fight or flight" hormone. Physically, adrenaline will increase a person's heart rate, blood pressure and restrict flow to the heart muscle. The smoker will experience rapid, shallow breathing. Adrenaline also instructs the body to dump any excess glucose into the bloodstream.

It is thought that nicotine inhibits the release of the hormone insulin, which is responsible for removing excess sugar from a person's blood. The result can be that the smoker is slightly hyperglycemic, meaning they have more sugar in their blood than usual. High blood sugar acts as an appetite suppressant, which may be why smokers think their cigarettes reduce hunger. In the long run though, nicotine in the bloodstream increases the "bad" LDL cholesterol, which is thought to clog and harden arteries. That in turn will step up the risk of heart attack and stroke.

The nicotine molecule is very similar in shape to the neurotransmitter acetylcholine, which affects many bodily functions, including breathing, heart rate, learning and memory. Acetylcholine in turn also affects other neurotransmitters that have influence over appetite, mood, and memory. When nicotine gets into the brain, it attaches to nerve cells in places where acetylcholine would, creating the same effects.