**Hypercholesterolemia** means that the cholesterol level is too high in the blood.

Cholesterol
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See the main article: Cholesterol
Cholesterol is a molecule in cells. It is a type of lipid which is a fat or fat-like molecule. Cholesterol is a special type of lipid that is called a steroid. Steroids are lipids that have a special chemical structure. This structure is made of four rings of carbon atoms.

Other steroids include hormone steroids like cortisol, estrogen, and testosterone. In fact, all steroid hormones are made from changing the basic chemical structure of cholesterol. When scientists talk about making one molecule from changing simpler ones, they sometimes call it *synthesis*.

Jobs
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Cholesterol does many important jobs in a cell. Cholesterols main function is as a structural component of cell membranes. It is also the starting material for bile acids that are made by the liver and used to digest fats, and for steroid hormones. However, it is best known for something bad that it does. High levels of cholesterol can lead to atherosclerosis. This is an inflammatory disease of artery walls in which white blood cells invade the vessel wall and become engorged with cholesterol and other lipids. These 
areas can slowly close off a blood vessel or can suddenly rupture and trigger formation of a blood clot.

Types
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Not all cholesterol is bad. There are different kinds of cholesterol in the blood. Doctors often measure these different types to see if someone has hypercholesterolemia.

HDL (high density lipoprotein) is sometimes called 'good cholesterol' because people with high levels of HDL cholesterol have *less* atherosclerosis.

LDL (low density lipoprotein) is sometimes called 'bad cholesterol' because people with high levels of LDL cholesterol have more atherosclerosis.

High blood levels of VLDL (very low density lipoprotein) also causes more atherosclerosis. However, measuring its level in blood is more expensive. So the blood level of triglycerides (a kind of fat) is used instead. High triglycerides (TG) are found in people with high VLDL.

Treatment
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The most common type of medicine to treat hypercholesterolemia are 'statin' drugs. They are called 'statins' because their names all end in -statin. They are also called *HMG-CoA Reductase Inhibitors*. This is because they work by *inhibiting* the enzyme HMG-CoA Reductase. Inhibiting an enzyme means to make it work less well.

The HMG-CoA Reductase enzyme causes the body to make more cholesterol. If it is inhibited, the body makes *less* cholesterol. So statin drugs lower the amount of LDL (bad) cholesterol in the blood which stops atherosclerosis from getting worse. Statin drugs can even help make atherosclerosis better. However, statins are not as good at increasing the HDL (good) cholesterol. Low HDL is hard to treat with medicines, but goes up with more exercise.

There are two big problems with taking statins: Liver problems and 'Rhabdomyolysis.'

Rhabdomyolysis means a disease where muscle cells are damaged and die. Statins can cause damage to muscle cells. This can cause weakness and muscle pain. The worse problem though is that when muscle cells die, they release cell proteins into the blood. The kidney removes the muscle protein from the blood. If the kidney takes up too much protein, it can be hurt. If it is bad enough it can cause kidney failure. So if people take statins and get muscle pain or weakness, stop the medicine and see a doctor.

Statins can also cause liver problems. They can cause mild irritation of the liver. They can rarely cause very bad liver damage. Because of this, when someone starts taking a statin, doctors check liver blood tests after six weeks. Doctors also warn patients to watch for the signs of liver damage: pain in the right side of the abdomen, nausea, vomiting, and jaundice.

However, both of these problems are *rare*. In someone with hypercholesterolemia, the benefit from statins is more than the risk. This means that someone is more likely to prevent problems than cause problems by taking them. There are many big scientific studies of this problem that show the same thing: if people have hypercholesterolemia and take statins, *they are more likely to live longer and be healthier*.

There are other kinds of medicines to treat hypercholesterolemia. But statins are the most effective treatment.

*Fibrates* are medicines that lower cholesterol levels. They may also help people with Type II Diabetes. This is a good effect because diabetes and hypercholesterolemia cause some of the same problems. If both diabetes and hypercholesterolemia happen in the same person the problems from these diseases can be much worse. Fibrates can have rhabdomyolysis like the statins and also can cause upset stomach. Use of fibrates and statins at the same time makes rhabdomyolysis happen much more often.

Niacin is a vitamin that lowers cholesterol levels. It is also called Vitamin B3 or nicotinic acid. Severe niacin deficiency in the diet can cause a disease called *Pellagra*. This is rare in the developed world today. However, less bad deficiency of niacin can cause high blood pressure, weight gain, and hypercholesterolemia. So sometimes Niacin is used to treat hypercholesterolemia. Niacin is one of the medicines that may make HDL (good) cholesterol go up. The biggest problem with taking enough Niacin to help cholesterol is that it causes severe *flushing* (hot, red, sometimes itchy skin). This 'side-effect' is so bad, sometimes people stop taking the medicine.

Bile Acid Resins are medicines that make people not absorb as much bile when they digest food. This causes them to take up less cholesterol also, which lowers blood levels of cholesterol.