Sometimes it seems like there are more medicines than there are diseases. Some medications can be bought over the counter at pharmacies or other stores. Others require a doctor's prescription. A few medicines are available only in hospitals. Medicines can cure, stop, or prevent disease; ease symptoms; or help in the diagnosis of certain illnesses.

What Are Medicines?
Medicines are chemicals or compounds used to prevent or treat diseases and the symptoms you might have as a result of those diseases. Think about it: the body is made up completely of chemicals. Some are simple; others are more complex. When some of the body's chemicals get out of whack, other chemicals in the form of medicines can get them back on the right track. During the past century, advances in medications have enabled doctors to cure many diseases and save lives.

These days, medicines come from a variety of sources. Many have been developed from substances found in nature, and even today many are extracted from plants. For example, one medicine that is used to treat cancer comes from the Pacific yew tree. Some medicines are produced in a laboratory by mixing together a number of chemicals; others, like penicillin, are a by-product of organisms such as fungus or bacteria. And a few medicines are even biologically engineered by inserting genes into bacteria that make them produce the desired substance.

Ever feel like you only have two options - shot or pill - when it comes to taking a medicine? The truth is, there are many ways in which medications can be delivered other than pills or shots:

• liquids that are swallowed (like cough syrup)
• drops (which are put into the ears or eyes)
• creams, gels, or ointments (which are rubbed onto the skin)
• inhalers (like nasal sprays that are squirted into your nose or asthma inhalers that are breathed in through your mouth)
• patches (which are stuck to your skin and are called transdermal patches)
• tablets that are placed under the tongue (these are called sublingual medicines; the medication is absorbed directly into blood vessels and enters the bloodstream) 

No medicine can be sold for use unless it has first been approved by the U.S. Food and Drug Administration (FDA). The manufacturers of the medication perform tests on all new medicines and send the results to the FDA. The FDA allows new medicines to be used only if they work and if they are safe enough. When a medicine's benefits outweigh its known risks, the FDA usually approves the sale of the drug. The FDA can withdraw a medication from the market at any time if it later is found to cause harmful side effects.

Different Types of Medicines
Doctors have lots of choices when it comes to finding the best medication to make a sick person feel better. Medicines act in a variety of ways. Some medicines can cure an illness by killing or halting the spread of invading germs, such as bacteria and viruses. Other medicines are used to treat cancer kill cells as they divide or prevent them from multiplying. Some drugs simply replace missing substances or correct abnormally low levels of natural body chemicals such as certain hormones or vitamins. Medicines can even affect the part of the nervous system that controls a particular body process. For instance, most medicines taken to relieve vomiting act on the vomiting control center in the brain.

Nearly everyone has taken an antibiotic. This type of medicine fights bacterial infections. Your doctor may prescribe an antibiotic for strep throat or an earache. These medicines work either by killing bacteria or halting their multiplication so that the body's immune system can fight off the infection.

Sometimes a part of the body can't produce enough of a certain chemical. That can also make you sick. Someone with insulin-dependent diabetes, for instance, has a pancreas that can't produce enough insulin. Some people have a low production of thyroid hormone, which helps control how the body uses energy. In each case, doctors can prescribe medicines to replace the missing chemical.

Some medicines treat symptoms but can't cure the illness that causes the symptoms. (A symptom is anything you feel, such as a cough or nausea, while you're sick.) So taking a lozenge may soothe a sore throat, but it won't kill that nasty strep bacteria. Certain medicines are designed to relieve pain. If you pull a muscle, your doctor might tell you to take ibuprofen (like Advil) or acetaminophen (like Tylenol). These analgesics (pronounced: ah-nuhl-jee-zicks, or pain relievers) don't get rid of the source of the pain - your muscle will still be pulled. What they do is block the nerve pathways that transmit pain signals from the injured or irritated body part to the brain (in other words, they affect the way the brain reads the pain signal) so that you don't hurt as much.

As adults get older, they sometimes develop chronic or long-term conditions. Medicines can help control certain conditions like high blood pressure or high cholesterol. Like pain relievers, these drugs don't fix the basic problem, but they can help prevent some of the body-damaging effects of the disease or condition over time.

Among the most important medicines are immunizations. These keep people from getting sick in the first place by immunizing, or protecting, the body against certain infectious diseases. Vaccines contain parts or products of infectious organisms or whole germs that have been modified or killed. When a vaccine is given, it primes the body's immune system to fight off infection by that germ. Most immunizations that prevent you from catching diseases like measles, whooping cough, and chicken pox are given by injection. No one thinks shots are fun. But when your friends all have the flu and you don't, thanks to your flu shot, that injection isn't so bad.

Although no one can get certain medications without a prescription, store shelves are filled with treatments intended to relieve symptoms such as pain, cough, or upset stomach. But just because a medicine is available over-the-counter (OTC), that doesn't mean it's free of side effects. You need to take over-the-counter medicines with the same caution as those that are prescribed by your doctor.

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