How Does Your Medicine Work?

By Jane Farrell

Medicines can enter the body in many different ways, including through an inhaler, a skin patch, a pill or a hypodermic needle. As drugs make their way through the body, many steps happen along the way. Understanding how medicines work in your body can help you learn why it is important to use medicines safely and effectively. In this section on taking medicines, we’ll focus on medicines you take by mouth, since those are the most common.

Entering and Circulating in the Body

When you take medicines by mouth, they move through the digestive tract and are taken up by internal organs like the stomach and small intestine. Often, they are then sent to the liver, where they might be chemically altered. Finally, they are released into the bloodstream.

As the bloodstream carries medicines throughout the body, the drugs can interact with many tissues and organs. Side effects can occur if a drug has unintended effects anywhere in the body.

Just as it does with food, the body tries to chemically break down medicines as soon as they enter the body. Most drugs taken by mouth enter the stomach or small intestine and then are sent to the liver.

The liver contains protein molecules called enzymes that chemically modify drugs and other non-food substances. The chemical alteration of a medicine by the body is called drug metabolism.

Often, when a drug is metabolized by the body, it is converted into products called metabolites. These metabolites are not usually as strong as the original drug, but sometimes they can have effects that are stronger than the original drug. For example, codeine in the prescription pain killer Tylenol#3 becomes fully active only after the medicine is metabolized in the liver.

Because most drugs and other “foreign” substances are broken down in the liver, scientists refer to the liver as a "detoxifying" organ. As such, the liver can be prone to damage caused by too much medicine in the body.

Drug metabolites often return to the liver and are chemically altered once again before they exit the body.

Exiting the Body

After a drug’s metabolites have circulated in the bloodstream, where they work as medicine, the body eliminates them the same way it eliminates other wastes—in the urine or feces. Age-related changes in kidney function can have significant effects on how fast a drug is eliminated from the body.

Older Adults and Medications

Older people as a group tend to have more long-term, chronic illnesses such as arthritis, diabetes, high blood pressure and heart disease than any other age group. Because they may have a number of health problems or issues at the same time, it is common for older people to take many different drugs. Here are some tips on how to take medicines safely and get the best results from them.

Understanding Your Medication

If your doctor prescribes a medication for your condition, try to find out as much about it as you can, including how to take it properly. Ask the following questions and write down the answers before leaving the doctor's office.

What is the name of the condition this medicine will treat?

What is the name of the medicine?

How does it treat my condition?

What is the name of its active ingredient?

Did you check that it doesn’t contain anything I’m allergic to?

How long will it take to work? How should I store the medication? Does it need to be refrigerated?

Can the pharmacist substitute a less expensive, generic form of the medicine?

Find Out How to Take the Medication

Ask your doctor, pharmacist, or nurse about the right way to take any medicine before you start to use it. Ask questions when you don't know the meaning of a word, or when instructions aren't clear. Here are some specific questions to ask.

Should I take it as needed or on a schedule?

Should I take it at a certain time of day?

How much should I take each time?

Do I need to take it with food?

May I drink alcohol while on this medication?

How long will I have to take it?

Ask What to Expect

How will I feel once I start taking this medicine?

How will I know if this medicine is working?

If I forget to take it, what should I do?

What side effects might I expect? Should I report them?

Can this medicine interact with other prescription and over-the-counter medicines — including herbal and dietary supplements — that I am taking now?

Tips for Taking Medicines Properly

Taking different medicines is not always easy to do properly. It may be hard to remember what each medicine is for, and how and when you should take each one. Here are some tips for taking medicines.

Check the label on your medicine before taking it to make sure that it is for the correct person — you.

Read and save any written information that comes with the medicine.

Take the medicine according to the schedule on the label.

Don't take more or less than the prescribed amount of any medicine.

If swallowing tablets is difficult, ask your doctor or pharmacist whether there is a liquid form of the medicine or whether you could crush your tablets. However, do NOT break, crush, or chew tablets without asking a health professional first.

Get into the habit of checking the expiration dates on your medicine bottles, and throw away medicine that has expired.

Try to set and follow a routine for taking your medicines.

For more information, visit nih.seniorhealth.gov.