How Drugs Work in Your Body

Drugs work in your body in a variety of ways. They can interfere with microorganisms (germs) that invade your body, destroy abnormal cells that cause cancer, replace deficient substances (such as hormones or vitamins), or change the way that cells work in your body.

There are more than 8,000 medications available either by prescription or over-the-counter. Some can be used to treat several different health conditions. Aspirin, for example, can be used to treat pain, inflammation, and fever. In addition, aspirin can prevent heart attacks if taken on a regular basis.

The following information is a basic overview of how some drugs work to improve your health.
Fighting Infections
An infection occurs when microorganisms, such as bacteria or viruses, invade your body. Medications used to treat infections can kill germs directly or prevent them from multiplying and growing.


Some medications used to treat infections include:
Augmentin (amoxicillin/clavulanic acid), used to treat ear infections
Bactrim (trimethoprim-sulfamethoxazole), used to treat urinary tract infections
Lamisil (terbinafine), used to treat ringworm
Pen-Vee K (penicillin), used to treat strep throat
Valtrex (valacyclovir), used to treat herpes infections
Targeting Cancer Cells
There are three types of medications used to treat cancer. Chemotherapy attacks cancer cells directly and stops or slows their growth and spread. Biological therapy helps your body’s immune system fight cancer. Lastly, antiangiogenic therapy blocks the growth of new blood vessels to a tumor, which may cut off a tumor's supply of oxygen and nutrients. Some cancers are treated with a combination of these medications.

Some medications used to treat cancer are:
Adriamycin (doxorubicin), a chemotherapy agent used to treat a number of cancers, including bone, breast, stomach, lung, bladder, leukemia and lymphoma
Avastin (bevacizumab), an antiangiogenic therapy used to treat cancers of the colon, rectum, or lung
Intron-A (interferon alpha), a biological therapy used to treat malignant melanoma
Herceptin (trastuzumab), a biological therapy used to treat breast cancer
Platinol (cisplatin), a chemotherapy agent used to treat many types of cancer including bladder, lung, and head and neck
Replacing Missing or Deficient Substances
Your body needs certain levels of amino acids (or proteins), vitamins and minerals to work properly. If these substances are deficient or missing, you can develop health conditions such as scurvy (vitamin C deficiency), anemia (iron deficiency), and pernicious anemia (vitamin B12 deficiency). Recent medical studies have suggest that a lack of vitamin D may increase the risk of heart attack in men. Your physician, therefore, may recommend a vitamin D supplement.


You also can develop a deficiency disorder caused by a lack of hormones in your body. Hormones regulate many of the functions in your body, and a deficiency in one or more hormones can cause serious health problems. Diabetes (insulin deficiency), hypothyroidism (thyroid hormone deficiency), and short stature (growth hormone deficiency) are some examples.

Some medications used to treat hormone deficiency disorders are:
Androgel (testosterone), used to treat hypogonadism (low testosterone in men)
Humalog (insulin lispro), used to treat diabetes
Humatrope (somatropin), used to treat short stature due to growth hormone deficiency
Premarin (conjugated estrogens), used to treat symptoms of menopause
Synthroid (levothyroxine), used to treat hypothyroidism
Changing How Cells Work
Most common chronic diseases -- such as asthma, type 2 diabetes, hypertension, arthritis, heart disease, and some types of mental illness -- are caused by an abnormality in how the cells in your body function. These abnormalities may be caused by aging of cells, genetics, wear and tear on the body, and lifestyle issues such as smoking, lack of exercise, poor eating habits, and environmental stress and pollution.

Most medications prescribed or sold over the counter target one or more of these cell abnormalities. For example, some medications used to treat pain and inflammation interfere with the production of chemical substances that are released by cells in response to tissue damage. These chemical substances, also known as mediators, are responsible for the pain and swelling in arthritis and injuries.

Some medications used to treat depression work by increasing the amount of a chemical messenger in the brain. Additionally, some other medications make cells more or less sensitive to hormones in the body. Beta blockers, such as Tenor min (atenolol) and Toprol XL (metoprolol), are used to treat hypertension by making heart cells less sensitive to the body’s adrenaline. Some oral diabetes medications, such as Actos (pioglitazone) and Avandia (rosiglitazone), make muscle cells more sensitive to insulin.

Some medications that alter the function of body cells are:

Arthrotec (diclofenac, misoprostol), used to treat arthritis
Lipitor (atorvastatin), used to treat high cholesterol
Nexium (esomeprazole), used to treat GERD (heartburn)
Viagra (Sildenafil), used to treat erectile dysfunction
Zoloft (sertraline), used to treat depression

Drug Interactions: Reducing Your Risk

What Is a Drug Interaction?

Drug interactions occur when one drug interacts with another drug that you are taking or when your medications interact with what you eat or drink. Drug interactions can change the way your medications act in your body. Drug interactions can make your medications less effective or they can cause unexpected and potentially dangerous side effects.

Your risk of having a drug interaction increases with the number of prescription and over-the-counter medications that you use. Moreover, the type of medications you take, your age, diet, disease, and overall health can all affect your risk. The elderly are at greater risk for drug interactions than younger adults since a larger proportion of seniors take prescription medications or over-the-counter products.

There are three important types of drug interactions:

Drug-drug interactions occur when two or more drugs interact with each other. Interactions can occur with prescription drugs, over-the-counter drugs, vitamins, and alternative medications such as supplements and herbal products.

Some examples of drug-drug interactions include:
Mixing a prescription sedative to help you sleep with an over-the-counter antihistamine for allergies can cause daytime drowsiness and make driving or operating machinery dangerous.
Combining aspirin with a prescription blood thinner such as Plavix (clopidogrel) can cause excessive bleeding.
Some over-the-counter antacids interfere with the absorption of antibiotics into the bloodstream. Certain medications used to treat fungal infections can cause serious side effects when combined with cholesterol-lowering medications such as Lipton (atorvastatin).
The herbal supplement ginkgo balboa can cause bleeding if taken with aspirin.

Drug-food interactions occur when a drug interacts with something you eat or drink.

Some examples of drug-food interactions include:
Dairy products, such as milk, yogurt and cheese, can interfere with the absorption of antibiotics into the bloodstream.
More than 50 prescription drugs are affected by grapefruit juice. Grapefruit juice inhibits an enzyme in the intestine that normally breaks down certain drugs and hence allows more of a medication to enter the blood stream.
Vegetables containing vitamin K, such as broccoli, kale and spinach, can decrease the effectiveness of drugs, such as Coumadin (warfarin), given to prevent blood clotting.
Mixing alcohol with some drugs is particularly dangerous. Alcohol interacts with most antidepressants and with other drugs that affect the brain. The combination can cause fatigue, dizziness, and slow reactions. A small amount of beer, wine, or liquor can increase your risk of stomach bleeding or liver damage when mixed with over-the-counter anti-inflammatory drugs and medications used to treat pain and fever. These drugs include aspirin, ibuprofen, and acetaminophen.

Drug-condition interactions may occur when a medication interacts with an existing health condition.

Some examples of drug-condition interactions include:
Decongestants, such as pseudo ephedrine found in many cough and cold preparations, can increase blood pressure and may be dangerous for people with hypertension. 
Beta blockers, such as Toprol XL (metoprolol) and Tenormin (atenolol), used to treat high blood pressure and certain types of heart disease can worsen the symptoms of asthma and COPD.
Diuretics, such as Hydrodiuril (hydrochlorothiazide), can increase blood sugar in people with diabetes.
What Can I Do to Help Prevent Drug Interactions?
Before starting any new prescription drug or over-the-counter drug, talk to your primary healthcare provider or pharmacist. Make sure that they are aware of any vitamins or supplements that you take.
Make sure to read the patient information handout given to you at the pharmacy. If you are not given an information sheet, ask your pharmacist for one.
Check the labels of your medications for any warnings and look for the "Drug Interaction Precaution". Read these warnings carefully.
Make a list of all your prescription medications and over-the-counter products, including drugs, vitamins, and supplements. Review this list with all healthcare providers and your pharmacist. 
If possible, use one pharmacy for all your prescription medications and over-the-counter products. This way your pharmacist has a record of all your prescription drugs and can advise you about drug interactions and side effects.