When you take a medication, you expect it to give you benefit. For example, if you have a headache, you would want to take a headache medication, and you would expect then to have relief of your headache. Most individuals realize that this does not always happen. Not every medication works for everyone who takes it, and this it is completely normal. A medication that works for your neighbor may not work for you. The purpose of this book is to provide you with some insight as to why medicines do not always work. New drugs and other modalities are being introduced with increasing frequency. A patient needs to partner with his or her doctor and become involved in their pharmacologic treatment. The reason for this book is to give a patient the basic information necessary to rationally discuss his or her medication failure with the treating physician. A medication is a drug used to treat an illness. The drug that you take goes from outside your body to a specific area in your body called a target receptor. This is the area on your body here your medication is supposed to work (heart, lung, etc.). This drug-receptor action is dependent on your specific pharmacodynamics and kinetics. Pharmacodynamics is the science of how a drug works for your body. This is called the mechanism of action of the drug which determines how a drug gives you pain relief. Pharmacokinetics, on the other hand, is the study of how drugs enter your body; reach their site of action (your heart, brain, etc.), and how they are eliminated from your body. Drug absorption is a drug's progress from the time it's administered until it reaches your blood systemic circulation.Drug absorption occurs when drugs are taken into your body. Drugs must readily dissolve in fat to pass through the lining of your gastrointestinal tract. The stomach is highly acidic, which favors absorption of weakly acidic drugs. The small intestine is slightly alkaline, which favors the absorption of weakly basic drugs. The small intestine is the major site of drug absorption due to its large surface area. Bioavailability describes what proportion of the administered drug is available to produce a pharmacologic response. Some factors influencing drug bioavailability include how rapidly and completely the drug will dissolve and will be absorbed through your gastrointestinal tract. Factors influencing drug bioavailability are: the presence of food may affect the dissolution and absorption of drugs, excretion in your feces, a deficiency or absence of gastric hydrochloric acid, which prevents gastric absorption of acidic drugs and prevents dissolution of basic drugs. Drug distribution is also important for you to understand. Drug distribution means that the drug that you took ultimately has to go somewhere such as your brain heart, etc. It may go to many other areas before it gets to where you want it to go. In other words, it may go to many areas in your body. The purpose of this book is to explain to the reader that it is not unusual for a drug to occasionally not be effective. The purpose of this book is to attempt to alleviate the frustration experienced when a medication does not always work and attempts to explain why a medication will not work.