Topic Resources
Everyone responds to medications differently. The way a person responds to a medication is affected by many factors, including:
Age
Body size
Use of other medications and dietary supplements (such as medicinal herbs)
Consumption of food (including beverages)
Presence of diseases (such as kidney or liver disease)
Storage of the medication (whether the medication was stored too long or in the wrong environment)
Development of tolerance and resistance
Whether people take a medication as instructed (adherence) also affects their response to it. These factors may affect how the body absorbs the medication, how the body breaks down (metabolizes) and eliminates the medication, or what effects the medication has on the body.
Because so many factors affect medication response, doctors must choose a medication appropriate for each person and must adjust the dose carefully. This process is more complex if the person takes other medications and has other diseases, because drug-drug and drug-disease interactions are possible.
A standard or average dose is determined for every new medication. But the concept of an average dose can be like "one size fits all" in clothing—It may fit a range of people well enough, but it may fit almost no one perfectly. For some medications, however, the dose does not have to be adjusted, because the same dose works well in virtually everyone.
Effects of age on drug response
Infants and older adults particularly have problems with medication response. Their liver and kidneys function less effectively, so medications that are broken down by the liver or excreted by the kidneys tend to accumulate, thus potentially causing problems.
Older adults typically have more disorders than children and younger adults and thus usually take more medications (see Aging and Medications). The more medications people take, the more likely they are to have problems caused by one medication interfering with another medication or disease. With aging, people also may have more difficulty following complicated instructions for taking medications, such as to take the medication at very specific times or to avoid certain foods.
Many Factors Affect Medication Response
