Many factors can increase the likelihood of an adverse drug reaction (any unwanted effects of a drug or medication). They include
Hereditary factors
Certain preexisting diseases
Very young or old age
Pregnancy
Breastfeeding
Hereditary factors make some people more susceptible to the toxic effects of certain drugs (including medications). Various genes have been identified that affect how the body responds to drugs. For example, differences in certain genes can affect metabolism of drugs in the liver, allowing drug levels to rise and increase the chances of an adverse drug reaction. However, testing for these differences is complex and is not yet used routinely in clinical practice.
Certain preexisting diseases can alter drug absorption, metabolism, and elimination and the body's response to drugs (see Drug Interactions: Drug-Disease Interactions), increasing the risk of adverse drug reactions.
How mind-body interactions, such as mental attitude, outlook, belief in self, and confidence in health care practitioners, influence adverse drug reactions remains largely unexplored.
Use of Several Drugs
Taking several medications, whether prescription or over-the-counter, contributes to the risk of having an adverse drug reaction (see Drug-Drug Interactions). The number and severity of adverse drug reactions increase disproportionately as the number of drugs taken increases. The use of alcohol, which is also a drug, also increases the risk. Asking a doctor or pharmacist to periodically review all the drugs a person is taking and to make appropriate adjustments can reduce the risk of an adverse drug reaction.
Age
Older people are at high risk of having an adverse drug reaction for several reasons (see Aging and Drugs). They are likely to have many health problems and thus to be taking several prescription and over-the-counter drugs. Also, as people age, the liver is less able to metabolize many drugs, and the kidneys are less able to eliminate drugs from the body, increasing the risk of kidney damage by a drug and other adverse drug reactions. These age-related problems are often made worse by undernourishment and dehydration, which tend to become more common as people age.
Older people are also more sensitive to the effects of many drugs. For example, older people are more likely to experience light-headedness, loss of appetite, depression, confusion, and impaired coordination, putting them at risk of falling and fracturing a bone. Medications that can cause these reactions include many antihistamines, sleep aids, antianxiety drugs, antihypertensives, and antidepressants (see table Some Drugs Particularly Likely to Cause Problems in Older People).
Pregnancy and Breastfeeding
Some Drugs That Can Cause Problems During Pregnancy). However, for some medications, including ACE inhibitors and ARBs, risk increases during the second and third trimesters of pregnancy. Use of any prescription medications, over-the-counter drugs, and dietary supplements (including medicinal herbs)
Medications and medicinal herbs may be transmitted through breast milk to an infant (see Drugs Use During Breastfeeding). Some drugs should not be taken by women who are breastfeeding, whereas others can be taken but require a doctor's supervision. Some drugs do not usually harm the breastfed infant. However, women who are breastfeeding should consult with a health care practitioner before they take any drugs. Social and illicit drugs may harm a breastfeeding infant.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
2019 American Geriatrics Society Beers Criteria® Update Expert Panel: American Geriatrics Society 2019 updated AGS Beers Criteria® for potentially inappropriate dedication use in older adults. J Am Geriatr Soc 2019, 67(4):674-694. doi: 10.1111/jgs.15767
American Association of Poison Control Centers: Access to information on a variety of poisons, an emergency helpline (1-800-222-1222), and tips on prevention.
FDA Adverse Event Reporting System (FAERS): Access to Questions and Answers on FDA's Adverse Event Reporting System (FAERS).
