MSD Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Drug Errors


Shalini S. Lynch

, PharmD, University of California San Francisco School of Pharmacy

Reviewed/Revised May 2022 | Modified Sep 2022
Topic Resources

Drug errors are mistakes made by doctors, health care practitioners, pharmacists, and patients when drugs are prescribed, given, taken, or stored. Drug errors can make people ill and allow diseases to worsen. In the United States, drug errors are estimated to cost the health care system up to $177 billion (depending on definitions) every year. (See also Overview of Drugs Overview of Drugs A drug is defined by U.S. law as any substance (other than a food or device) intended for use in the diagnosis, cure, relief, treatment, or prevention of disease or intended to affect the structure... read more .)

Drug errors may be caused by the following:

  • People become confused and take drugs incorrectly.

  • Doctors choose the wrong drug or write a prescription for the wrong dose.

  • Pharmacists incorrectly read the prescription or the drug container and give the wrong drug or dose.

  • Caregivers incorrectly read the label of the drug container and give the wrong drug or dose.

  • Caregivers give a drug to the wrong person.

  • The pharmacist or person incorrectly stores the drug, weakening the drug’s strength.

  • People use an expired drug.

  • People take a drug with food when the drug is best absorbed on an empty stomach, or without food when food is needed to prevent side effects.

Drug errors most commonly result from people’s confusion about when and how to take drugs, causing them to take the wrong drug or dose. Common reasons for confusion include people putting more than one kind of medication in a single bottle, worn-off instructions on the medication bottle, not understanding the instructions on a medication bottle, having more than one bottle of the same medication, and having so many bottles of medications that people become unsure which one to take when (and which ones have already been taken).

Using medication organizers

Medication organizers can be helpful, particularly when people take several different medications a day. These organizers have separate compartments for each day of the week and up to 4 different times of day. People or their caregivers place a week's worth of medications in the appropriate compartment. For example, if a drug is prescribed to be taken once a day in the morning, they would place one dose in the "morning" compartment of each day. At the appropriate time of day, people take all the medications in that particular compartment. Because all medications in a compartment are taken at the same time, it does not matter that different medications are mixed together. In addition to being a reminder for people, these organizers let caregivers see whether people have taken their medications.

Understanding prescriptions

People should be sure they understand how and when to take a drug when they pick up a prescription. If they do not understand, they should ask their pharmacist to explain how to take their drugs.

Prescribing drugs

Doctors sometimes make errors when prescribing drugs, especially among certain groups of people. Older people, pregnant women, and children are particularly at risk because they typically require different drugs, different doses, or both. Other errors involve drug interactions Drug Interactions The effect a drug has on a person may be different than expected because that drug interacts with Another drug the person is taking (drug-drug interaction) Food, beverages, or supplements the... read more , in which one drug increases or decreases the effect of another drug.

Drug interactions are more likely to occur in people who take many drugs. To minimize this risk, doctors need to know all drugs their patients are taking—including those prescribed by other health care practitioners and over-the-counter drugs. People should keep a written list of all their current drugs and dosages and bring the list to every health care appointment or emergency department visit. If there is any doubt as to which drugs are being used, people are instructed to bring all their drugs to their health care appointments for review.

Dispensing and administering drugs

Drugs may be given incorrectly in institutions. A drug may be given to the wrong person, at the wrong time, or by the wrong route. For instance, a drug may be given by vein (intravenously) when it is supposed to be given by mouth. Certain drugs must be given slowly when given by vein, and some drugs cannot be given at the same time. Many institutions now have computerized pharmacy systems that dispense each dose of the person's drugs labeled with a bar code that is scanned and matched with the person's identification bracelet. Such systems may help decrease the incidence of drug errors.

Storing drugs properly

Pharmacists should store drugs in the proper manner. For example, many drugs must be kept away from heat, and some drugs must be refrigerated. Mail-order pharmacies must be careful that drugs do not get too hot during shipping. If people store drugs incorrectly at home, drugs are likely to decrease in strength long before the stated expiration date.

People should check the label to see whether a drug needs to be stored in the refrigerator or kept cool. On the other hand, unnecessary precautions may make it harder for people to take drugs as directed and waste people's time. For example, unopened insulin should be refrigerated, but an open bottle often can be stored safely outside the refrigerator. Additionally, if children do not have access to the drug, drugs can be stored in their original childproof containers with a non–childproof lid.

Taking expired drugs

People mistakenly use expired drugs. Expired drugs are often ineffective because the drugs deteriorate with time. However, some drugs (such as aspirin or tetracycline) deteriorate into toxic substances and can actually be harmful if used past the expiration date.

More Information

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

quiz link

Test your knowledge

Take a Quiz!