Table of ContentsView AllTable of ContentsTypesSignsvs. Side Effectsvs. Adverse Effectsvs. Allergyvs. Adverse EventsWhen to See a Provider
Table of ContentsView All
View All
Table of Contents
Types
Signs
vs. Side Effects
vs. Adverse Effects
vs. Allergy
vs. Adverse Events
When to See a Provider
An adverse reaction is an undesirable reaction to a medication that’s been taken correctly. It may occur immediately, hours, or years after starting a drug. Reactions might include minor side effects like mildheartburnor life-threatening issues such asheart failure.
Any prescription or over-the-counter (OTC) medication, supplement, or herbal product could potentially cause a problem. If you suspect you’re having a drug reaction, talk to your healthcare provider. You may be able to manage the symptoms or be advised to taper off the drug slowly rather than stop it cold.
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Types of Adverse Reactions
Reactions may bedose-dependent, which means the side effects can be predicted and increase along with an increase in the dose of a drug. An example would be a medication that causes fatigue, in which tiredness worsens when a higher dose is taken.
Anidiosyncratic reactionis not predictable based on the drug’s composition. An example would be a medication that causes diarrhea for a patient when it ordinarily would cause constipation.
Classifying Adverse Reactions
Several different systems are used to identify the type of adverse reaction that might occur when taking a medication. One of the most common and detailed is the Wills and Brown classification, which divides adverse reactions according to the drug’s mechanism, meaning how it affects the body.
Who’s at Risk for Adverse Drug Reactions?People over 65 are most at risk of adverse reactions to medication. They’re hospitalized due to these reactions at twice the rate of younger people.
Who’s at Risk for Adverse Drug Reactions?
People over 65 are most at risk of adverse reactions to medication. They’re hospitalized due to these reactions at twice the rate of younger people.
Signs of an Adverse Reaction
Adverse reactions may occur at any time after starting a drug, from an immediate reaction to effects that do not appear for years.
Mild adverse drug reactions might include:
Moderate adverse drug reactions might include:
Severe adverse drug reactions are rare but can include life-threatening issues such as:
Warnings About Illness and DeathIt is estimated that more than two million people in the United States have serious adverse drug reactions each year. Adverse reactions cause about 100,000 deaths annually.Your healthcare provider should discuss any potential serious reactions with you before you begin taking the medication.
Warnings About Illness and Death
It is estimated that more than two million people in the United States have serious adverse drug reactions each year. Adverse reactions cause about 100,000 deaths annually.Your healthcare provider should discuss any potential serious reactions with you before you begin taking the medication.
It is estimated that more than two million people in the United States have serious adverse drug reactions each year. Adverse reactions cause about 100,000 deaths annually.
Your healthcare provider should discuss any potential serious reactions with you before you begin taking the medication.
Adverse Reaction vs. Side Effects
Whileadverse reactionis sometimes used interchangeably withside effects, the terms have slightly different meanings:
For example, some medications that cause fatigue as a side effect may be a problem for some people but could be used as a sleep aid for others.
Side Effects Can Be GoodIt’s important to note that sometimes a medication should be continued even if you have an adverse reaction. An example would be the medication Tarceva (erlotinib) used for lung cancer.This drug often causes an acne type of rash. However, the rash seems to indicate the drug is working well. In fact, the more severe the rash, the better the drug’s effect.In these situations, you and your healthcare provider should weigh the benefit of the treatment against the adverse reaction from the drug.
Side Effects Can Be Good
It’s important to note that sometimes a medication should be continued even if you have an adverse reaction. An example would be the medication Tarceva (erlotinib) used for lung cancer.This drug often causes an acne type of rash. However, the rash seems to indicate the drug is working well. In fact, the more severe the rash, the better the drug’s effect.In these situations, you and your healthcare provider should weigh the benefit of the treatment against the adverse reaction from the drug.
It’s important to note that sometimes a medication should be continued even if you have an adverse reaction. An example would be the medication Tarceva (erlotinib) used for lung cancer.
This drug often causes an acne type of rash. However, the rash seems to indicate the drug is working well. In fact, the more severe the rash, the better the drug’s effect.
In these situations, you and your healthcare provider should weigh the benefit of the treatment against the adverse reaction from the drug.
Adverse Reaction vs. Adverse Effects
Another term you may hear isadverse effects. This refers to something seen on lab tests or imaging studies. It’s different from an adverse reaction, which refers to clinical signs and symptoms experienced when taking a medication.
For example, your blood work may show that a drug caused your blood sugar to drop. This is an adverse effect. In relation to this, you may develop symptoms of hypoglycemia—that is the adverse reaction.
Adverse Reaction vs. Allergy
Adrug allergyis a serious matter. Technically, it’s a type of adverse reaction.
In an allergic reaction, your body recognizes the drug as foreign, mistakenly considers it dangerous, and activates the immune system to “fight it off.” The immune response is what causes allergy symptoms such as:
Trueallergic reactions to drugsmake up 5% to 10% of adverse reactions.
How to Reduce Your Risk of Allergies and Adverse ReactionsDiscuss all potential allergies and known side effects with your doctor before you take prescription or OTC medication.Check the information included with the medication for common drug reactions, allergens, and interactions.Search theFDALabel databaseto check for specific adverse reactions.
How to Reduce Your Risk of Allergies and Adverse Reactions
Discuss all potential allergies and known side effects with your doctor before you take prescription or OTC medication.Check the information included with the medication for common drug reactions, allergens, and interactions.Search theFDALabel databaseto check for specific adverse reactions.
Adverse Reactions vs. Adverse Events
Anadverse eventis a negative medical event that occurs while you’re taking a medication, but the reaction may not be related to the medication.
For instance, a medical study may note that one participant had a heart attack while taking a drug. That doesn’t necessarily mean that the drug caused it—it may have contributed, but it may also have just been a coincidence.
When to See a Healthcare Provider
If you suspect you are having an adverse reaction to a medication or treatment, it is important to let your healthcare provider know as soon as possible.
Depending on the severity, call 911, or make an appointment with a healthcare provider.
Bring all medications, including any vitamins, over-the-counter medications, and nutritional supplements to your appointment.
When you meet with your provider, they will likely ask about the following:
Summary
Discuss the risks and benefits with your healthcare provider, and if you notice unexpected reactions after taking a medication, contact your healthcare provider or 911 right away.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Angeline, A., and P. Perumaloo.From evolution to prevention of adverse drug reaction.Int J Pharm Pract5 (2015): 1170-1177.Lavan AH, Gallagher P.Predicting risk of adverse drug reactions in older adults.Ther Adv Drug Saf. 2016;7(1):11-22. doi:10.1177/2042098615615472Alomar MJ.Factors affecting the development of adverse drug reactions (Review article).Saudi Pharm J. 2014;22(2):83-94. doi:10.1016/j.jsps.2013.02.003Merck Manual.Severity of Adverse Drug Reactions.Bone A, Houck K.Adverse Drug Reactions: The benefits of data mining.eLife. 2017;6:e30280. doi:10.7554/eLife.30280National Cancer Institute.Definition of Side Effect.Owczarczyk-Saczonek A, Witmanowski H, Placek W.Acneiform rash during lung cancer therapy with erlotinib (Tarceva(®).Postepy Dermatol Alergol. 2013;30(3):195-198. doi:10.5114/pdia.2013.35624Centers for Disease Control and Prevention.Adverse Drug Events from Specific Medicines.American Collage of Allergy, Asthma, & Immunology.Drug allergies.American Academy of Allergy, Asthma and Immunology.Medications and Drug Allergic Reactions.Additional ReadingSundaran S, Udayana A, Hareendranath, K, et al.Study on the classification, causality, preventability and severity of adverse drug reaction using spontaneous reporting system in hospitalized patients.Pharmacy (Basel). 2018;6(4):108. Published 2018 Sep 29. doi:10.3390/pharmacy6040108
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Angeline, A., and P. Perumaloo.From evolution to prevention of adverse drug reaction.Int J Pharm Pract5 (2015): 1170-1177.Lavan AH, Gallagher P.Predicting risk of adverse drug reactions in older adults.Ther Adv Drug Saf. 2016;7(1):11-22. doi:10.1177/2042098615615472Alomar MJ.Factors affecting the development of adverse drug reactions (Review article).Saudi Pharm J. 2014;22(2):83-94. doi:10.1016/j.jsps.2013.02.003Merck Manual.Severity of Adverse Drug Reactions.Bone A, Houck K.Adverse Drug Reactions: The benefits of data mining.eLife. 2017;6:e30280. doi:10.7554/eLife.30280National Cancer Institute.Definition of Side Effect.Owczarczyk-Saczonek A, Witmanowski H, Placek W.Acneiform rash during lung cancer therapy with erlotinib (Tarceva(®).Postepy Dermatol Alergol. 2013;30(3):195-198. doi:10.5114/pdia.2013.35624Centers for Disease Control and Prevention.Adverse Drug Events from Specific Medicines.American Collage of Allergy, Asthma, & Immunology.Drug allergies.American Academy of Allergy, Asthma and Immunology.Medications and Drug Allergic Reactions.Additional ReadingSundaran S, Udayana A, Hareendranath, K, et al.Study on the classification, causality, preventability and severity of adverse drug reaction using spontaneous reporting system in hospitalized patients.Pharmacy (Basel). 2018;6(4):108. Published 2018 Sep 29. doi:10.3390/pharmacy6040108
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Angeline, A., and P. Perumaloo.From evolution to prevention of adverse drug reaction.Int J Pharm Pract5 (2015): 1170-1177.Lavan AH, Gallagher P.Predicting risk of adverse drug reactions in older adults.Ther Adv Drug Saf. 2016;7(1):11-22. doi:10.1177/2042098615615472Alomar MJ.Factors affecting the development of adverse drug reactions (Review article).Saudi Pharm J. 2014;22(2):83-94. doi:10.1016/j.jsps.2013.02.003Merck Manual.Severity of Adverse Drug Reactions.Bone A, Houck K.Adverse Drug Reactions: The benefits of data mining.eLife. 2017;6:e30280. doi:10.7554/eLife.30280National Cancer Institute.Definition of Side Effect.Owczarczyk-Saczonek A, Witmanowski H, Placek W.Acneiform rash during lung cancer therapy with erlotinib (Tarceva(®).Postepy Dermatol Alergol. 2013;30(3):195-198. doi:10.5114/pdia.2013.35624Centers for Disease Control and Prevention.Adverse Drug Events from Specific Medicines.American Collage of Allergy, Asthma, & Immunology.Drug allergies.American Academy of Allergy, Asthma and Immunology.Medications and Drug Allergic Reactions.
Angeline, A., and P. Perumaloo.From evolution to prevention of adverse drug reaction.Int J Pharm Pract5 (2015): 1170-1177.
Lavan AH, Gallagher P.Predicting risk of adverse drug reactions in older adults.Ther Adv Drug Saf. 2016;7(1):11-22. doi:10.1177/2042098615615472
Alomar MJ.Factors affecting the development of adverse drug reactions (Review article).Saudi Pharm J. 2014;22(2):83-94. doi:10.1016/j.jsps.2013.02.003
Merck Manual.Severity of Adverse Drug Reactions.
Bone A, Houck K.Adverse Drug Reactions: The benefits of data mining.eLife. 2017;6:e30280. doi:10.7554/eLife.30280
National Cancer Institute.Definition of Side Effect.
Owczarczyk-Saczonek A, Witmanowski H, Placek W.Acneiform rash during lung cancer therapy with erlotinib (Tarceva(®).Postepy Dermatol Alergol. 2013;30(3):195-198. doi:10.5114/pdia.2013.35624
Centers for Disease Control and Prevention.Adverse Drug Events from Specific Medicines.
American Collage of Allergy, Asthma, & Immunology.Drug allergies.
American Academy of Allergy, Asthma and Immunology.Medications and Drug Allergic Reactions.
Sundaran S, Udayana A, Hareendranath, K, et al.Study on the classification, causality, preventability and severity of adverse drug reaction using spontaneous reporting system in hospitalized patients.Pharmacy (Basel). 2018;6(4):108. Published 2018 Sep 29. doi:10.3390/pharmacy6040108
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