Also called: Side effects
Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
A drug interaction is a change in the way a drug acts in the body when taken with certain other drugs, foods, or supplements or when taken while you have certain medical conditions. Examples include:
- Two drugs, such as aspirin and blood thinners
- Drugs and food, such as statins and grapefruit
- Drugs and supplements, such as gingko and blood thinners
- Drugs and medical conditions, such as aspirin and peptic ulcers
Interactions could cause a drug to be more or less effective, cause side effects, or change the way one or both drugs work.
Side effects are unwanted, usually unpleasant, effects caused by medicines. Most are mild, such as a stomachache, dry mouth, or drowsiness, and go away after you stop taking the medicine. Others can be more serious. Sometimes a drug can interact with a disease that you have and cause a side effect. For example, if you have a heart condition, certain decongestants can cause you to have a rapid heartbeat.
Drug allergies are another type of reaction. They can range from mild to life-threatening. Skin reactions, such as hives and rashes, are the most common type. Anaphylaxis, a serious allergic reaction, is less common.
When you start a new prescription or over-the-counter medicine, make sure you understand how to take it correctly. Know which other medicines, foods, and supplements you need to avoid. Always talk to your health care provider or pharmacist if you have questions about your medicines.
It sits within Drug Therapy.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Drug Reactions
1,205 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- Minimising Adverse Drug Reactions and Verifying Economic Legitimacy in Children (MARVEL-PIC)Murdoch Childrens Research Institute
- Real World Asparaginase Therapy ToxicitySt. Jude Children's Research Hospital
- Drug-induced Liver Injury: Itching StudyUniversity of Nottingham
- The CARDIOPROTECT TrialBeth Israel Deaconess Medical Center
- A Computer-Assisted Tool for Objective Assessment of Extrapyramidal SymptomsShanghai Mental Health Center
- A Study to Evaluate LY3537021 for the Treatment of Nausea and Vomiting Caused by Chemotherapy in Adults With CancerEli Lilly and Company
Research already completed
- 05-001: Treatment of Acute Lymphoblastic Leukemia in ChildrenDana-Farber Cancer Institute
- SPI-1005 for Prevention and Treatment of Tobramycin Induced OtotoxicitySound Pharmaceuticals, Incorporated
- Discrimination of DILI and AIH by Artificial IntelligenceBeijing Friendship Hospital
- ANTthracycline-induced Inflammation and OXidative Stress: 10-year Follow-upUniversity of Chile
- Safety of Pediatric COVID-19 VaccinationDuke University
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Start Here
- Drug AllergyMayo Foundation for Medical Education and Research
- Drug Interactions: What You Should KnowFood and Drug Administration
- Medications and Drug Allergic ReactionsAmerican Academy of Allergy, Asthma, and Immunology
Learn More
- Drug Allergies: What to Look Out ForNational Institutes of Health
- Medication/Drug AllergyNational Jewish Health
Diagnosis and Tests
- Allergy Skin TestNational Library of Medicine
- AnaphylaxisAmerican Academy of Allergy, Asthma, and Immunology
- Anaphylaxis-Like ReactionsNational Jewish Health
- Pharmacogenetic TestsNational Library of Medicine
- Pharmacogenetics: How Genetic Testing Can Guide Medicine DecisionsNemours Foundation
- Therapeutic Drug MonitoringNational Library of Medicine
Treatments and Therapies
- Anaphylaxis: First AidMayo Foundation for Medical Education and Research
Related Issues
- Drug-Food InteractionsAmerican Academy of Family Physicians
- FDA Pharmacists Help You Use Medicines SafelyFood and Drug Administration
- Harmful Interactions: Mixing Alcohol with MedicinesNational Institute on Alcohol Abuse and Alcoholism
- Know the Science: How Medications and Supplements Can InteractNational Center for Complementary and Integrative Health
- Medication Interactions: Food, Supplements, and Other DrugsAmerican Heart Association
- MedWatch: The FDA Safety Information and Adverse Event Reporting ProgramFood and Drug Administration
Genetics
- Stevens-Johnson syndrome/toxic epidermal necrolysis: MedlinePlus GeneticsNational Library of Medicine
- Thiopurine S-methyltransferase deficiency: MedlinePlus GeneticsNational Library of Medicine
Clinical Trials
- ClinicalTrials.gov: Drug HypersensitivityNational Institutes of Health
- ClinicalTrials.gov: Drug InteractionsNational Institutes of Health
- ClinicalTrials.gov: Drug-Related Side Effects and Adverse ReactionsNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Drug-Related Side Effects and Adverse Reactions, Drug Hypersensitivity, Metabolic Side Effects of Drugs and Substances, Chemical and Drug Induced Liver Injury, Drug Interactions. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Drug Reactions, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.