Table of ContentsView AllTable of ContentsTypesPurposeATC ClassificationUSP Classification
Table of ContentsView All
View All
Table of Contents
Types
Purpose
ATC Classification
USP Classification
A drug class is a group of medications with similar properties. The three main methodologies used to classify drugs according to the Food and Drug Administration (FDA) include:
This article explains how medication classifications work, why they are necessary, and how one drug can be classified in several different ways. It also describes different classification systems and their distinct purposes.
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Multiple Categories of Classification
Not all drugs fit neatly into a single category. Some drugs are grouped together under one classification method but not another. Some have multiple classifications.
One Drug, Different Physiological Effects
Many drugs have multiple uses and, as such, multiple classifications. For example,Lyrica (pregabalin)and Trileptal (oxcarbazepine) are both classified asanticonvulsantsand can be used to treatepilepsy.
At the same time, Lyrica can be classified as ananalgesicand used to treat chronic nerve pain alongside antidepressant drugs likeCymbalta (duloxetine).Lyrica may also be used as ananxiolyticto treatsocial anxiety disorder (SAD)alongside antidepressants like Paxil (paroxetine).
Another example isfinasteride, which is commonly used to treatenlarged prostate(under the brand name Proscar) and regrow hair (under the brand name Propecia). Though classified differently, the two drugs only differ in their doses (5 milligrams for Proscar and 1 milligram for Propecia).
One Physiological Effect, Different Classifications
One drug can be classified in several different ways based on its mechanism of action, physiological effects, and chemical structure.
In terms of chemical structure, ACE inhibitors are so-named because they have a distinct molecular structure that directly inhibits (blocks) an enzyme called angiotensin-converting enzyme (ACE) that causes blood vessels to narrow and blood pressure to increase.
Purpose of Drug Classification
Drugs are classified to ensure that a drug is used safely and that you get the greatest possible benefit with the lowest possible risk.
The various drug classifications help to:
Avoiding Interactions
The action of one drug can make another drug less effective.
Taking these drugs together lowers the amount of protease inhibitors in the bloodstream (referred to as their bioavailability), making them less effective.
Avoiding “Drug Competition”
Although many of these drugs belong to different classes, taking them together can force the drugs to “compete” for the available CYP450 in the bloodstream.
As a result, the concentration of one drug may go up because it is not being broken down sufficiently (increasing the risk of side effects), while the concentration of the other may go down as it is eliminated from the body too quickly (making it less effective).
By identifying these interactions, healthcare providers can separate doses, increase the dose, or change treatment to avoid this effect.
Preventing Toxicity
Toxicity, sometimes referred to as drug poisoning, can occur if you overdose on a drug or have health problems like liver disease or kidney disease that prevent the normal elimination of a drug from the body.
This same enzyme is also responsible for the production of a blood-clotting chemical called thromboxane A2. By suppressing COX, blood clots less effectively, leading to possible side effects like easy bruising, nosebleeds, and stomach ulcers.
Taking Advil and Aleve can amplify this effect and even lead to internal bleeding andkidney failureif used in excess.
Many other drug classes have this accumulative effect, including antidepressants known asSSRIs and SNRIsthat affect levels ofserotoninin the brain. Taking more than one serotonin-related medication increases your risk ofserotonin syndrome, a potentially serious drug reaction that can lead to seizures, abnormal heart rhythms, and even death.
Assessing Drug Resistance
Medications used to treat chronic infections have the potential for drug resistance. This occurs when a virus or bacteria mutates and is able to escape the effects of an antiviral or antibiotic drug.
Resistance can occur naturally over time as minor mutations suddenly become major mutations or when you don’t take a drug as prescribed, allowing a germ to mutate freely. When resistance develops, a drug may be far less effective or not work at all.
To make matters worse, resistance to one drug often confers resistance to every other drug in the class.
Some drugs and drug classes are more vulnerable to resistance than others. By understanding which are and which are not, healthcare providers can “stage” treatment to ensure the first-line drugs last longer and are less likely to develop resistance if you miss a dose.
This is why a newer class of HIV drug calledintegrase inhibitorsis used in first-line therapy in favor of older drugs like non-nucleoside reverse transcriptase inhibitors (NNRTIs) that can develop resistance within the span of three years.
The same applies to antibiotics. The overuse of antibiotics has led to increasing patterns ofantibiotic resistanceworldwide. Identifying these patterns ensures the correct drug is prescribed to effectively clear the infection and prevent the spread of drug-resistant bacteria.
For diseases likegonorrhea, the resistance to available antibiotics has become so severe that the Centers for Disease Control and Prevention (CDC) recommend only treatment for it: a single dose ofceftriaxone.Resistance to other classes of antibiotics—including penicillins, sulphonamides, tetracyclines, quinolones, and macrolides—is so deep that they are not considered effective.
Determining Dosage and Risk of Dependence
Every drug has abiological half-life, meaning the time it takes for 50% of the drug to leave your system. The shorter a drug’s half-life is, the more you have to take to keep the drug concentration in your blood at a therapeutic level.
This is why some drugs need to be taken three to four times a day, while others may only be needed daily, weekly, or monthly.
The problem with a short half-life is that a drug is far less “forgiving,” meaning that you are less likely to achieve the intended result if you miss a dose. Drugs with long half-lives are generally more forgiving because they can remain at a therapeutic level even if you miss a dose.
Another problem with a short half-life is that you can develop drug dependence (also known as addiction). This is because your body “needs” the drug frequently to achieve the desired effect, and can cause withdrawal symptoms if it doesn’t get it. This is especially true with drugs that act on thecentral nervous system.
A prime example of this isfentanyl, an opioid drug painkiller. The combination of a short drug half-life (six to nine hours) and a potent physiological effect can create the perfect storm for drug dependence, often within a couple of weeks.
ATC Classification System
The thousands of drug classes and subclasses can be classified in several ways.
This system is meant for healthcare providers and isn’t useful to patients. But the strict hierarchy it establishes protects people from drug errors (like getting the wrong one.)
USP Drug Classification
A non-profit, non-governmental organization called the United States Pharmacopeia (USP) was established in 1820. Its goal is to ensure prescription and OTC drugs approved in the U.S. meet quality standards.
From the broadest perspective, you’re left with 47 drug categories and more than a hundred classes within those categories.
AnalgesicsAntipsychoticsHormonal agents (pituitary)AnestheticsAntispasticity agentsHormonal agents (prostaglandins)Anti-addiction agentsAntiviralsHormonal agents (sex hormones)AntibacterialsAnxiolyticsHormonal agents (thyroid)AnticonvulsantsBipolar agentsHormone suppressant (adrenal)Antidementia agentsBlood glucose regulatorsHormone suppressant (pituitary)AntidepressantsBlood productsHormone suppressant (thyroid)AntiemeticsCardiovascular agentsImmunological agentsAntifungalsCentral nervous system agentsInflammatory bowel disease agentsAntigout agentsDental and oral agentsMetabolic bone disease agentsAntimigraine agentsDermatological agentsOphthalmic agentsAntimyasthenic agentsElectrolytes, minerals, metals, vitaminsOtic agentsAntimycobacterialsGastrointestinal agentsRespiratory tract agentsAntineoplasticsGenetic/enzyme/protein disorder agentsSkeletal muscle relaxantsAntiparasiticsGenitourinary agentsSleep disorder agentsAntiparkinson agentsHormonal agents (adrenal)SummaryDrug classifications are important. They help protect you from severe side effects and drug interactions; ensure your body can break down and use the medication; and help guide many treatment decisions.The main classification systems are ATC and USP. They use different methods but both are useful tools.Tips for Taking Medication Safely
Summary
Drug classifications are important. They help protect you from severe side effects and drug interactions; ensure your body can break down and use the medication; and help guide many treatment decisions.
The main classification systems are ATC and USP. They use different methods but both are useful tools.
Tips for Taking Medication Safely
20 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.Food and Drug Administration.Pharmacologic class.Sills GJ, Rogawski MA.Mechanisms of action of currently used antiseizure drugs.Neuropharmacology. 2020;168:107966. doi:10.1016/j.neuropharm.2020.107966Derry S, Cording M, Wiffen PJ, Law S, Phillips T, Moore RA.Pregabalin for pain in fibromyalgia in adults.Cochrane Database Syst Rev.2016;9:CD011790. doi:10.1002/14651858.CD011790.pub2Kawalec P, Cierniak A, Pilc A, Nowak G.Pregabalin for the treatment of social anxiety disorder.Expert Opin Investig Drugs.2015;24(4):585-94. doi:10.1517/13543784.2014.979283National Library of Medicine: MedlinePlus.Finasteride.Food and Drug Administration.Angiotensin-converting enzyme inhibitor (ACE inhibitor) drugs,Lewis JM, Stott KE, Monnery D, et al.Managing potential drug-drug interactions between gastric acid-reducing agents and antiretroviral therapy: experience from a large HIV-positive cohort.Int J STD AIDS. 2016;27(2):105-109. doi:10.1177/0956462415574632Zhao M, Ma J, Li M. et al.Cytochrome P450 enzymes and drug metabolism in humans.Int J Mol Sci.2021;22(23):12808. doi:10.3390/ijms222312808Sohail R, Mathew M, Patel K K, et al.Effects of non-steroidal anti-inflammatory drugs (NSAIDs) and gastroprotective NSAIDs on the gastrointestinal tract: a narrative review.Cureus. 2023:15(4):e37080. doi:10.7759/cureus.37080Royal Children’s Hospital.Nonsteroidal anti-inflammatory drug NSAID poisoning.Scotton WJ, Hill LJ, Williams AC, Barnes NM.Serotonin syndrome: pathophysiology, clinical features, management, and potential future directions.Int J Tryptophan Res.2019;12:1178646919873925. doi:10.1177/1178646919873925HHS Panel on Antiretroviral Guidelines for Adults and Adolescents.Guidelines for the use of antiretroviral agents in adults and adolescents with HIV.Centers for Disease Control and Prevention.Sexually transmitted infections treatment guidelines, 2021. Gonococcal infections among adolescents and adults.World Health Organization.Multi-drug resistant gonorrhoea.Lerner A, Klein M.Dependence, withdrawal and rebound of CNS drugs: an update and regulatory considerations for new drugs development,Brain Commun.2019;1(1):fcz025. doi:10.1093/braincomms/fcz025Kharasch ED.Opioid half-lives and hemlines: the long and short of fashion.Anesthesiology.2015;122(5):969–970. doi:10.1097/ALN.0000000000000634WHO Collaborating Centre for Drug Statistics Methodology.History.World Health Organization Collaborating Centre for Drug Statistics Methodology.Guidelines for ATC classification and DDD assignment.United States Pharmacopeial Convention.USP and CMS working together for quality and safety of healthcare.World Health Organization.Index of national, regional and international pharmacopoeias.Additional ReadingUnited States Pharmacopeial Convention.USP drug classification.
20 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.Food and Drug Administration.Pharmacologic class.Sills GJ, Rogawski MA.Mechanisms of action of currently used antiseizure drugs.Neuropharmacology. 2020;168:107966. doi:10.1016/j.neuropharm.2020.107966Derry S, Cording M, Wiffen PJ, Law S, Phillips T, Moore RA.Pregabalin for pain in fibromyalgia in adults.Cochrane Database Syst Rev.2016;9:CD011790. doi:10.1002/14651858.CD011790.pub2Kawalec P, Cierniak A, Pilc A, Nowak G.Pregabalin for the treatment of social anxiety disorder.Expert Opin Investig Drugs.2015;24(4):585-94. doi:10.1517/13543784.2014.979283National Library of Medicine: MedlinePlus.Finasteride.Food and Drug Administration.Angiotensin-converting enzyme inhibitor (ACE inhibitor) drugs,Lewis JM, Stott KE, Monnery D, et al.Managing potential drug-drug interactions between gastric acid-reducing agents and antiretroviral therapy: experience from a large HIV-positive cohort.Int J STD AIDS. 2016;27(2):105-109. doi:10.1177/0956462415574632Zhao M, Ma J, Li M. et al.Cytochrome P450 enzymes and drug metabolism in humans.Int J Mol Sci.2021;22(23):12808. doi:10.3390/ijms222312808Sohail R, Mathew M, Patel K K, et al.Effects of non-steroidal anti-inflammatory drugs (NSAIDs) and gastroprotective NSAIDs on the gastrointestinal tract: a narrative review.Cureus. 2023:15(4):e37080. doi:10.7759/cureus.37080Royal Children’s Hospital.Nonsteroidal anti-inflammatory drug NSAID poisoning.Scotton WJ, Hill LJ, Williams AC, Barnes NM.Serotonin syndrome: pathophysiology, clinical features, management, and potential future directions.Int J Tryptophan Res.2019;12:1178646919873925. doi:10.1177/1178646919873925HHS Panel on Antiretroviral Guidelines for Adults and Adolescents.Guidelines for the use of antiretroviral agents in adults and adolescents with HIV.Centers for Disease Control and Prevention.Sexually transmitted infections treatment guidelines, 2021. Gonococcal infections among adolescents and adults.World Health Organization.Multi-drug resistant gonorrhoea.Lerner A, Klein M.Dependence, withdrawal and rebound of CNS drugs: an update and regulatory considerations for new drugs development,Brain Commun.2019;1(1):fcz025. doi:10.1093/braincomms/fcz025Kharasch ED.Opioid half-lives and hemlines: the long and short of fashion.Anesthesiology.2015;122(5):969–970. doi:10.1097/ALN.0000000000000634WHO Collaborating Centre for Drug Statistics Methodology.History.World Health Organization Collaborating Centre for Drug Statistics Methodology.Guidelines for ATC classification and DDD assignment.United States Pharmacopeial Convention.USP and CMS working together for quality and safety of healthcare.World Health Organization.Index of national, regional and international pharmacopoeias.Additional ReadingUnited States Pharmacopeial Convention.USP drug classification.
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.
Food and Drug Administration.Pharmacologic class.Sills GJ, Rogawski MA.Mechanisms of action of currently used antiseizure drugs.Neuropharmacology. 2020;168:107966. doi:10.1016/j.neuropharm.2020.107966Derry S, Cording M, Wiffen PJ, Law S, Phillips T, Moore RA.Pregabalin for pain in fibromyalgia in adults.Cochrane Database Syst Rev.2016;9:CD011790. doi:10.1002/14651858.CD011790.pub2Kawalec P, Cierniak A, Pilc A, Nowak G.Pregabalin for the treatment of social anxiety disorder.Expert Opin Investig Drugs.2015;24(4):585-94. doi:10.1517/13543784.2014.979283National Library of Medicine: MedlinePlus.Finasteride.Food and Drug Administration.Angiotensin-converting enzyme inhibitor (ACE inhibitor) drugs,Lewis JM, Stott KE, Monnery D, et al.Managing potential drug-drug interactions between gastric acid-reducing agents and antiretroviral therapy: experience from a large HIV-positive cohort.Int J STD AIDS. 2016;27(2):105-109. doi:10.1177/0956462415574632Zhao M, Ma J, Li M. et al.Cytochrome P450 enzymes and drug metabolism in humans.Int J Mol Sci.2021;22(23):12808. doi:10.3390/ijms222312808Sohail R, Mathew M, Patel K K, et al.Effects of non-steroidal anti-inflammatory drugs (NSAIDs) and gastroprotective NSAIDs on the gastrointestinal tract: a narrative review.Cureus. 2023:15(4):e37080. doi:10.7759/cureus.37080Royal Children’s Hospital.Nonsteroidal anti-inflammatory drug NSAID poisoning.Scotton WJ, Hill LJ, Williams AC, Barnes NM.Serotonin syndrome: pathophysiology, clinical features, management, and potential future directions.Int J Tryptophan Res.2019;12:1178646919873925. doi:10.1177/1178646919873925HHS Panel on Antiretroviral Guidelines for Adults and Adolescents.Guidelines for the use of antiretroviral agents in adults and adolescents with HIV.Centers for Disease Control and Prevention.Sexually transmitted infections treatment guidelines, 2021. Gonococcal infections among adolescents and adults.World Health Organization.Multi-drug resistant gonorrhoea.Lerner A, Klein M.Dependence, withdrawal and rebound of CNS drugs: an update and regulatory considerations for new drugs development,Brain Commun.2019;1(1):fcz025. doi:10.1093/braincomms/fcz025Kharasch ED.Opioid half-lives and hemlines: the long and short of fashion.Anesthesiology.2015;122(5):969–970. doi:10.1097/ALN.0000000000000634WHO Collaborating Centre for Drug Statistics Methodology.History.World Health Organization Collaborating Centre for Drug Statistics Methodology.Guidelines for ATC classification and DDD assignment.United States Pharmacopeial Convention.USP and CMS working together for quality and safety of healthcare.World Health Organization.Index of national, regional and international pharmacopoeias.
Food and Drug Administration.Pharmacologic class.
Sills GJ, Rogawski MA.Mechanisms of action of currently used antiseizure drugs.Neuropharmacology. 2020;168:107966. doi:10.1016/j.neuropharm.2020.107966
Derry S, Cording M, Wiffen PJ, Law S, Phillips T, Moore RA.Pregabalin for pain in fibromyalgia in adults.Cochrane Database Syst Rev.2016;9:CD011790. doi:10.1002/14651858.CD011790.pub2
Kawalec P, Cierniak A, Pilc A, Nowak G.Pregabalin for the treatment of social anxiety disorder.Expert Opin Investig Drugs.2015;24(4):585-94. doi:10.1517/13543784.2014.979283
National Library of Medicine: MedlinePlus.Finasteride.
Food and Drug Administration.Angiotensin-converting enzyme inhibitor (ACE inhibitor) drugs,
Lewis JM, Stott KE, Monnery D, et al.Managing potential drug-drug interactions between gastric acid-reducing agents and antiretroviral therapy: experience from a large HIV-positive cohort.Int J STD AIDS. 2016;27(2):105-109. doi:10.1177/0956462415574632
Zhao M, Ma J, Li M. et al.Cytochrome P450 enzymes and drug metabolism in humans.Int J Mol Sci.2021;22(23):12808. doi:10.3390/ijms222312808
Sohail R, Mathew M, Patel K K, et al.Effects of non-steroidal anti-inflammatory drugs (NSAIDs) and gastroprotective NSAIDs on the gastrointestinal tract: a narrative review.Cureus. 2023:15(4):e37080. doi:10.7759/cureus.37080
Royal Children’s Hospital.Nonsteroidal anti-inflammatory drug NSAID poisoning.
Scotton WJ, Hill LJ, Williams AC, Barnes NM.Serotonin syndrome: pathophysiology, clinical features, management, and potential future directions.Int J Tryptophan Res.2019;12:1178646919873925. doi:10.1177/1178646919873925
HHS Panel on Antiretroviral Guidelines for Adults and Adolescents.Guidelines for the use of antiretroviral agents in adults and adolescents with HIV.
Centers for Disease Control and Prevention.Sexually transmitted infections treatment guidelines, 2021. Gonococcal infections among adolescents and adults.
World Health Organization.Multi-drug resistant gonorrhoea.
Lerner A, Klein M.Dependence, withdrawal and rebound of CNS drugs: an update and regulatory considerations for new drugs development,Brain Commun.2019;1(1):fcz025. doi:10.1093/braincomms/fcz025
Kharasch ED.Opioid half-lives and hemlines: the long and short of fashion.Anesthesiology.2015;122(5):969–970. doi:10.1097/ALN.0000000000000634
WHO Collaborating Centre for Drug Statistics Methodology.History.
World Health Organization Collaborating Centre for Drug Statistics Methodology.Guidelines for ATC classification and DDD assignment.
United States Pharmacopeial Convention.USP and CMS working together for quality and safety of healthcare.
World Health Organization.Index of national, regional and international pharmacopoeias.
United States Pharmacopeial Convention.USP drug classification.
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