In the United States, a non-profit, non-governmental organization called the United States Pharmacopeia (USP) was established in 1820 to ensure that prescription and over-the-counter drugs approved for use in the United States meet quality standards in order to be placed on the National Formulary issued by the U.S. Food and Drug Administration (FDA).14

Among its many functions, the USP was tasked by the U.S. Congress to classify drugs so that Medicare Prescription Drug Benefit providers can include them in their annual formularies.

Worldwide, there are 34 other countries that maintain national pharmacopeias, as well as a European Union Pharmacopeia for EU countries that don’t maintain their own pharmacopeia. Other countries will typically rely on the International Pharmacopeia maintained by the WHO.15

For its part, the USP classifies drugs in a far broader way than the ACT system, categorizing a drug, firstly, on its therapeutic use; secondly, on its mechanism/mode of action; and, thirdly, on its formulary classification. Even with this streamlined system, there are still dozens of different drug classes and thousands of different sub-classes and sub-categories.

From the broadest perspective, the USP currently categorizes a drug or drug component under one of 49 different therapeutic classes:16

Analgesics, including opioids and non-opioids
Anesthetics
Antibacterials, including antibiotics
Anticonvulsants
Antidementia agents
Antidepressants
Antidotes and antitoxins
Antiemetics
Antifungals
Anti-inflammatory agents, including corticosteroids and nonsteroidal anti-inflammatory drugs (NSAIDs)
Antimigraine agents
Antimyasthenic agents
Antimycobacterials
Antineoplastics
Antiparasitics
Antiparkinson agents
Antipsychotics
Antivirals, including HIV antiretrovirals and direct-acting hepatitis C drugs
Anxiolytic (anti-anxiety) agents
Bipolar agents
Blood glucose regulators, including insulin and other diabetes medications
Blood products, including anticoagulants
Cardiovascular agents, including beta-blockers and ACE inhibitors
Central nervous system agents, including amphetamines
Dental and oral agents
Dermatological (skin) agents
Enzyme replacement agent
Gastrointestinal agents, including H2 blockers and proton pump inhibitors
Genitourinary (genital and urinary tract) agents
Hormonal agents (adrenal)
Hormonal agents (pituitary)
Hormonal agents (prostaglandins)
Hormonal agents (sex hormones), including estrogen, testosterone, and anabolic steroids
Hormonal agents (thyroid)
Hormone suppressant (adrenal)
Hormone suppressant (parathyroid)
Hormone suppressant (pituitary)
Hormone suppressant (sex hormones)
Hormone suppressant (thyroid)
Immunological agents, including vaccines and disease-modifying anti-rheumatic drugs (DMARDs)
Inflammatory bowel disease agents
Metabolic bone disease agents
Ophthalmic (eye) agents
Otic (ear) agents
Respiratory tract agents, including antihistamines and bronchodilators
Sedatives and hypnotics
Skeletal muscle relaxants
Therapeutic nutrients, minerals, and electrolytes

Source: verywellhealth.com