Drugs are classified according to a number of different criteria, depending on the group doing the classifying and the reason for classification.
For instance, from a therapeutic standpoint, a drug might be classified by the way it is used to treat illness. Other classification systems might classify drugs by active ingredients or chemical composition.
The Federal Food, Drug, and Cosmetic Act
Early on, the government developed a very basic classification system for medicines and offered a general classification system for drugs sold commercially for medicinal purposes. The Federal Food, Drug, and Cosmetic Act (FFDCA) was passed in 1938 to assist in deciding what drugs would be approved for specific uses. The FFDCA gave the Food and Drug Administration (FDA) the power to determine the safety of various food products, medicinal drugs, and cosmetics in the United States. The Act has been amended several times to allow for considerations that are used to investigate the efficacy of drugs or to incorporate new types of issues or information, such as preparations for bioterrorism and for other regulations regarding new developments in the manufacturing of drugs.
The FFDCA is concerned with medicinal drugs or drugs that are designed to treat, prevent, and cure, or that are used in the diagnoses of illnesses or diseases in people or animals.
Medicinal drugs are classified into two major categories:
- Prescription drugs that can only be dispensed with a written prescription from a qualified healthcare professional, such as a physician, dentist, etc. (e.g., Vicodin for pain control)
- Over-the-counter drugs that do not need a written prescription in order to be purchased (e.g., Tylenol for pain control)
The FFCDA makes an additional designation between chemical compound drugs and biologic drugs.
- Chemical compounds are drugs that are manufactured by combining specific chemicals in fixed proportions. These are the drugs that most of the big pharmaceutical companies market. They are often further broken down into:
- Brand-name drugs are patented and can only be manufactured and distributed by the company that holds the patent, such as Tylenol.
- Generic drugs are basically the same composition but manufactured by different companies under different names; often generic drugs are less expensive than the brand-name versions, such as acetaminophen, which is generic for Tylenol.
- Biologic drugs are composed of a wide range of different therapeutic products, such as vaccines, gene therapy materials, recumbent therapeutic proteins, and so forth. Unlike chemical drugs, biologics are manufactured in some type of a living organism or living system, such as a plant, animal, or even in a microorganism like a bacterium. These products require very strict regulations as they are highly sensitive to environmental changes, and even the slightest alteration in the conditions under which they are manufactured can affect their composition. Under this category, there are:
- Patented biologics can be manufactured and marketed only by the company holding the patent.
- Biosimilars are simply generic versions of biologics. These are rare because it is difficult for a company to establish that a biosimilar drug is equivalent to the original biologic in terms of its effectiveness and composition. The first accepted biosimilar drug in the United States was approved by the FDA in March 2015.
Biologic drugs are typically marketed as prescription drugs and are most often specialty drugs that are designed to have very specific uses.
Pharmaceutical Classification Systems
For lack of a better designation, this article uses the term pharmaceutical classification systems to refer to a number of drug classification methods that classify drugs according to their chemical composition, mechanism of action, or therapeutic intent. When one reads a drug guide or textbook on drugs, these materials will often use these types of grouping criteria to classify drugs into specific categories. When drugs are classified by their mechanism of action or therapeutic effects, certain drugs may be classified in more than one group. This results in a large number of potential classes of drugs.
For instance, antidepressant drugs are drugs that are primarily used for the treatment of clinical depression, although they have other uses as well. Antidepressant drugs are also classified according to their mechanism of action. Selective serotonin reuptake inhibitors, such as Prozac or Paxil, are primarily antidepressant drugs that act on the neurotransmitter serotonin, whereas tricyclic antidepressants, such as Elavil, act on three different neurotransmitters (dopamine, serotonin, and norepinephrine). In addition, certain selective serotonin reuptake inhibitors are used in the treatment of anxiety disorders and even personality disorders, and may be classified as drugs designed to treat those conditions as well.
Systems that are used for classifying drugs according to their chemical composition or mechanism of action are not limited to source guides or textbooks. Several organizations classify drugs according to these methods or methods similar to them. For example, the National Drug File – Reference Terminology is a system of classification used by the United States Department of Veterans Affairs that classifies drugs based on four categories:
- Chemical structure of the drug
- Cellular mechanism of action of the drug (or its sub-cellular mechanism of action)
- Organ or system level of the drug’s physiological effects
- Therapeutic intent of the drug
When drugs are categorized based on their shared effects, the result is typically 7-10 or even more major categorizations of drugs. Many drug manuals follow this particular classification system without regard to the potential for abuse of or addiction to the drug. The International Drug Evaluation and Classification Program, an organization of law enforcement professionals, classifies drugs according to seven categories that are used to identify and clarify the types of drugs a particular suspect may have been taking. The categories of drugs are listed by their major behavioral effects to allow training for law enforcement professionals that enables them to quickly determine what type of drugs a person may have been taking based on behavioral observations of the person. These seven major categories include:
- Central nervous system depressants: Central nervous system depressants are drugs that depress or slow down the functioning of the body’s systems. The central nervous system (CNS) consists of the brain and spinal cord, and it functions as the communication network for the body. These drugs do not necessarily cause one to become depressed (although taken in sufficient doses, they might have that effect on some people); however, they depress or dampen the communication channels between neurons and nerves. This results in reduced heart rate, reduction in breathing, lower blood pressure, etc.Drugs in this category include alcohol, benzodiazepines (anti-anxiety drugs) barbiturates (minor tranquilizers), many antidepressant medications (although some classification systems give antidepressant medications their own category), many drugs used in the treatment of psychosis (although some classifications placed drugs used to treat psychosis in their own category, calling them antipsychotic drugs), and others. Familiar drugs in this classification Xanax, Valium, Seconal, Zoloft, Prozac, Paxil, Thorazine, etc.
- Stimulants: Stimulants accelerate breathing, increase a person’s heart rate, result in an increase in blood pressure, and speed the overall processes of the body, including the processes of the CNS. These drugs also can increase a person’s energy level, improve a person’s attention, lead to an ability to focus better, and may enhance memory when taken in small doses. In larger doses, they may result in extreme hyperactivity, cause hallucinations, and lead to delusional or even psychotic behavior.Drugs in this category include amphetamines, cocaine (crack), caffeine, methamphetamine, and many diet aids. Familiar drugs are crystal meth, Ritalin, Adderall, Concerta, Provigil, Dexedrine, and so forth.
- Hallucinogenic drugs: Hallucinogens are drugs that are often used as sleep aids or hypnotic enhancers. These drugs affect the CNS, alter perception of reality, and may have a sedating effect; however, they can also have a stimulating effect. Many of these drugs were originally used as sleep aids or by psychiatrists as aids for therapy. Examples here include drugs like LSD, ecstasy (MDMA), psilocybin, mescaline, Ambien, and so forth.
- Dissociative anesthetic drugs: These drugs are used to inhibit the perception of pain. They also distort perception, especially vision and hearing, and produce a feeling of being detached (dissociated) from the environment, hence their classification. Ketamine (special K), PCP, and similar drugs are examples.
- Narcotic analgesic medications: Narcotic analgesics are medications that are primarily used in the treatment of pain and derived from opium or from the poppy plant (or synthetic chemicals similar to opium). These drugs produce marked euphoria and mood changes in people who use them. They include opium, heroin, morphine, Vicodin, OxyContin, codeine, Darvon, Demerol, and many others.
- Inhalant drugs: This category includes a wide range of breathable substances that are typically not sold as medications or drugs but marketed for other purposes. This category also includes anesthetics that are administered in the form of breathable gases. Examples include rubber cement, gasoline, paint thinner, hairspray, paint, etc.
- Cannabis products: This includes all products that contain the active ingredient delta-9 tetrahydrocannabinol (THC). This category includes marijuana, hashish, and synthetic drugs such as dronabinol.
Many pharmaceutical texts add to the above classes by including specific categories for antidepressant medications, antipsychotic medications, antihistamines, and so forth. There can be quite a large number of different categories of drugs in a specific classification scheme when the drug’s particular mechanism of action is considered as the method of classification. This is the case in many textbooks and on various drug information websites.
Schedule I Substances
Drugs in this classification are considered:
- To have a high potential to be abused
- To have no accepted medical treatment usage
- To lack an accepted safe protocol for use
The drugs in this schedule are illegal to own, manufacture, or distribute except under conditions specified by the DEA (this also includes synthetic versions of these substances).
Drugs in listed in Schedule I include:
- Certain opioid derivatives, such as heroin
- Certain hallucinogenic drugs, such as cannabis derivatives (e.g., marijuana), MDMA (e.g., ecstasy), methaqualone, peyote, and LSD
- Certain stimulant drugs such as fenethylline
Cannabis products, such as marijuana, remain classified as Schedule I substances by the DEA and the federal government, though certain states have allowed their use for medical purposes, and some localities have even allowed for individuals to possess small amounts of marijuana for personal use. The situation has resulted in some interesting speculation; in some states, a person may legally possess marijuana according to local laws, but be in violation of federal statutes.
Schedule II Substances
These substances are considered to:
- Have a high potential for abuse
- Have accepted medical use for treatment but typically only under certain conditions
- Result in severe physical dependence or psychological dependence if abused
Except under extreme conditions, no drug appearing on Schedule II may be dispensed without a prescription, and some may not be dispensed to the general public at all (e.g., cocaine). A few drugs under this designation include:
- Cocaine, which is still used in some cases as a topical anesthetic
- Amphetamines, including Adderall, Dexedrine, Ritalin, Concerta, and methamphetamine
- Certain narcotic drugs, including morphine, opium, codeine, fentanyl, methadone, oxycodone, and hydrocodone (e.g., Vicodin)
- Certain barbiturates medications, such as Seconal and Nembutal
- Phencyclidine (PCP)
Schedule IV Substances
Substances in this schedule:
- Have a lower potential for abuse relative to Schedule III substances
- Have evidence that they have currently accepted medical uses in the United States
- May lead to more limited physical or psychological dependence when abused, relative to Schedule III substances
Prescription of Schedule IV substances is similar to those in Schedule III. Drugs listed here include:
- Benzodiazepines, such as Xanax, Valium, Ativan, and Restoril
- Benzodiazepine drugs, such as Lunesta and Ambien
- The barbiturate phenobarbital
- Provigil (modafinil)
- Chloral hydrate
Schedule V Substances
Substances in this category:
- Are considered to have a low potential for abuse relative to drugs in Schedule IV
- Have accepted medical use in the United States
- May lead to limited physical dependence or psychological dependence relative to Schedule IV substances if abused
Like all the drugs classified in Schedules I-IV, these drugs must also be obtained with a prescription. Some of the drugs on this list include:
- Certain cough medications that contain very small amounts of codeine and have other active ingredients
- Medications that contain small amounts of opium or synthetic opium derivatives that are used to treat diarrhea
- Certain anticonvulsant medications, such as Lyrica
- Some antidiarrheal medications, such as Lomotil
Inconsistencies in the Placing of Substances in Schedules I-V
Overall, the classification system is relatively solid; however, even though the system appears to be strictly regimented, there remain a number of inconstancies in the DEA’s choices of where certain drugs should be placed. There are several special qualifications for certain drugs that appear to allow them to be placed in different schedules.
For example, Marinol, used to treat nausea associated with chemotherapy, actually contains the active ingredient found in cannabis. It is, however, classified as a Schedule III drug instead of a Schedule I drug because it has scientific evidence for its medicinal uses, whereas cannabis itself remains on Schedule I. Of course, this inconsistency simply fuels the already heated debate regarding the legalization of marijuana, and conspiracy theories regarding its medicinal properties and the pharmaceutical industry being behind a plot to keep it illegal.
Several other inconsistencies can be found with other drugs, such as the observation that there is no scientific evidence that LSD (Schedule I) is addictive. In addition, there is some evidence from the field of psychiatry for potential therapeutic properties for the drug in that context.
For complete listings of all medications and Schedules, refer to the United States DEA website.
Do These Drugs Always Remain in the Same Classification Schedule?
Drugs can be assigned to different schedules, depending on available evidence and may even be removed from the classification scheme as new evidence develops. For instance:
- Hydrocodone, which is the active ingredient in narcotic pain medications, such as Vicodin and OxyContin, was formally transferred from Schedule III to Schedule II in 2014 due to the large number of individuals who abuse the drug and new research evidence indicating that it had a higher potential for the development of abuse and addiction than previously believed.
- The painkiller Tramadol was not put on the controlled substances Schedules until 2014 when the DEA decided that it belonged on Schedule IV based on new evidence that it had a potential for abuse.
- Recently, the DEA removed the drug Naloxegol, an opioid drug that is used to relieve constipation that is associated with use of narcotic drugs, from the classification scheme entirely.
Over 160 substances have been added, moved, or removed from the classification scheme since its inception.
There is no singular medication or drug classification system used in the United States, and one can find inconsistencies in the major classification systems that are used. The most controversial legal classification of a drug today concerns the scheduling of marijuana by the United States Drug Enforcement Administration as a highly addictive drug with no medical uses (Schedule I). Drugs are typically classified by their chemical structure, mechanism of action, therapeutic effects, and/or potential for abuse.