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Drug Classifications

Addictive drugs may be classified as Stimulants, Depressants, Hallucinogens, or Opioids on the basis of their effects. Furthermore, the United States government classifies addictive drugs as controlled substances in five schedules.

Drug Classifications: Law and Science

From common medications to illegal narcotics, drugs abound all over the world. A drug is any substance that alters the physiology, sensation, or cognition of an organism. Since thousands of drugs exist, scientists tend to categorize them into broad classifications on the basis of their shared chemical properties and effects on the human body and mind.

Since many drugs are dangerous and addictive, every country in the world also classifies some drugs or categories of drugs as controlled substances. Drugs become controlled substances when a country’s laws restrict people from consuming, possessing, manufacturing, transporting, buying, or selling them within the government’s jurisdiction. In some cases, a controlled substance may be illegal for anyone to use for any reason. In other cases, the law may impose limits on how a controlled substance may be used legally, such as exclusively for medical prescriptions or scientific research.

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Drug Classifications By Effect

Both legal drugs and controlled substances can the sources of addiction. In general, addictive drugs may be classified as Stimulants, Depressants, Hallucinogens, or Opioids. These four drug classifications separate substances by how they interact with the brain and alter a person’s mindset and behavior.


Stimulants are a class of drugs which enhance central nervous system activity and block the re-uptake of the neurotransmitters norepinephrine and dopamine. Norepinephrine enhances arousal, memory, and attention, while dopamine reinforces a person’s inclination to positive stimuli.  A typical Stimulant will cause a “rush” of euphoria and wakefulness, accompanied by heightened breathing, heart rate, and blood pressure. In larger doses, Stimulants may cause heart failure and seizures.

Doctors prescribe some Stimulants as medication for ADHD and narcolepsy. People also use Stimulants without a prescription to stay active and alert while working, studying, or exercising. Caffeine is the most commonly used Stimulant in the world. The illegal recreational drugs Cocaine, Methamphetamine, MDMA (Ecstasy), and Cathonine are also Stimulants.


Depressants are drugs that impair the activity of the central nervous system by enhancing the effects of GABA, a neurotransmitter which inhibits connectivity among neurons. Depressants typically make a person feel calm or drowsy.  Since depressants sedate the brain, doctors prescribe some of them as medications for sleep disorders, anxiety, and stress. The two sub-categories of prescription depressants are Benzodiazepines and Barbiturates. Depressants have the potential to cause addiction and overdose, and they can cause side-effects such as slurred speech, dizziness, and loss of coordination. Alcohol is perhaps the most widely-abused depressant in the world.


Hallucinogens are mind-altering drugs which cause false perceptions of reality. A hallucinogen may distort how a person experiences time, motion, colors, and sounds. Hallucinogens affect the brain’s levels of serotonin, a neurotransmitter which regulates cognition and memory. Some Hallucinogens also cause dissociative effects by interfering with the functioning of the excitatory neurotransmitter glutamate. Dissociative Hallucinogens cause sensations of detachment from reality as well as hallucinations. The effects of a Hallucinogen will depend on the drug and vary from person to person. Mescaline, DMT, LSD, and Psilocybin are examples of non-dissociative Hallucinogens. Ketamine and PCP are both dissociative Hallucinogens. Almost all Hallucinogens are controlled substances in most countries.


Opioids are drugs which originate naturally in the Opium poppy plant. Synthetic Opioids like Fentanyl are manufactured to imitate the chemical structures of natural Opioids like Morphine. Opioids block sensations of pain by binding to the brain’s Opioid receptors. Doctors prescribe Opioids to treat moderate to severe pain.  Opioids also cause intense sedation and euphoria. Since Opioids pose serious risks for addiction and overdose, most Opioids are Schedule I or II controlled substances. Throughout the world, drug traffickers manufacture and sell Opioids as counterfeit painkillers or recreational drugs. From 1999 to 2017, illegal and prescribed Opioids killed about 400,000 Americans.

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Drug Scheduling Under The Controlled Substances Act

In the United States, the federal Controlled Substances Act categories controlled substances into five schedules. The drugs which fall into these legal classifications are variously restricted on the basis of their accepted medical usefulness and potential for abuse and addiction. The Drug Enforcement Administration is the federal agency primarily responsible for enforcing the Controlled Substances Act, even in states with drug laws in conflict with federal law. The following is an overview of the five drug schedules under the Controlled Substances Act.

Schedule I

Schedule I controlled substances are drugs which the federal government considers to pose high risks for abuse and addiction and lack any proven medical value. In other words, they are entirely harmful. The legal penalties for drug offenses involving Schedule I controlled substances are severe. Some of the most well-known Schedule I controlled substances are the Hallucinogens Psilocybin, LSD, Mescaline, and DMT, the Opioid Heroin, the Stimulants Cathinone and MDMA (Ecstasy), and a variety of Fentanyl and Morphine analogs. Marijuana, one of the most common drugs in America, is also a Schedule I controlled substance.

Schedule II

Schedule II controlled substances also pose high risks for abuse and addiction. However, Schedule II controlled substances have accepted medical value, so they may be legal as medications. Nevertheless, these drugs are often likely to cause severe dependence and overdose. It is illegal to acquire a controlled substance as a medication without a prescription.

Many Opioids are Schedule II controlled substances. These include Codeine, Fentanyl, Methadone, Morphine, Oxycodone, Hydrocodone, Hydromorphone, and Meperidine. The popular Stimulants Cocaine and Methamphetamine are also Schedule II controlled substances, as are raw Opium, PCP, the Barbiturates Pentobarbital and Amobarbital, and the Stimulant Methylphenidate, the generic name for the “study drugs” Ritalin and Concerta. The most famous study drug, Adderall, is a Schedule II controlled substance as well.

Schedule III

Schedule III controlled substances pose lower risks for abuse and addiction than substances in the first two drug classifications. As prescription medications, Schedule III controlled substances are less likely to be abused or cause dependence than Schedule II controlled substances, although they still pose moderate risks for dependence. Anabolic Steroids, most Barbiturates, the Opioid Buprenorphine, the Hallucinogen Ketamine, and Tylenol combined with Codeine belong to this category.

Schedule IV

Schedule IV controlled substances pose lower risks for abuse and addiction than Schedule III controlled substances. Most Benzodiazepines and similar sedative-hypnotic drugs are Schedule IV controlled substances. These include Valium, Xanax, Librium, Klonopin, Halcion, Restoril, Ambien, and Lunesta. The Opioid Tramadol is also a Schedule IV controlled substance.

Schedule V

The federal government considers Schedule V controlled substances to pose the lowest risks of abuse and dependence. The category includes some medications for coughing, stomach pain, and seizures.

Start Rehab Today For Drugs Of Any Classification

If you or someone you know is struggling with addiction to any drug, today is the day to reach out for help. Please contact a dedicated treatment provider today to learn more about the many options for inpatient and outpatient rehab for drug and alcohol abuse.

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