What is an opioid?

An opioid is a drug that acts on the body's opioid receptors, and the class includes prescription pain medicines, medicines for opioid use disorder, and illegal drugs such as heroin. The word is a pharmacological label. It says what a drug does in the body, and it is separate from the legal word narcotic, from a drug's DEA schedule, and from its UK class.

How do official sources define an opioid?

The National Institute on Drug Abuse (NIDA) puts it this way on its opioids page:

Opioids are a class of natural, semi-synthetic, and synthetic drugs. These include both prescription medications used to treat pain and illegal drugs like heroin.

NIDA then sorts the class by how its members are made. Natural opioids such as morphine, codeine, opium and thebaine come from the seed pods of the opium poppy. Semi-synthetic opioids, including heroin and the pain relievers oxycodone, hydrocodone and oxymorphone, are made in laboratories by chemically processing natural opioids. Synthetic opioids such as fentanyl are manufactured entirely in laboratories. NIDA also lists the main prescription uses as the treatment of pain, and says opioids can help treat cough or diarrhea.

A short test follows from the definition. If a drug's own label describes it as an opioid agonist, or says it works at the mu-opioid receptor, it is an opioid. If the label describes some other mechanism, it is not, whatever the drug is used for and however strongly it is controlled.

What is the difference between an opioid, an opiate and a narcotic?

NIDA says the natural substances made from the opium poppy "are also known as opiates". So an opiate is a natural opioid, and opioid is the wider word that also takes in the semi-synthetic and synthetic drugs. In practice many people use the two words as if they meant the same thing, and in speech that rarely causes trouble.

Narcotic belongs to a different system. It is a legal category in the Controlled Substances Act, defined at 21 U.S.C. 802(17) as opium, opiates and their derivatives (but not the isoquinoline alkaloids of opium), poppy straw, coca leaves, cocaine, ecgonine and its derivatives, and any compound, mixture or preparation containing any of them. The DEA list marks drugs that meet its narcotic flag with a Y. The overlap with opioids is large and not complete: cocaine is legally a narcotic but is a stimulant and not an opioid. The guide on what a narcotic is sets out the statute and the flag in full, with a table of this site's 18 drugs.

Which drugs on this site are opioids?

Three of the 18 are opioids, and each label says so in its own words.

• Tramadol. The mechanism section of the Amneal tramadol label says: "Tramadol hydrochloride tablets contains tramadol, an opioid agonist and inhibitor of norepinephrine and serotonin re-uptake." Its indication is pain "severe enough to require an opioid analgesic". The DEA list shows Schedule IV, NARC Y. UK: Class C, Schedule 3. See tramadol.
• Fentanyl. The Hospira fentanyl citrate injection label says "Fentanyl is an opioid agonist". The indications are for use during anesthesia and in the immediate postoperative period. The DEA list shows Schedule II, NARC Y. UK: Class A, Schedule 2. See fentanyl.
• Buprenorphine. The Suboxone label says buprenorphine is "a partial agonist at the mu-opioid receptor and an antagonist at the kappa-opioid receptor", and the product is indicated for treatment of opioid dependence. So it is an opioid that is used as a treatment for opioid use disorder. The DEA list shows Schedule III, NARC Y. UK: Class C, Schedule 3. See Suboxone and buprenorphine.

The Suboxone product also contains naloxone, which its label calls an opioid antagonist. Naloxone is not an opioid in the sense used here, because it blocks the receptor and does not stimulate it.

Is ketamine an opioid?

No. The Ketalar label, published by Par Health on March 26, 2026, says "KETALAR is a general anesthetic", and its indications are as the sole anesthetic for procedures that do not require skeletal muscle relaxation, for induction of anesthesia, and as a supplement to other anesthetics. The mechanism section says ketamine is "a non-selective, non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor". That is a different receptor system from the opioid one. The DEA list places ketamine in Schedule III with a NARC flag of N, and the Home Office lists it as Class B, Schedule 2. Ketamine is controlled, but it is not an opioid and not a narcotic in the legal sense. The page on ketamine gives the details.

Are gabapentin and pregabalin opioids?

No, in both cases. Section 9.2 of the Neurontin label (Viatris, DailyMed, published August 6, 2026) says:

Gabapentin does not exhibit affinity for benzodiazepine, opioid (mu, delta or kappa), or cannabinoid 1 receptor sites.

Gabapentin is not federally controlled, and the label says so. The UK treats it as a Class C drug in Schedule 3. Pregabalin is the closer case, since it is a Schedule V drug in the US with a NARC flag of N. The Lyrica label says it "binds with high affinity to the alpha2-delta site" of voltage-gated calcium channels, and its section 9.1 says Lyrica "is not known to be active at receptor sites associated with drugs of abuse". It is also Class C, Schedule 3 in the UK. Neither drug works through opioid receptors, so neither is an opioid, although the two are often mentioned together with opioids in discussions of misuse and overdose. See gabapentin and pregabalin (Lyrica).

Which other drugs here are not opioids?

None of the remaining drugs on this site acts as an opioid. The benzodiazepines (alprazolam, clonazepam, lorazepam, diazepam) and zolpidem act on GABA-A receptors, and the guide to benzodiazepines covers them. Amphetamine, lisdexamfetamine and phentermine are stimulants. Testosterone is a hormone. Trazodone is described on its label as a selective serotonin reuptake inhibitor, cyclobenzaprine is a muscle relaxant and hydroxyzine is an antihistamine, and none of those three is a controlled substance in the US. The distinction between "controlled" and "opioid" is worth keeping, because several controlled drugs here have no opioid action at all.

Why do labels pair opioids with other drugs in warnings?

The boxed warning on benzodiazepines such as Xanax begins with the risks from concomitant use with opioids, and says that the combination "may result in profound sedation, respiratory depression, coma, and death". That is why opioids and benzodiazepines are discussed together even though they are different classes. The opioid label for tramadol carries its own boxed warning on addiction, abuse and misuse. We do not repeat dosing or combination advice here. A person taking either kind of medicine should ask their prescriber or pharmacist about their own situation.

What is naloxone?

Naloxone is a medicine that reverses the effects of an opioid overdose. On March 29, 2023, the US Food and Drug Administration approved Narcan naloxone nasal spray for over-the-counter, nonprescription use, which it described as the first naloxone product approved for use without a prescription. The FDA noted that other formulations of naloxone remain prescription only, and that the timeline for availability and price is set by the manufacturer. NIDA's current advice is that anyone who suspects an overdose should call 911 and use naloxone if it is available.

Where to get help

This site reports legal and regulatory facts and does not give medical advice. In the US, the 988 Suicide and Crisis Lifeline (call or text 988) can help with a substance use or mental health crisis, and Poison Help (1-800-222-1222) answers questions about a possible poisoning. In an emergency call 911. In the UK, call 999 in an emergency or NHS 111 for urgent advice. For how opioid drugs sit in the legal lists, see DEA drug schedules and UK drug classes, and for the wider idea of a controlled drug see what is a controlled substance.

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