Chemical Class versus a Drug Class

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Drug class and chemical class are often used interchangeably and confusingly, so I have developed the standardized definitions below. I have seen midazolam referred to as a "benzodiazepine agonist." To me, this is confusing because the combination of words implies that midazolam is an agonist of this thing called benzodiazepine, which represents the main functional group of midazolam. Maybe, they are saying that it is an agonist that happens to be a benzodiazepine. The confusing part of interpreting it this way is that

  • Drug Class - A drug class is a group of drugs that have been organized according to its biological target and its effect on the target (agonist, antagonist, inverse agonist, partial agonist, etc.). Commonly, the biological target of the drug class is its primary biological target. However, one drug can have several drug classes. For example, morphine is a μ opioid receptor agonist. Morphine is also a δ and κ opioid receptor agonist, but to a lesser extent than a μ opioid receptor agonist.
    • Agonist- Stimulates the receptor. For example, a GABAA receptor agonist stimulates chloride ion flow from the outside of the receptor to the inside of the GABAA receptor.
    • Inverse Agonist- Stimulates the receptor in the opposite way. For example, a GABAA receptor inverse agonist stimulates chloride ion flow from the inside to the outside of the GABAA receptor. An agonist and inverse agonist stimulate a receptor in opposite ways, so the designation of a drug as an agonist or an inverse agonist is technically arbitrary. However, drugs that are discovered first to stimulate receptors are called agonists. When a drug is discovered to have the opposite effect on the receptor, then they are given the designation of inverse agonists.
    • Antagonist- inhibits the function of the receptor. In the case of the GABAA receptor, an antagonist inhibits the function of the receptor.
  • Chemical Class - A chemical functional group that is common among a group of drugs. A drug can be from the same chemical class and be in a different drug class.


Drug/Chemical Class
Drug Drug Class Chemical Class Molecular


Chemical Class


Midazolam GABAA receptor


benzodiazepine Chem001.png Chem002.png Midazolam (Wikipedia)

Benzodiazepine (Wikipedia)

Benzodiazepine (Chemspider)

Morphine μ opioid



Morphine (Wikipedia)


  • Below is a procedure for determining the drug and chemical of a particular drug.


  1. Look for the drug on Wikipedia. Let us look at the drug Midazolam.
  2. In the first few sentences, look for something that sounds like a functional group. In the example Midazolam, we have the word benzodiazepine. This is the chemical class. However, the drug class (as define above) is not clearly stated.
  3. What is the main target? In the Wikipedia entry for Midazolam, its main biological target is the GABAA receptor.
  4. Is the drug an agonist or antagonist? A search on the Wikipedia page does not clarify things, so I do a Google search. You go through the Google search with your drug and agonist or antagonist (e.g., "midazolam GABAA receptor agonist" or "midazolam GABAA antagonist").
  5. Then you look through the Google searches to see how it is associated. Determining the association can be tricky because

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