Antagonist, Inverse Agonist, Same But Different

We have our first exam coming up this week, on six full weeks of material. The two-day test will cover biochemistry, anatomy, histology, pathology, and a bunch of other –ologies I don’t understand either.

Yes, I’m writing this to procrastinate, no, it’s not a good use of my time, and no, grandma, I don’t need a brownies care package. Your last one turned me prediabetic as it is. Thanks though.

In reviewing last week’s notes I came across our Intro To Pharmacology class, a two-hour lecture by a renowned professor of, you guessed it, pharmacology. The lecture (entitled “Receptor Thinking for Physicians,” which was bad news right off the bat) came immediately before a full week of learning about metabolism, so its time placement seemed questionable at best.

The professor put on the mic and started his lecture at ten sharp. Though it was immediately obvious that this guy really knew his stuff; unfortunately for us, he sounded a little bit – okay, a LOT – like the Russian cosmonaut from Armageddon (THIS IS HOW WE FIX PROBLEM ON RUSSIAN… SPACE… STATION!). This made paying attention somewhat challenging on a Monday morning.

Remember this guy?

Language barriers aside, most of us who weren’t online shopping or trolling Facebook were with Cosmonaut for the first twenty minutes, until he reached a part of the presentation about “agonists” and “antagonists.”


In very brief terms, an agonist is a drug that “does” something, while an antagonist is a drug that “blocks” normal action.

That sentence took like 45 minutes to explain during class, probably because most of the class grew up with “antagonist” meaning “the evil queen from Power Rangers.”

Or maybe that’s just me.  Her name was Rita Repulsa, but I didn’t want to get too far off the rails here.

Anyway, once we got the concept down, the lecturer went on to explain the difference between an “inverse” agonist, which reduces the activity of something – think of gearing down in a standard transmission car – and an antagonist, which prevents other compounds from activating the thing. Best example I can think of is setting up a roadblock to prevent traffic. Here’s how he explained the difference (remember, cosmonaut voice):

“Inverse agonist, antagonist, looks like same, actually different. Next slide.”

Wait, what? I looked around the room; everyone had that unnerving slack-jawed expression you normally see on patients who just underwent electroconvulsive therapy. (Get it?! Unnerving!? Ha! Sigh. I’ll go drown myself in my bathtub now.)

Given that my class contains ninety-nine Type-A personalities who got through premed as undergrads by sitting in the front and understanding everything, Mr. Cosmonaut was promptly deluged by a flood of confused/angry/somewhat snotty-and-simultaneously-justified questions.  I’d never seen someone raise a hand in a manner one could characterize as “aggressive” until that day.

I didn’t understand the difference – far from it – but I mostly wanted Cosmonaut to run through his other 59 slides so I could go eat lunch and stop thinking about science for a few minutes.

Alas, it was not to be.  Twenty minutes later we got to another confusing section: the difference between potency and efficacy. Considering that I don’t know what either of those terms mean in normal English, I didn’t exactly have a light bulb moment when Cosmonaut said, “Efficacy, potency, sort of different, very similar, you see on lines on slide they are alike. Next slide.”

Just so you don’t think I’m being melodramatic, here’s his slide (don’t try to understand it):


Yeah. That makes exactly as much sense as you think.

Again, about thirty hands went up. Cosmonaut spent another twenty minutes trying to explain something about the difference between curing sick mice that he sickened in the first place, then murdering them with massive doses of some new beta blocker. Two weeks later I still have no idea what he is talking about, but at least I’m pretty sure I don’t want to work in a mouse lab.

Thank sweet baby Jesus in a tuxedo T-shirt for pass/fail curricula. P=MD!

3 thoughts on “Antagonist, Inverse Agonist, Same But Different

  1. Happy to try and help you understand antagonists and inverse agonists if you want. Short answer is that some receptors signal without the agonist being present. In those cases, an inverse agonist turns “off” the basal signal.

  2. Pingback: Back To School III | Laughter is the Best Medicine

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