Fast acting pain medication

Hello Everyone,

I might have asked this question before, but I can’t remember. I’m a chronic pain patient and last night was absolutely horrible. I spent hours passing for the pain to stop. I took some oxycodone and as usual it took about a 1/2 an hour to work. That I get, it has to process through your stomach.

But as I was sitting there at 3am in agony I thought about the times I was at a hospital and they injected me with morphine or other drug and how quickly it worked. The pain relief was instantaneous whet it was injected into a vein or into muscle.

So my question is, how is that possible. My understanding is that opioid pain killers work by binding to and blocking your opioid receptors in your brain. How can an injected drug travel so QuickTime to your brain? It’s like the blood in your body is traveling at the speed of sound. How does it work so fast?

The average* speed of blood flow is around 2-4 MPH, so from a vein in your upper arm to the brain is just a couple of seconds. IANAD, but I suspect you may have had some unconscious placebo effect from knowing that they were giving you morphine or whatever, and the actual analgesia began about five seconds later.

  • It’s hard to pin down as blood flow is pulsing, rather than steady, and flow through capillaries is more of an ooze compared to leaving the heart through the aorta.

Already sufficiently answered, but thought I’d give some detail as to how short a distance the blood with drug has to travel to get to brain. When injected, drug travels from injection site to right atrium of heart (where vena cava enters heart, in so many words), then through valve into right ventricle that then pumps drug-laden blood to lungs and goes through a very broad system of capillaries of lungs en masse via the pulmonary arteries. Blood is then returned via pulmonary veins to left atrium/ventricle (the ‘strong-pump side’ of oxygenated blood). It exits heart into aorta which has an arch almost right away to allow arteries to exit off to upper/lower parts of body. IIRC, the vessels supplying heart muscle are first to branch off and just after that portion there are a number of vessels that go directly upwards to brain, thus inducing med(s) effect.

I know this is an imperfect description, but it shows just how short a distance it is from, say an injection in antecubital IV (ie IV site at anterior elbow area) to the brain. There are a LOT of capillaries in lungs, so time of transit is quick through lungs to heart’s left ventricle, fwiw. Once the blood is pumped into the aorta, its only gotta go maybe less than a foot or so to get to brain and effects felt. Of course, not all of the entire dose goes to brain at once due to some dilution, but it doesn’t take long for much of the dose to begin its effects as the blood is recirculated systemically constantly.

When a drug is taken orally, it takes time to dissolve and enter vascular system ‘osmotically’ through stomach/intestinal wall(s), so effects take significantly longer, especially if it is a ‘timed/extended release’ type of pill. Huge difference in time of person feeling effects (as already noted in prior posting, of course). If OP wants to see the pathway here’s a decent link to anatomy of vessels involved (quite a few pictures of different views of mediastinum) between venous side of heart -v- arterial side and arteries to brain that may be of interest. Its a subscription site, but allows you to view images without the names of vessels included (just click on “Use free version” pop-up, fwiw).

Hope this helps to better understand how short a distance it actually is from IV site to brain overall :slight_smile: