The Effects of Caffeine on Pain
Did you know that caffeine in its various forms is considered a psychoactive agent? Psychoactive means it has a stimulating effect on the central nervous system. Given its effects on the nervous system, some even consider this substance a drug.
Did you know that surveys show that almost all adults (up to 95 per cent) ingest some form of caffeine everyday? Many people have a total caffeine intake up to 400 mg/day (that's considered a high level). That may not be surprising when you consider caffeine is a substance in a variety of beverages as well as some foods and medications.
You probably know about caffeine in coffee and tea, but don't forget soft drinks, energy drinks, and chocolate. There is caffeine in many over-the-counter drugs (for cold symptoms, headache pain relievers) and some prescription medications. Some people even take caffeine pills to stay awake and alert.
Why is caffeine added to other pain relievers such as acetaminophen (Tylenol) or ibuprofen? Adding caffeine to an analgesic (pain reliever) seems to boost its ability to decrease pain. This effect is called adjuvant analgesia and its most noticeable with headache pain. Caffeine as an adjuvant analgesic doesn't seem to be as good for postsurgical pain.
Why does caffeine reduce headache pain? Caffeine is a vasoconstrictor -- that means it closes down or narrows the blood vessels. The effect is to reduce the amount of blood flow to an area.
If you have a "throbbing" headache, it's often because there is too much blood flow to the brain. Caffeine reduces the blood flow and thus decreases the pain. You could get the same effect (vasoconstriction of blood vessels in the head) by putting your feet in a bucket of ice cold water because blood would be diverted from the head to warm the feet. But you can see why an over-the-counter headache medication containing caffeine would be easier and less uncomfortable to use.
But as anyone knows who uses caffeine in any form on a daily basis, there are withdrawal symptoms. Headache is the number one withdrawal symptom experienced by most people. Fatigue is another common effect of caffeine withdrawal. In fact, anyone getting ready for surgery or fasting for blood tests who consumes caffeine on a regular basis can expect to have a headache from the caffeine withdrawal.
How does caffeine work that it can reduce pain and/or help other pain relievers provide pain relief? The mechanisms aren't clearly understood but in simple terms, caffeine blocks pain receptors.
Newer studies show that low doses of caffeine may actually have the opposite effect: it inhibits blocking pain receptors. What does this new information mean for us? It's possible that a cup of coffee or tea (or small amounts of other foods and beverages containing less than 100 mg of caffeine) could prevent other pain relievers from working. This same inhibitory effect of low doses of caffeine has been observed with acupuncture and electrical stimulation.
Researchers aren't quite ready yet to say we should avoid caffeine before acupuncture treatment or when using electrical stimulation to control pain. Further studies on the effects of varying doses of caffeine are needed before any specific guidelines on caffeine use can be determined.
Jana Sawynok. Caffeine and Pain. In Pain. April 2011. Vol. 152. No. 4. Pp. 726-729.