@Mitch there's a lot to unpack here, depending on how many of the questions in the transcript you want answered. So here goes: Dr. M.A.R., or how I learned to stop worrying and love the NSAID cc @Cerb
@tchrist is right on all points, because of course he is. But first off, should you take painkillers every day and what happens if you do?
Painkillers are designed for acute pain, not chronic. The ideal situation is that they should relieve pain until you can discontinue them, unless you have some chronic debilitating pain that will return. But relieve they should, and if they don't you need to switch drugs or drug classes until they do.
For headache, if you use painkillers every day, you will easily get Medication Overuse Headache. It's commonly seen with both NSAIDs and triptans (i.e. sumatriptan) for migraine headache. If your headache persists, either you are underdosing, or your headache is misdiagnosed and not treated properly. The most common people with MOH are people who have migraines and take NSAIDs, which are only marginally effective.
So, for example, no more than two sumatriptan pills are allowed per day, each 100 mg.
The underlying mechanism is probably sensitization of whatever pain mechanisms.
Next, acetaminophen: Max allowable dose is 4 g/d. In alcoholic patients, it's 2 g/d. In individuals otherwise susceptible, liver toxicity can occur at 3.25 g/d dose. Here, each pill ranges from 325 mg to 500 mg acetaminophen. Meaning, 8 pills can cause serious liver damage.
How does toxicity occur? The liver normally metabolizes acetaminophen by binding it to a molecule of glucose, making it more polar and excreble in urine. A high dose saturates this pathway easily, so the liver instead chooses to change the acetaminophen molecule to make it more polar. The resulting compound is an electrophile, meaning, it's an organic molecule that likes binding to functional groups that have electrons. Proteins and DNA are full of those functional groups.
Thus, electrophiles are always toxic because they bind DNA and proteins, rendering them dysfunctional. Many carcinogens are electrophiles, for example. Many anticancer drugs are electrophiles. Acetaminophen's transformed metabolite is also an electrophile.
The drug is easily accessible, increasing the likelihood of using it for suicide attempts. BUT liver failure is extremely painful and rarely lethal because they're discovered and treated for toxicity promptly, so there are much less painful and surer methods to commit suicide using drugs.
TCh is also right that toxicity happens accidentally, because combination painkillers tend to have some acetaminophen, and so do cold pills. Someone taking several of these at once is getting acetaminophen from multiple sources.