I guess that's a good thing for you. I'm also surprised the pseudoephedrine didn't cancel it out.

This means that altough at low doses it is a safe and effective painkiller, exceeding the stated dose by a significant amount is likely to lead to acute liver failure and death due to the paracetamol/acetaminophen.

In fact overdoses (accidental or deliberate) of medication containing paracetamol/acetaminophen are the most common cause of acute liver failure in the US.

So, by all means use this effective painkiller, (though possibly not while driving or operating machinery due to the opiate nature of codeine), but don't even think about doing it for fun, overdoses kill.

• Drinking too much Benilyn with codeine will give you the raging shits
• Getting a cold water extraction wrong could cost your life or at least do some serious liver damage.
• In contrast to the first point - repeated use of codeine will make you constipated
• Repeated use of codeine will make you addicted - it's an opiate, it's metabolised to something similar to morphine by the time it hits your brain.
• Repeated use of codeine (and codeine containing medications) can have other odd effects. A friend of mine who had a serious habit ended up with skin so sensitive that if you touched her you would leave hand marks.

I felt pretty darn good taking cold & flu tablets last year (I think 20 mg codeine per 2-tablet dosage). By the end of the 3 or 4 days that had worn off a bit though.

O-demethylation is carried out by the enzyme CYP2D6. There are several dozen genetic variants of CYP2D6, and the activity of the enzyme varies widely among the variants. Most of the work has been done looking at the -3 and -4 family of variants; these are inactive enzymes. If you have one copy of one of these alleles, most of the codeine undergoes glucorinudation (the "other pathway"), leaving little or no morphine production. If you have two copies, you get no morphine. It is nearly impossible to get a person with CYP2D6-3 or -4 addicted to codeine; codeine alone simply isn't strong enough. It has to be converted to morphine.

Anywhere from 20-60% of the population has one of these inactive forms, depending on your ethnicity (whites=20%, asians=60%, IIRC). However, there are also hyperactive forms. Which variant it is escapes me, but IIRC it's present in less than 10% of the US population as a whole.

If you have one of these forms, the majority of the codeine you ingest is converted to morphine, and that's why you can't walk. You're a lightweight. Sorry, it's just your genes.