Don't forget the other major variable in the "levels" debate. This is individual rates of metabolism. Alcohol is very different to other drugs in this regard but depending upon how quickly a person processes alcohol, metabolites are also likely to be there for different times with different people.
What makes alcohol very different to other drugs and individual responses is that the body has a built in mechanism for coping with regular or larger amounts of alcohol by making more enzymes (dehydrogenases, reductases and oxidases). The fructose-> glucose regenerated co-enzyme NADH is then almost completely prioritised to metabolising alcohol.
From my post on:
Alcohol who considers it a drug
Moles, enzymes, 2 step & NAD+
On a molar basis, alcohol is consumed in far greater amounts than any other drug. A few drinks often involves more than a mole or two (1mole = 46g) being consumed. A “large” session may involve a MDMA molar equivalent of more than 1000 tablets, as 1 mole of MDMA HCl is 229g.
Posted by Pleo, this thread also contains an excellent basic graph comparison of duration of effect of various drugs and alcohol.
So, while variations exist between the metabolism of non-drinkers to regular drinkers to large drinkers to those with metabolic disorders to those on other medications etc., homeostasis ensures most people fit the gaussian 95% rule. The system for metabolising alcohol is therefore robust and relatively consistent between different people, even taking into account variations in race, background etc.
While this is also somewhat true with most drugs (take more & body attempts faster elimination) the variations in elimination may be considerable, among other things varying with water intake, previous food and drug consumption, fitness and other factors. This variation can be quite a bit more than for the alcohol model, as many people metabolise drugs via alternative routes compared to alcohol which can take either of 2 routes for each stage of catabolism (2) before being eliminated as acetic acid. (Note: this model is representative of a person with no liver or metabolic disease)
We know that as many as 1 in 10-20 people may have a P4502D6 deficiency (ethnicity and genetics being factors). This is the body's preferred metabolic path for MDMA, which due to kinetics involved in alternatives, also makes this the fastest pathway (other variations not considered).
We also know that MDMA is antidiuretic in effect. Some are affected by this more than others. What sort of variation exists if someone pees every 3/4 of an hour while someone else doesn't pee for 3-4 hours? Then there's Joe in the corner drinking a couple of lite beers and has no trouble pissing as the alcohol is diuretic in function and "overrides" effects from MDMA.
Then we have poly use or medication interactions which may not directly contribute to cause any noticeable additive affect, yet metabolism of both substances may be substantially changed or lengthened.
These are just some quick examples I can think of. With proposed testing, drugs are a pandoras box compared to alcohol. As for the "show positive - be charged with 3 offences"; I think there will be a large increase in reported drink spiking. after-all, if you say you didn't take anything and stick to that story, who's to say in this day and age that you weren't slipped a mickey?
