Driving while not-drunk
November 17, 2011 6:51 PM   Subscribe

If my tolerance to alcohol increases, does my BAC go up more slowly?

I saw this question - which is basically the reverse of my question - but I'm still confused.

My tolerance for alcohol is pretty high right now. I am 130-lb woman (which is a healthy weight for my height), and if I have 3oz of 40-proof liquor, I don't feel drunk at all - I "feel" safe to drive.

However, according to a couple of online BAC calculators, that would put me at around .07 BAC. I realize that I can't rely on an online calculator, but since the legal BAC driving limit in my state is .08, I would prefer not to risk driving with a BAC of .07. I am concerned about both safety and legality.

So - if I don't feel drunk AT ALL, is it still possible for me to have BAC of .07?

I guess I could buy a breathalyzer, but I would rather not bother. (Sub-question if you think I should buy one: Amazon.com has breathalyzers starting at around $10 - are they reliable at all?)

Please note that I would never, ever drive if I felt buzzed. I am trying to be responsible, and figure out when it is both safe and legal to drive.

You can reach me at askme.anon.y.mouse@gmail.com
posted by anonymous to Health & Fitness (12 answers total) 3 users marked this as a favorite
I also wonder this but unlike you I own a breathalyzer. This device has provided endless amusement but it seems to me that tolerance increases ability to maintain consciousness and appear more sober but does not lower BAC. I hope that someone else will be able to confirm this.
posted by boobjob at 7:03 PM on November 17, 2011 [1 favorite]

I used to work in an alcoholism lab and I can tell you that everyone's subjective sense of buzz lines up with their actual BAC differently (we did formal lab experiments on this by getting people drunk in the lab and asking them questions and giving them tests), and that your sense of impairment is never a safe indicator. Real breathalyzers are more expensive than $10 and must be calibrated and used carefully to give an accurate result, so they're fun to play with but I wouldn't rely on anything you get for under $100 on the internet to give you readings that you will actually base decisions on. Even if you feel fine, you're probably impaired at least to some degree and the only way to be sure you are not is to wait it out.
posted by slow graffiti at 7:14 PM on November 17, 2011 [2 favorites]

(sub-answer only) We used to own a super cheap ($20?) breathalyzer, and although it was entertaining, interesting, and occasionally useful in helping convince party guests that they should not be driving, it was no where near consistent enough to trust anyone's safety or driving record with. It also died after just a few months. My feeling is that you have to spend quite a lot to get one that's even close to reliable.
posted by crabintheocean at 7:25 PM on November 17, 2011

As the other question's answer states, your BAC does not change. It's a concentration, you'd have to physically change your blood volume to change what a specific amount of alcohol would result in.

If you drink alcohol frequently you just metabolize more quickly than infrequent drinkers.
posted by treehorn+bunny at 7:26 PM on November 17, 2011 [2 favorites]

If my tolerance to alcohol increases, does my BAC go up more slowly?

posted by pompomtom at 8:37 PM on November 17, 2011 [1 favorite]

Keep in mind alcohol doesn't just stay there forever. The chart the CA DMV gives you shows how many drinks a person of a certain weight can have, but instructs you to subtract one drink for every two hours. If you go out to a bar, you usually don't go in, slam three shots, walk out and drive home (I hope).

So the longer the drinking session, the more you can drink without your BAC going too high. Of course this is unscientific, but given that stat came from state government, I bet it errs on the conservative side.
posted by drjimmy11 at 8:53 PM on November 17, 2011 [1 favorite]

Tolerance is a catch-all category for a complex combination of metabolic and cognitive adaptations. The short answer is that you cannot judge your BAC based on your subjective assessment of your intoxication. You also can't judge your actual impairment of things like reaction time based on a subjective assessment of whether you're "buzzed". Skip the last drink or if the numbers tell you your BAC should be borderline, spend an extra hour wherever drinking water. It is a very small cost for a very large risk.
posted by nanojath at 8:57 PM on November 17, 2011

Feeling Drunk and BAC often have very little to do with each other, as mentioned above. But you've already got the short answer, here's the long answer:

BARLAB at the University of Washington, like many labs as mentioned by slow graffiti, showed that much of our perception of alcohol is related to expectations - that is if you expect to get drunk, you're going to "feel" drunk, this placebo effect is well documented. I bring up UW because I used to live in the area and met one of the researchers, so stuff I don't have any citation for I'm just going to attribute to him.

But for a quick example on the clear difference between perception of impairment and BAC there's a neat Univ. of Connecticut study. For example, the perception of intoxication rises faster, and falls sooner than BAC - if you've ever blown a breathalyzer after waiting around trying to sober up, you know what I mean. There's also the phenomena of waking up after a night of drinking, not feeling drunk at all, trying to drive and realizing maybe you shouldn't be behind the wheel. It's not because being hungover makes you driving, but probably because your BAC is still elevated, even though you don't feel it.

(quick personal anecdote, after a bad break-up I drank myself into a sad little ball one night at a friends party. I slept on the sofa [actually I slept on three of her dinning room chair pushed together because I passed out when people were still using the sofa, awesome time, right?], woke up at ten, cleaned up the house, blew into one of those home breathalyzers, and still had a 0.12 even though I didn't feel drunk, at all. So I called a ride, chugged Gatorade and made emo Saturday afternoon phone calls to my friends once I got home - moral of the story, don't solve your problems with alcohol, its pathetic. Second moral, if you drank enough to black out you're drunker than you think the next day)

There's a lot of interesting details as well. For example, the longer you're drunk, the relative impairment to coordination at a given BAC improves, but you're higher brain functions (inhibition, judgement, spatial monitoring and short term memory) are still just as impaired. Pretty neat eh!? Hence, even though you feel sober, touch your nose and can walk a straight line, BAC is still the better tool to determine impairment (and the one Cops are going to use).

Now, to your question, tolerance in heavy drinkers is related changes in the brain, not to changes in the way your body deals with alcohol. For example, there was a 1997 paper in Science that pretty well described the way your brain deals with booze- essentially whatever booze does, your brain tries to do the opposite. So alcohol impairs pathways in the center of you brain that deal with physiological responses to emotions like anxiety. These pathways (called cAMP pathways) in a chronic drinker get ramped up. Receptors in the reward center of the brain (which, by the way, get activated by alcohol) get desensitized, so even though you're drinking the same amount, you're not going to feel as high or buzzed. These are long term changes but there are more short term changes in the hormones released when you expect to be drinking. While the short term effect of alcohol is to activate the inhibitory receptors in the brain (hence why alcohol is a depressant) when you build tolerance, your brain releases excitatory hormones (polyamines I think) to counter this effect. I'm not sure but I believe this is why alcoholics are able to handle much higher BACs (approaching 0.45 and 0.50) and stay awake while similar concentrations would kill me. . . or at least put me in a coma.

If you drink alcohol frequently you just metabolize more quickly than infrequent drinkers.

This is. . . true. . ., the more you drink pathways that metabolize alcohol are induced into action, but given how complex the interactions are that determine metabolism, I don't believe this has much effect on BAC curves. Given that alcohol is metabolized by zero order kinetics (meaning it almost always overwhelms liver metabolism capacity immediately and is metabolized at a constant rate regardless of concentration) and that ADH is not very inducible, and that's the enzyme responsible for 90% of metabolism in a non-alcoholic, changes in metabolism isn't going to have much effect on peak BAC. Once you're doing a lot of risky drinking (the drinking doctors say is terrible for you and increases your risk of alcoholism) maybe it drops a little faster, due to alternate pathways jumping in, but I doubt this is going to significantly change the effects alcohol has on the brain to produce intoxication (that is, you might be more sober in the morning, but it doesn't effect how drunk you are in the night).

In summary, you drank three long islands tonight? You drunk, girl, no matter how good you feel. Gimme your keys.
posted by midmarch snowman at 9:31 PM on November 17, 2011 [13 favorites]

Midmarch snowman gave excellent info...the same info I learned from a well know researcher who did research at BARLAB. One thing I wanted to add...after you have stooped drinking, your BAC decreases at a rate of approximately .015 per hour. Which is why people may still feel drunk the next morning...they actually are. Keep that in mind when figuring out how impaired you may be.
posted by MultiFaceted at 10:28 PM on November 17, 2011

Please note that I would never, ever drive if I felt buzzed. I am trying to be responsible, and figure out when it is both safe and legal to drive.

Just because it's legal doesn't mean it's safe. Someone at 0.08% which is perfectly legal in 47 of the lower 48 states (which in itself a stupifyingly high number to have as a BAC limit shared with only five other countries) is eleven times more likely to have a fatal accident than someone sober. Even if you test yourself before leaving alcohol could still be absorbed into your system raising your BAC as you drive. If you're DWI at the scene of an accident your insurance agency probably won't cover shit.

Don't gamble your livelihood or your life. The only safe amount of alcohol to drive with in your system is zero.
posted by Talez at 11:58 PM on November 17, 2011

If my tolerance to alcohol increases, does my BAC go up more slowly?


So, medically, what is "tolerance" then? One's ability to compensate for higher BAC? The body's ability the process the the alcohol so it goes down faster (while increasing at the same rate)?
posted by spaltavian at 8:41 AM on November 18, 2011

So, medically, what is "tolerance" then? One's ability to compensate for higher BAC? The body's ability the process the the alcohol so it goes down faster (while increasing at the same rate)?

Well, Drug Tolerance defined medically is: A person's reaction to a drug is changed with repeat exposure such that larger doses are required to achieve the same effect. So it could be due either to changes in the body's response to the drug (compensating for higher BAC) or the body's handling of the drug (making the BAC go down faster). To answer your question: In most drugs (alcohol, heroin, cocaine, benzos and so on) the tolerance we observe is likely almost all due to our body compensating better for higher 'doses' of the drug. Like MultiFaceted said, there isn't much change in the rate of BAC going down. I kinda remember that but I couldn't find it written down anywhere, other to what I alluded to with the rate of ADH metabolism not changing much in non alcoholics.

The rate you're body gets rid of alcohol is pretty standard. It is actually much more variable how quickly BAC rises, and I've read time to PEAK BAC time can easily vary from 30 to 120 minutes based on lean muscle mass, gender, what you've eating before drinking and other factors influencing gastric mobility. (I mentioned above that metabolism probably doesn't affect peak BAC, which I fear was misleading since peak is pretty variable, just probably not influenced as much by ADH metabolism of alcohol). Also one thing I want to add to clarify, you body CAN increase its ability to metabolize alcohol by recruiting alternate pathways, but this is typically seen in alcoholics. Though being alcoholic can also dramatically impair the ability to metabolize booze, as most of these pathways exist in the liver, and they don't work very well in an alcohol damaged or cirrhotic livers. Thus, assume you can metabolize .015% an hour (I've also heard this expressed as about 1 drink an hour, could be wrong) and avoid being an alcoholic. Seriously
posted by midmarch snowman at 12:43 PM on November 18, 2011 [1 favorite]

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