# Any substances that are harmless alone, but when combined become fatal?
**URL:** https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031
**Category:** Factual Questions
**Created:** [February 18, 2015, 7:32pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031 "2015-02-18T19:32:41Z")
**Posts on this page:** 17
**Page:** 2
### Author:  [@Moriarty](https://boards.straightdope.com/u/Moriarty)
#### Post date: [February 19, 2015, 7:24pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/21 "2015-02-19T19:24:21Z")
[cherries and milk?](http://www.history.com/this-day-in-history/president-zachary-taylor-dies-unexpectedly)
---
### Author:  [@cmyk](https://boards.straightdope.com/u/cmyk)
#### Post date: [February 19, 2015, 7:53pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/22 "2015-02-19T19:53:34Z")
> [@Canadjun](#):
>
> See [Binary Chemical Weapon](http://en.wikipedia.org/wiki/Binary_chemical_weapon).
See: Die Hard With a Vengence. đ
---
### Author:  [@cmyk](https://boards.straightdope.com/u/cmyk)
#### Post date: [February 19, 2015, 7:57pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/23 "2015-02-19T19:57:45Z")
> [@Aspenglow](#):
>
> The one I always think of is Tylenol with alcohol. More than a few people have done in their livers with this seemingly harmless combination.
Just exactly how toxic is this combo? I mean, before it was well known as Not A Good Thing To Do, Iâm sure Iâve done it several times, and maybe even a few times since, and so far, all seems hunky-dory.
That said, Iâm sure itâs a toxic combo as warned, but it must take several often repeated occasions before your liver falls off and you die?
---
### Author:  [@buddy431](https://boards.straightdope.com/u/buddy431)
#### Post date: [February 19, 2015, 8:39pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/24 "2015-02-19T20:39:05Z")
> [@cmyk](#):
>
> Just exactly how toxic is this combo? I mean, before it was well known as Not A Good Thing To Do, Iâm sure Iâve done it several times, and maybe even a few times since, and so far, all seems hunky-dory.
>
> That said, Iâm sure itâs a toxic combo as warned, but it must take several often repeated occasions before your liver falls off and you die?
The trouble with paracetamol is that the therapeutic dose is close to the harmful dose. The current recommendations are to take no more than 4 g per day, while toxicity might commonly start around 10 g per day (depending on body weight and other factors). So if youâre taking near (or more than) the maximum daily recommended dose, youâre already skating on sort of thin ice, and anything that hurts your ability to safely metabolize it can make things a lot worse quickly.
Basically, when you drink moderately for several days, your liver ups the production of an enzyme that helps break down alcohol,but also breaks down paracetamol into a toxic byproduct (NAPQI). Usually only around 10% of paracetamol is converted to NAPQI, but if youâve been drinking moderately for several days, that fraction will increase.
So, say you have a drink with dinner, then get a headache. Youâre probably fine popping a couple Tylenol pills, because these are probably the first ones youâve had today, and you probably wonât be having a ton more before bed. The problem is not really the immediate proximity of alcohol and paracetamol, itâs the combination of a large amount of paracetamol after a several day period of drinking.
In fact, say youâve been drinking 4 drinks a day for the last week, you get a headache, decide to take some Tylenol. If you keep drinking like you have, youâre probably still OK, because the alcohol competes with paracetamol for the liver enzyme (though I wouldnât recommend trying it). The trouble comes when someone who usually drinks moderately comes down with the flu, feels awful, so both stops drinking and starts taking the maximum dose (or more) or Tylenol every day for a couple days.
[http://www.protectpatientsblog.com/2009/07/acetaminophen\_tylenol\_what\_is.html](http://www.protectpatientsblog.com/2009/07/acetaminophen_tylenol_what_is.html)
---
### Author:  [@Aspenglow](https://boards.straightdope.com/u/Aspenglow)
#### Post date: [February 19, 2015, 8:45pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/25 "2015-02-19T20:45:18Z")
Wow, that was a great explanation, **buddy431**. I never really understood the specifics until now â just knew the combination was a bad, bad thing to do.
I have a step mother who enjoys wine regularly and just had brain surgery to remove an aneurysm. She was sort of playing with the pain pill/alcohol combination because she misses drinking her wine. I just sent her your link. Thank you!
---
### Author:  [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)
#### Post date: [February 19, 2015, 9:21pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/26 "2015-02-19T21:21:54Z")
> [@nearwildheaven](#):
>
> Donât mix bleach and ammonia.
Isnât that the opposite? Chlorine is poisonous and ammonia certainly but I assume ammonium chloride would relatively benign.
---
### Author:  [@cmyk](https://boards.straightdope.com/u/cmyk)
#### Post date: [February 19, 2015, 9:50pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/27 "2015-02-19T21:50:43Z")
Agreed, that was a great breakdown buddy431!
Makes me feel better since Iâm not a moderate drinker (only every so often), nor do push taking acetaminophen past the recommended dose.
---
### Author:  [@fachverwirrt](https://boards.straightdope.com/u/fachverwirrt)
#### Post date: [February 19, 2015, 9:53pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/28 "2015-02-19T21:53:55Z")
> [@Hari\_Seldon](#):
>
> Isnât that the opposite? Chlorine is poisonous and ammonia certainly but I assume ammonium chloride would relatively benign.
You donât get ammonium chloride, you get chloramine vapors, which are highly toxic.
---
### Author:  [@Doug\_Bowe](https://boards.straightdope.com/u/Doug_Bowe)
#### Post date: [February 19, 2015, 9:56pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/29 "2015-02-19T21:56:27Z")
Back in the 50âs there were a number of high profile deaths when people took tranquilizers and later had a drink.
> **[Mixing Tranquilizers and Alcohol \[changed title\]](https://boards.straightdope.com/sdmb/showthread.php?t=173649)**
>
> Whatâs this business about mixing tranquilizers and alcohol? Does it really kill people? Is it a painful death? How much of each would need to be had? Moreover, would something like Benedryl work as a âtranquilizer?â Donât get me wrong; Iâm not...
---
### Author:  [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)
#### Post date: [February 19, 2015, 10:05pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/30 "2015-02-19T22:05:10Z")
> [@cmyk](#):
>
> Just exactly how toxic is this combo? I mean, before it was well known as Not A Good Thing To Do, Iâm sure Iâve done it several times, and maybe even a few times since, and so far, all seems hunky-dory.
>
> That said, Iâm sure itâs a toxic combo as warned, but it must take several often repeated occasions before your liver falls off and you die?
\*\*Buddy431âs \*\*explanation is excellent. I was not previously aware that stopping the drink could contribute to toxicity. Let that be a lesson to us all.
Iâd add that some people have a lower toxic threshold than others, just because (presumably genetic factors). Others may be more vulnerable due to baseline subclinical (that is, unknown) liver damage.
Lastly, acetominophen is included in a vast array of over the counter medications. So, to extend \*\*Buddyâs \*\*story: After a 4-day bender, you feel a bit hungover, so you take a few pills. The headacheâs pretty bad, so you take a few extra pills and lay off the sauce. Then you decide that itâs a cold after all, so you take a multi-symptom OTC remedy. You can get up to a pretty high dose quicker than youâd think.
---
### Author:  [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)
#### Post date: [February 19, 2015, 10:13pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/31 "2015-02-19T22:13:19Z")
Here is a link to a great âThis American Lifeâ episode about acetominophen toxicity. There was not much focus on the combination with alcohol (so therefore not so much on the OP topic).
> **[Use Only as Directed - This American Life](https://www.thisamericanlife.org/505/use-only-as-directed)**
>
> More than 150 Americans die each year on average after accidentally taking too much acetaminophen, the active ingredient in Tylenol.
---
### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [February 20, 2015, 3:00am UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/32 "2015-02-20T03:00:22Z")
Lead plus high speed can be hard on a body.
Weâve all heard of âhigh speed lead poisoningâ đ
---
### Author:  [@newcrasher](https://boards.straightdope.com/u/newcrasher)
#### Post date: [February 20, 2015, 3:36pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/33 "2015-02-20T15:36:36Z")
> [@DataX](#):
>
> Weâll ink cap mushrooms and alcohol?
>
> Neither one will kill you (although Iâm not sure the ink cap would be great on its own) - but drink some alcohol slightly after and you can die.
>
> Plenty of multiple drug interactions as well.
>
> Also MAOI with favs beans, sauerkraut, chianti, and a bunch of other stuff with tyromine can cause a hypotensive(or hyper - donât remember) crisis which you could theoretically die from.
So Hannibal was off his medsâŚ
---
### Author:  [@boffking](https://boards.straightdope.com/u/boffking)
#### Post date: [February 23, 2015, 6:27pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/34 "2015-02-23T18:27:04Z")
Iron oxide and aluminum make thermite.
---
### Author:  [@Ignotus](https://boards.straightdope.com/u/Ignotus)
#### Post date: [February 24, 2015, 12:09pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/35 "2015-02-24T12:09:56Z")
> [@](#):
>
> Iron oxide and aluminum make thermite.
They wonât self-ignite in your stomach though.
Glycerol and potassium permanganate might. (Glycerol is non-toxic; LD-50 for potassium permanganate is around 1g/kg body mass, so a spoonful likely wouldnât kill you on its own.) Together, they could start a nasty chemical fire in your belly, and probably also produce some toxic fumes of acrolein.
---
### Author:  [@CairoCarol](https://boards.straightdope.com/u/CairoCarol)
#### Post date: [February 26, 2015, 11:43am UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/36 "2015-02-26T11:43:13Z")
Grapefruit juice inhibits the effectiveness of some drugs. So I suppose if you took a live-saving drug but drank lots of grapefruit juice, you could run into trouble. But I donât know of any particular drug-juice combo that would be particularly dangerous.
---
### Author:  [@septimus](https://boards.straightdope.com/u/septimus)
#### Post date: [February 26, 2015, 12:43pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/37 "2015-02-26T12:43:09Z")
Itâs well known that the combination of Viagra and nitrates causes extreme low blood pressure or death.
Less well known is that nitrates and star gooseberry tea should not be mixed. I learned this myself. Feeling ill one evening I popped a nitro under-the-tongue, while my wife gave me a home remedy for headache. I stood up ⌠Wham! Blam! I lay down wondering if that was the end. My wife asked if I wanted more tea and I said Yeah. ⌠But rethought, realized the symptom was the same as Viaga+Nitro, asked for water instead. Googling I found cryptic references to star gooseberry and heart disease contraindication. Close call.
[Previous page](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031.md?page=1)