Every time one takes a pill, drinks a glass of wine, or uses an illicit drug, it is understood that the effects are temporary. Caffeine only keeps one awake for a few hours, alcohol only intoxicates for a few hours, aspirin only staves off a headache for a few hours. This is because the immune system breaks medicines down, and when they're entirely gone, so is the effect.

So can the body break down anything?

The assumption is that the body remains alive long enough to finish breaking down (or not breaking down) the substance.

  • Please do not answer in comments. Commented Jul 9, 2015 at 5:54
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    I thought it was clear that it's the liver and kidneys, not the immune system, that deals with chemical compounds that are not wanted in the human body. And from the top of my head, lead and other heavy metals are known for remaining in the body instead of being properly removed. Commented Jun 9, 2016 at 14:00

4 Answers 4


Actually, in the case of most drugs, it has nothing to do with the immune system per se. Generally, drugs are either chemically modified (often in the liver) to make them inert, or excreted (either in the urine or the stool) thus removing them from the body. When the liver or the kidneys are not working properly, drugs fail to be excreted or digested, resulting in accumulation, which may be toxic.


Certainly not. By definition, it cannot break down poisons (at least not quickly enough) to stop the body being harmed or killed. In addition, it can not break down (or "neutralize") many radioactive substances. A famous example of this was the murder of Alexander Litvinenko:

On 1 November 2006, Litvinenko suddenly fell ill and was hospitalised. His illness was later attributed to poisoning with radionuclide polonium-210 after the Health Protection Agency found significant amounts of the rare and highly toxic element in his body.

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    Polonium-210 was more in line with what I was looking for. The assumption was that the body remains alive long enough to finish breaking down (or not breaking down) the substance Commented Mar 31, 2015 at 19:34

First of all, it's typically liver and the kidneys responsible for removing unwanted chemicals from the body, not the immune system. It should be noted that liver and kidneys have no "knowledge" which chemical is "bad" and which is "good". They have evolved to let some chemicals pass, react some chemicals etc. But there is plethora of compounds that had so little influence on evolutionary process, that we're not ready to handle them, since not being able to handle them was not selected against in the process of evolution.

So can the body break down anything?

tl;dr: No, there are many chemical compounds that are not handled by human body ideally and that, even if there's enough time for the body to handle them, still cause major harm.

Not sure what breaking down exactly means here, but certainly there are some compounds that can get stuck in the body, notably heavy metals. Those and some others accumulate in the body, possibly but not necessarily causing harm in the future. Let's have some examples:


Bioaccumulation is a process where organism (eg. you) absorbs certain chemical compound at faster rate than it excretes or processes it, which is probably what you meant by "breaking down". See bellow some examples of such accumulation. Remember that the compound to be accumulated doesn't need to be exactly toxic, but as the poison is in the dose, as long as you accumulate something, it eventually will became toxic, should it even be water.


Silver is a heavy metal and was used as disinfection in the first half of 20th century[1]. Silver accumulates in the human body, causing argyria. This often happens to people who adhere to so-called "alternative medicine", which includes promoting silver suspension as a cure to all kinds of diseases.[2]


Lead is more dangerous than silver and is recognised as important health problem by WHO.

Other examples

I will defer listing of other examples on wikipedia.


As I said in the introduction, evolution didn't prepare liver and kidneys for many chemicals. Sometimes the attempt to react them starts the toxic reaction itself and it would be better if the chemical stayed in blood as-is and was excreted in urine. Such event is a type of toxification, toxification can generally occur anywhere, not just liver.


Methanol is known as possible toxic component that can accidentally occur in alcoholic beverages. Methanol shares toxicity properties with ethanol, however on top of that, it is metabolized into formic acid in the liver. This is why, if there are no better alternatives, ethanol can be administered to prevent further methanol poisoning since it occupies the liver and therefore stops the toxification process. Bear in mind that this only works before the methanol was already turned into formic acid.[3]


Apart from accumulating, arsenic also is oxidated in body which produces much more toxic arsenic (III) oxide which is the famous deadly poison.



Any drug taken by mouth are being absorbed by the digestive system where a large amount may be destroyed by metabolic enzymes (first-pass metabolism) and enters the hepatic portal system. Then it's carried through the portal vein into the liver to be absorbed into the bloodstream and excrete the waste through bile. Some other bypass the liver, entering the blood directly. Only around 2-5% of the dose is excreted in an unchanged form in the urine.

The biological half-life of a substance refers to the body's cleansing through the function of kidneys and liver in addition to excretion functions to eliminate a substance from the body (time it takes for the blood plasma concentration of a substance to halve its steady-state).

Here are the common prescription medications which has its high half-life:

And here are the metals:

  • Mercury (as methylmercury) in the body has a half-life of about 65 days.
  • Lead in the blood has a half life of 28–36 days. In bone about 10 years.
  • Cadmium in bone about 30 years.
  • Plutonium in the liver about 40 years. Plutonium in bone about 100 years.

I hope that helps.

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    No, the body cannot "break down" everything - but if the liver and kidneys are working properly, it can excrete almost anything you throw at it, given enough time.
    – DrRandy
    Commented May 6, 2015 at 21:09
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    Your conclusion lacks any reliable sources. This is EXTREMELY dangerous because it means you're trying to build an answer from your own opinion instead of searching for one that already exists, backed by trials and empirical data. This creates the potential to SERIOUSLY MISLEAD those who read your response and conclusion. (Furthermore, you only cite wikipedia, which our community deems unreliable as a source for the answer's claim.)
    – Dave Liu
    Commented Feb 16, 2016 at 0:33
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    @kenorb can you give some example of claim what body can't excrete? - Many heavy metals, including lead. Although the body may excrete some or most of it, the rest of it can become incorporated into bone tissue and therefore can't be excreted. I'm sure there are other examples.
    – Carey Gregory
    Commented Feb 16, 2016 at 17:07
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    As for that replacing all the cells in 7 years thing, care to explain tattoos?
    – Carey Gregory
    Commented Feb 16, 2016 at 17:08
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    In addition to what Carey said, keep in mind that the new cells don't come out of nothing. They come from cell division of existing cells, with all the stuff that accumulated in those cells still in there.
    – YviDe
    Commented Feb 17, 2016 at 5:59

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