If the mechanism of action of paracetamol is unknown, why is it considered a safe drug to use for humans?


If the mechanism of action of paracetamol is unknown, why is it considered a safe drug to use for humans?

In: Biology

Because for a drug to be approved, it has to pass the clinical trial process. If the drug passes this process it can be approved. I would assume that during this process, the fever-reducing and pain-relieving properties showed improvements over placebo. I’d also assume that the rate of side effects was relatively low.

Ultimately it doesn’t matter *how* it works as long as it works and has no super unsafe side effects. The FDA has no requirement that you know how a drug works.

> Paracetamol has a central analgesic effect that is mediated through activation of descending serotonergic pathways. Debate exists about its primary site of action


We do know how it works, there’s just debate over which receptor site in particular it uses. Paracetamol is an old drug that’s been used for decades, we know all the side effects, we know what groups can take it and what groups can’t. If it were invented today would it pass regulators with this discrepancy? Probably but it would be harder and probably more tightly controlled and not sold in most shops. We still don’t know fully how anaesthetics and hypnotic drugs work. We just know that they do.


It works on the COX receptors, and the TRVP1 receptor: so in the same way as ibuprofen and cannabis. We do [know](https://en.wikipedia.org/wiki/Paracetamol) how and where it works.

For the same a surprising amount of medications are allowed to be sold, despite not knowing the exact mechanism of action; the have demonstrated efficacy, and aren’t harmful enough.

Drugs for depression have poorly understood mechanisms. We still don’t know how or why *ketamine* works, though we have some good ideas (NMDA, it’s thought, and the exact binding site was just recently resolved).

There is no requirement that we understand how a drug works in order to get approval. The testing that’s required is just for safety and efficacy. There’s no testing required that demonstrates how it works molecularly. There are a number of drugs that probably don’t work via their listed mechanisms at approval: eg, enbrel (actives th17 cells) and Avandia (cdk inhibitor).

Also, we can detect “toxicity” without necessarily knowing mechanism of action. As an extremely broad example, we can dose an animal for an extended period of time, look for deaths, tumors, cancers, changes in biomarkers of inflammation etc, etc and have a reasonable certainty of safety.

Paracetamol is NOT a safe drug ! It’s not considered as a safe drug by most doctors.

Paracetamol is only a quick solution to relieve some mild pain.

Studies, trials, and history of use. We don’t need to know how a medication works to see benefit from what the medication does, the FDA and FDA like bodies around the world use testing and trials to determine if a medication poses a risk to the general population. We know that in moderate doses it can cause damage to the liver, however due to its wide spread use, high efficacy and low risk of harm it’s deemed effective and safe.

Knowing how a drug works isn’t required for it to be approved/used. We’ve known for a long time that how we first thought SSRIs worked isn’t how they work. We’ve maybe finally, [this year](https://blogs.sciencemag.org/pipeline/archives/2021/02/19/how-antidepressants-work-at-last) got a real answer. [Here’s](https://blogs.sciencemag.org/pipeline/archives/2021/07/15/a-fifty-year-old-cancer-drug-doesnt-do-what-you-think) a 50 year old cancer drug that doesn’t do what people thought it did. (People knew for a while that we didn’t know how it worked, but we didn’t stop using it)

If paracetamol was invented today, it probably wouldn’t be approved, because it’s very easy to overdose and that’s not a justifiable risk for what it does. However, not knowing the exact mechanism of a drug is not a problem as long as safety is demonstrated.

The human body is immensely complex, and there are a large number of factors that can influence how a drug works in your body.

Theories are a good starting point for approaching drugs–but ultimately understanding how a drug might work, or understanding how it should work, just isn’t enough. At the moment, it’s beyond our ability to fully predict all the ways a drug might affect your body.

For concrete examples, consider Viagra and Latisse, medications for erectile dysfunction and eyelash growth respectively. Viagra was developed for high blood pressure and Latisse was developed for glaucoma. Their uses today are both unexpected side effects that were discovered during testing.

Because we can’t trust our predictions, we instead ask for evidence in the form of experiments. Once we have experiment data, it overshadows any theoretical knowledge. If a drug theoretically shouldn’t work, or we have no reason to believe it would work, but the data shows that it does, then we side with data and conclude that our theoretical understanding is limited. However, this is true even of drugs where our theoretical understanding is very good. We still recognize that our understanding is ultimately limited by our less-than-perfect understanding of the human body and this necessitates experimenting to look for unexpected effects. We also accept that the mechanism of action we believe to understand may only be one part of a more complex chain of mechanisms.

In short, when it comes to medicine: data trumps theory. This is true regardless of whether our theoretical understanding is weak or strong.

For those of us in the US, replace “paracetamol” with “acetaminophen” And if you don’t know what that is, replace that with “Tylenol”.

The biggest hurdle for any medicine is the test of time. Over the years paracetamol has seen countless tests so we exactly know what kind of effects can come out of it so as to treat it promptly.

There’s precautions to be taken and a dosage identified completely known to us, while the exact cogs ticking behind the scenes may not be fully be known we have a good data of how it affects everyone and hence treated as a over the shelf drug

Most medicine is like this. All we care about is what the side effects are. We don’t need to know how it works for it to be considered safe, we only need to know the results of taking it.

Billions have used it for decades. Well, for way longer even (read history on wikipedia).

That is the best way to find out something is safe. Not just drugs, but also cars, airplanes, and so on. There really shouldn’t be any surprises left to discover

Guess what. There are a LOT of drugs that we dont know why they work. But, they work.

Example. All of the anesthetic gases. There are a lot of theroes and partial answer as to how they work but the honest answer is, we dont know. But they do work and I use them every day.

when scientists/doctors say unknown, it means very differently than what a regular person thinks. for them it likely means they know 90 out of 100 things, and some extremely technical details are still not known. for a regular person unknown would mean they have absolutely no clue about it.