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When buying pain killers in the pharmacy (no doctor prescription), sometimes I'm told to take the pain killers only after eating something, sometimes they say it doesn't matter, and most of the times they say nothing at all.

Is there a global recommendation about this? Should we eat before taking pain killers, or not? And more importantly, why should we consume painkillers on an empty stomach or vice versa? Many times when in pain, there's also no appetite so it's not trivial task to eat before taking them.

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    Isn't it a more interesting question to ask why one should eat something beforehand? The why would hopefully also answer under which circumstances... – Narusan Jun 11 '18 at 13:19
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    @Narusan good point. I trust you on this, please edit the question as you see fit. – Shadow The Princess Wizard Jun 11 '18 at 13:47
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    (Is there are global... → Is there a global...?) – Peter Mortensen Jun 11 '18 at 17:49
  • @PeterMortensen actually it should have been "Is there any global" and "any" became "are" somehow... but guess leaving it "a recommendation" is better. Thanks! :) – Shadow The Princess Wizard Jun 11 '18 at 18:50
  • Sounds like you're regularly going to a pharmacy to buy painkillers. That could be a serious warning that you are overusing them. Isn't there an alternative for you, instead of taking painkillers? – baao Jun 12 '18 at 11:30
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Ibuprofen and Aspirin are both non-steroidal anti-inflammatory drugs (NSAIDs). These NSAIDs can be differentiated into selective NSAIDs and non-selective NSAIDs.

Non-selective NSAIDs such as Ibuprofen and Aspirin are both COX-1 [Cyclooxygenase-1, also known as prostaglandin-endoperoxide synthase 1 (PTGS-1)] and COX-2 inhibitors [Cyclooxygenase-2 respectively]. (For the sake of completion: Selective NSAIDs only inhibit COX-2).

Both PTGS inhibitors prevent prostaglandin synthesis, which is a hormone amongst many other functions responsible for transmitting pain to the brain.

However, because a study from 2008 notes that COX-1 promotes the production of the natural mucus lining that protects the inner stomach and contributes to reduced acid secretion and reduced pepsin content, (and hence an inhibitor such as all non-selective NSAIDs will decrease said mucus), PTGS-1 inhibitors increase the risk of serious gastrointestinal bleeding and ulceration (and other stomach-upsetting symptoms).

Hence it is recommended to consume such non-selective NSAIDs with food, because this will allegedly lessen the symptoms.

It used to be "mandatory" to eat food before taking such medicine, but in 2015, the Australian Medicines Handbook has stepped back from this standpoint and now only encourages taking it with water and eating only if it does in fact upset one's stomach. A study published in 2007 has already found that the negative side-effects are dosage and time-dependent. Furthermore, a more recent study from 2015 found that the effect of food might not be as positive as expected.

So, this seems to be a pretty mixed bag. I find the solution of the Australian Medicines Handbook reasonable however: Don't take them with food unless you have gastrointestinal problems. If those problems should be severe, as always consult a physician.


Other common painkillers such as paracetamol that are not NSAIDs and thus not PTGS-1 inhibitors can be taken without food, as they are not stomach-upsetting.

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It is the information leaflet, which usually comes with all drugs, that should tell you to take them with or without food.


For one/few time use, it can be better to take them on an empty stomach or with water because they will pass through it quicker and will be absorbed quicker, so they will likely act quicker and stronger (PubMed Central).

Examples:


For the long-term use, it is better to take them with food to reduce the risk of stomach inflammation.

Examples:

  • Great finding, the PubMed study. But as both morphine and transform are prescriptive-only (for a very good reason due to respiratory depression and addiction), I think this answer would be better if excluding those as they should a) always be taken with doctors explicit instructions (ante and post cibum) and b) are not over-the-counter. – Narusan Jun 12 '18 at 15:23
  • Won't argue with that. – Jan Jun 12 '18 at 15:34
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It is indeed important to differentiate the drug in question and the individual and the intention for using the drug and the way it is taken, temporally.

Painkillers – or analgesics – come in a wide variety, be that in the form of opioids, cannabinoids, NSAIDs, ion-channel_modulators, myorelaxants or uncategorised drugs like ketamine. Not all are usually administered orally or even effective that way, by far not all are even available prescription free. As should become clear by now, "a general guideline" is almost impossible to formulate.

You have to inquire about one specific drug in question. And even then it will be complicated and our picture about every single one of all those drugs is still evolving and however detailed it may seem, incomplete. Follow the advice given on the leaflet, by your pharmacist and doctor.

Taking the example of cannabinoids, it is common knowledge that a full stomach will delay the effects of the active ingredients, but the simultaneous ingestion of a little bit of fat will increase the absorption of them. The more interesting molecules are all lipophilic and quite waste to digest in isolation.

It will be also a quite different story if we are talking about a one-time paracetamol administration or a long term course of aspirin, to name just one example pair.

The possible side-effects and interactions are different for each drug in question and each individual will fall on a different place of the scale of possible consequences. That does still not take into account the different foods that might interact with the drugs and the stomachs content.

Some important problems to keep an eye on when reading the accompanying leaflet are for example time the drug is in the stomach (gastric emptying) or the pH with the drug and with or with food (buffering).

Prostaglandins, NSAIDs, and Gastric Mucosal Protection: Why Doesn’t the Stomach Digest Itself? (Physiol Rev 88: 1547–1565, 2008; doi:10.1152/physrev.00004.2008.)

Since both other answers are basically correct on their own, I will only add some details that wouldn't fit into comments.

Concernig absorption rates: Absorption of acetylsalicylic acid from unbuffered and buffered gastric contents and Gastrointestinal Factors in Aspirin Absorption: A Quantitative Study but that is in contrast to Absorption of aspirin from the stomach in man, Influence of food on aspirin absorption from tablets and buffered solutions, Kinetics of aspirin absorption following oral administration of six aqueous solutions with different buffer capacities.

The most common side-effect of taking drugs orally is probably an upset stomach, but one of the more important effects might be actual bleeding, even with low dose aspirin: Risk of upper gastrointestinal bleeding associated with use of low-dose aspirin

While the already mentioned COX inhibition is a problem in itself, many natural substances occurring naturally in food are also known to exhibit this action, very probably increasing the risk if even ever so slightly. Substances that might act in this way:

Therefore, caution should be exercised if combining aspirin with any "natural" supplements with COX-2-inhibiting properties, such as garlic extracts, curcumin, bilberry, pine bark, ginkgo, fish oil, resveratrol, genistein, quercetin, resorcinol, and others.
Wikipedia: Aspirin

As a personal anecdote I might also add saffron to the list of side-effects enhancers.

But look how aspirin and paracetamol differ in their pharmocokinetics.

These factors would modulate the kinetics in the inflammatory focus, thereby prolonging the therapeutic action of the drug beyond that expected based on analysis of plasma pharmacokinetics. However, ion trapping also results in acidic compounds achieving high concentrations in the stomach wall and kidney, in which blockade of prostanoid synthesis causes the typical organ toxicity elicited by these compounds. Due to their lack of acidic structure, other COX inhibitors, such as dipyrone and paracetamol, are distributed homogenously throughout the body at therapeutic doses and induce analgesia, but induce no or very slight anti-inflammatory effects. This is partly due to their low concentration in inflamed tissues. (p14)

All NSAIDs approved by the US Food and Drug Administration carry the same boxed warning for cardiovascular and gastrointestinal risk. These state “NSAIDs may cause an increased risk of serious cardiovascular thrombotic events, myocardial infarction, and stroke, which can be fatal. This risk may increase with duration of use. Patients with cardiovascular disease or risk factors for cardiovascular disease may be at greater risk” and “NSAIDs cause an increased risk of serious gastrointestinal adverse events including bleeding, ulceration, and perforation of the stomach or intestines, which can be fatal. These events can occur at any time during use and without warning symptoms. Elderly patients are at greater risk for serious gastrointestinal events,” respectively. (p37/8)
Angel Lanas (Ed): "NSAIDs and Aspirin. Recent Advances and Implications for Clinical Management", Springer, 2016. DOI 10.1007/978-3-319-33889-7

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