How to decide which painkiller to take?

Question

This is a dilemma I find myself in every time I'm in need of a painkiller: should I take paracetamol (acetaminophen), ibuprofen or aspirin?

I've come across several articles outlining the differences (most notably one by NHS and one by NPS) and, while a good overview, they don't really provide a clear mechanism to make the decision.

Specifically, my understanding so far is:

• Aspirin and ibuprofen are NSAIDs and thus can be used to ease inflammation, unlike paracetamol

• Ibuprofen and paracetamol are similarly effective in treating pain, while aspirin may be less so (however, other sources claim paracetamol to be ineffective for some types of pain)

• Aspirin should never be taken by those under the age of 16

• In terms of adverse effects, ibuprofen may be a better option in comparison to paracetamol (according to this answer at least)

In many cases, different sources provide different, very often contradictory information, especially in terms of effectiveness and side-effects.

To make this question less broad, here are a couple of specific questions (all of these assuming the person in question has no allergies or an existing condition which may limit his options in this sense):

1. When should you not take a NSAID? It seems the fact they ease inflammation doesn't seem to make them less effective in any way.

2. Which is the most suitable to relieve symptoms of cold and flu?

3. Which is the most suitable to relieve pain caused by physical injury?

Answer 1

1. NSAIDs can increase the chance of heart attack or stroke. This risk may be greater if you have heart disease or risk factors (for example, smoking, high blood pressure, high cholesterol, diabetes) for heart disease. However, the risk may also be increased in people who do not have heart disease or those risk factors.

Heart problems caused by NSAIDs can happen within the first weeks of use, and may happen more frequently with higher doses or with long-term use.

NSAIDs should not be used right before or after heart bypass surgery.

NSAIDs may increase the chance of serious stomach and bowel side effects like ulcers and bleeding. This risk may be greater in older individuals. These side effects can occur without warning signs.

http://my.clevelandclinic.org/health/drugs_devices_supplements/hic_Non-Steroidal_Anti-Inflammatory_Medicines_NSAIDs

2. Acetaminophen is most suitable for relieving the symptoms of cold and flu. Acetaminophen affect the areas of your brain that control body temperature and pain. These medications can fight fevers and chills, ease headaches, and soothe sore throats and body aches. NSAIDs surpass paracetamol only when relieving the symptoms of fever.

http://www.webmd.com/allergies/sinus-nose-tool/treat-aches-pain-fever

3. Acetaminophen is the most suitable for relieving pain caused by physical injury than NSAIDs.

Acetaminophen works by inhibiting the synthesis of chemical messengers called prostaglandins, which help to transmit pain signals and induce fever. The body produces prostaglandins in response to an injury or illness. Acetaminophen reduces the pain by helping to block this signaling.

http://www.chemistryexplained.com/A-Ar/Acetaminophen.html

While NSAIDs work on a chemical level. They block the effects of special enzymes -- specifically Cox-1 and Cox-2 enzymes. These enzymes play a key role in making prostaglandins. By blocking the Cox enzymes, NSAIDs stop your body from making as many prostaglandins.

http://www.webmd.com/arthritis/features/pain-relief-how-nsaids-work#1