Otc Pain Relievers: Possible Interactions With Other Medicines

Over the counter pain relievers are some of the most commonly used medications around the world. These medicines are known to be relatively safe for general use, but are not fully free from the possibility of adverse drug interactions. Given the frequency with which these medicines are used, it is important that people using them are aware of this phenomenon.
OTC Pain Relievers: Possible Interactions with Other Medicines
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While using over the counter pain relievers, one must know that these medications can sometime interact with other medicines and lead to unintended pharmacological results. If you are using any other medicines you must know whether the OTC pain reliever you are planning to take interacts with your medicines or not. It may also be possible to avoid such interaction by appropriate selection of the pain reliever.


Interactions with other medicines and substances is one of the two major risks associated with over the counter pain relievers, the other being their unintentional side effects.

The common OTC pain relievers belong to

two groups of medicines. The first of them is Paracetamol or Acetaminophen (Tylenol), while the second group consists of non steroid anti inflammatory drugs (NSAIDs). The two groups bring pain relief by different mechanism, and have different interactions with other medicines.

1. Interactions of Acetaminophen or Paracetamol (Tylenol)

It relieves pain and fever without having much impact on inflammation (swelling). It relieves pain by two methods. First, it indirectly reduces prostaglandin synthesis, which are the chemical substances in the body for causing pain and swelling. In addition, it also acts by having a suppressant effect on the nerves, which carry pain.

Acetaminophen is a reasonably safe medicine and does not interfere much with the function of other medicines. However, it is metabolized by liver and hence any drugs that can effect liver function can interact with it. This is also the reason why it should not be taken with alcohol, as both are metabolized by liver and together can cause greater damage to liver. Thus all syrups and tonics which are based in alcohol can interact with acetaminophen.

Other medicines that can interact with acetaminophen include anti-epileptic medicines like Barbiturates and Phenytoin. Acetaminophen can cause liver enzyme stimulation that can reduce their impact causing epilepsy. On the other hand if liver function is impacted adversely, effect of these drugs may be increased leading to their toxicity. Another medicine which can interact with acetaminophen is the anti-Tubercular medicine Isoniazid (Nydrazid) which can also impact liver function.

Oral contraceptives can also interact with acetaminophen and that can become a problem in effective contraception apart from causing menstrual bleeding disturbances.

Other medicines which can also interact with acetaminophen are:

  • Cholestyramine (Questran), a bile acid sequestrant medicine used in for bringing down high cholesterol level
  • Warfarin (Coumadin), an anticoagulant medicine used in diseases caused by thrombosis, and after hear attacks
  • Zidovudine (Retrovir), a medicine for HIV and AIDS

Apart from the above, over the counter medicinal combinations containing NSAIDs or Acetaminophen should not be taken together with Acetaminophen as together their effect as well as side effects will get multiplied.

2. Interactions of Non Steroidal Anti Inflammatory Drugs (NSAIDs)

NSAIDs relieve pain, fever and swelling by inhibiting the synthesis of a substance called 'prostaglandins' which act as the mediator for pain swelling and fever. The prostaglandins are inhibited

by suppressing the enzymes- COX-1 and COX-2 which produce them in the body.
The common NSAIDs include Aspirin, Ibuprofen (Ibu-tab), Diclofenac (Cataflam) and Naproxen (Aleve). They interact with many medicines and modify their effect. Most of these interactions are common to all NSAIDs while a few of them are unique to the particular NSAID.

All NSAIDs interact strongly with each other. Thus if two or more OTC painkillers are taken together the chance of undesirable side effects like gastric bleeding or ulceration become very high. For this reason, multiple pain relievers should always be avoided.

All NSAIDs interact with Alcohol. If taken together they pose a serious danger of damage to the lining of the stomach resulting in swelling, bleeding or ulcers inside the stomach. If NSAIDs are frequently taken together with alcohol it can even lead to vomiting of blood.

Steroids used in allergic disorders or for auto-immune conditions lead to high acid levels in stomach and damage to its lining. When steroids and NSAIDs are taken together, they pose a high risk of stomach bleeding or ulcers.

Most NSAIDs also should be avoided when treatment with blood thinning agents like Warfarin (Dicoumarin) are being used because the bleeding that can be caused by NSAIDs can become very sever in cases of treatment with blood thinning agents, as after a heart attack, or thrombosis.

Most NSAIDs interact with following medicines:

  • the immuno-suppressants cyclosporine (Neoral) and methotrexate (Rheumatrex, Trexall)
  • anti depressant medicine lithium (Lithobid)
  • diuretics such as furosemide (Lasix)
  • steroids (prednisone and others)
  • anti hypertensive medicines enalapril (Vasotec) and lisinopril (Prinivil)

Any person who is already being administered any of the above medicines should either avoid OTC pain relievers in general and NSAIDs in particular, or take them only as per prescription of a medical specialist.

ASPIRIN also interacts with other medicines. Acetazolamide and ammonium cholride increase effect of Aspirin. Aspirin increases effects of many medicines like anti-diabetic drugs tolbutamide and chlorpropamide, the immuno-suppressant methotrexate, anti-epileptics phenytoin and valproic acid.

In case of over the counter drugs, possible interactions with other medicines should always be kept in mind while using them, as some of these interactions can at times become dangerous. For this reason alone, too many OTC medicines should be taken be due care. Awareness about all these aspects of OTC medicines helps in keeping these risks under control.
 



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