Revised by Kevin L. Zacharoff, MD December 2015
There are many different types of pain medications available to help healthcare providers treat patients with chronic pain. Depending on the specific medication, they can be obtained by prescription or are available over-the-counter (OTC). Pain medications provide an important component of most treatment plans intended to relieve suffering and enhance the quality of lives for many patients. As with most other medical treatments, they may also often have significant adverse effects. In some cases, especially with long-term use, a pain medication may cause more harm than good. For this reason, the risks of the decision to continue a certain medical therapy should always be weighed against its benefits, sometimes resulting in possible dose adjustments to minimize adverse effects, or in other cases discontinuation of the medicine altogether. This article reviews several classes of common pain medications and highlights some situations where long-term use may confound potential benefits.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are probably the most popular OTC pain medications. While some strengths are available by prescription, they are often easily obtained without a prescription. Some examples of commonly used NSAIDS are aspirin, ibuprofen, and naproxen. One of the key benefits of NSAIDs is that they are used to reduce both pain and inflammation. Most types of chronic pain are thought to have some degree of an inflammatory component.
Possible NSAID-related adverse effects from chronic use include stomach upset, exacerbation of gastric ulcers, renal function impairment, and increased risk of bleeding. Chronic use may also increase the likelihood of developing peripheral edema, likely due to sodium retention and/or renal effects. Some people have reported tinnitus (ringing in the ears) with long-term and excessive aspirin use. Usually NSAIDS can be abruptly discontinued without complications but in some cases chronic users may report a “rebound headache” when they suddenly stop. It is then necessary to gradually decrease the dose over time in order to completely stop the medication. A special class of NSAIDs called COX-2 inhibitors was developed with the intention of avoiding many of these adverse side effects. However, even this subset of NSAIDs has been implicated in increasing the risk of stroke and heart attack in high-risk patient populations with chronic use.
Acetaminophen is one of the most popular OTC pain medications that are commonly prescribed for mild to moderate pain. It is frequently used as an analgesic and antipyretic, and it is considered the first-line pain medication for many conditions, especially in people for whom NSAIDs are contraindicated. It is also often combined with other medications in prescription form including opioids like oxycodone or hydrocodone.
Irreversible hepatotoxicity is the biggest risk of chronically using large doses or overdose (intentional or unintentional) of acetaminophen. Unfortunately, unintentional overdose occurs frequently because patients are unaware of combining medications with each other that both contain acetaminophen. Signs and symptoms of liver damage can include abdominal pain, yellowing of the skin or eyes, and nausea or vomiting.
Opioid analgesics are available only by prescription. Examples of opioids are morphine, hydrocodone, oxycodone, oxymorphone, and codeine. Three common adverse effects of opioids are constipation, nausea and respiratory depression. Other potential adverse effects include cognitive impairment, urinary retention, itching, and swelling. Physiologic tolerance may result from chronic opioid use, requiring increased amounts of certain opioids to relieve pain. In some situations, this can ultimately result in loss of analgesic efficacy, and switching to another opioid molecule may be indicated (opioid rotation). Some postulate that long-term use of opioids can lead to a phenomenon known as “opioid induced hyperalgesia”. When this occurs, the person actually experiences increased sensitivity to painful stimuli. Another possible adverse effect associated with chronic opioid use is its effect on hormonal levels. Hormonal changes can cause decreased sex drive, tiredness, and changes in a woman’s menstrual cycle, and galactorrhea (secretion of breast milk in men or in women who are not breast feeding). Studies have shown that testosterone levels decrease in men and estrogen levels decrease in women receiving chronic high dose opioid therapy. Controversy continues to exist regarding the efficacy of long-term opioid analgesic therapy, with supporting and opposing arguments made on both sides of the debate. Certainly, most would agree that any good pain treatment plan should include opioid analgesics when deemed appropriate along with other medical and non-medical modalities.
Adjuvant analgesics are generally non-opioid medications used for pain relief which may be primarily used for other health problems, and they are usually prescribed with other pain medications. Two examples of adjuvant analgesics are anticonvulsants and antidepressants. They are generally used as part of a treatment plan for neuropathic pain. Adverse effects of these medications may include sedation and cognitive impairment and help with sleep. Another type of adjuvant analgesic that may be used is local anesthetic agents, such as topical lidocaine 5% for the treatment of post-herpetic neuralgia.
In summary, chronic use of pain medications, like chronic use of any other medications, can have a variety of adverse effects that can become greater when they are used regularly or over an extended period of time. It is important to stress to patients to only take those medications prescribed by a qualified healthcare practitioner, and to take them as they are directed to be taken. If medications are obtained over-the-counter, it is very important to read and follow the directions that come with them, no matter how harmless they may seem. Everything carries some degree of risk.
Of course, using medications inappropriately or in combination with other medications, including illicit street drugs, or alcohol, can result in particularly serious health consequences. It is important to review all medications and health problems with your chronic pain patients. Being informed about the specific adverse effects associated with pain medications can increase the chances of avoiding severe health problems, and lead to a better treatment outcome for their pain.