In this blog post, we’ll examine how opioid pain relievers are used to treat severe pain and how the risks of addiction and tolerance that can arise in the process are managed.
The foreign film ‘Requiem’ vividly depicts how a man and a woman trapped in drug addiction spiral toward a catastrophic end. Other movies and TV dramas also frequently portray lives shattered by drug addiction. Because drugs are perceived as substances capable of completely ruining a person’s life, it’s easy to assume—based solely on these depictions—that the lives of people who aren’t addicted are completely separate from drugs. However, there are instances where we use opioid medications for medical purposes. These are opioid analgesics, or opioid pain relievers. So why do we use opioid medications as pain relievers? Couldn’t using opioid analgesics lead to addiction? Let’s find the answers to these questions.
First, let’s look at the meaning of the term “narcotic.” In the general dictionary sense, “narcotic” is a collective term for substances that have anesthetic effects, are habit-forming, and can cause symptoms of addiction with long-term use. In the past, narcotics were often described as substances characterized by psychological dependence, physical dependence, tolerance, and social harm. However, in modern medicine, rather than lumping these concepts together under the single term “narcotics,” it is important to distinguish and understand the different types of drugs, their mechanisms of action, potential for dependence, and risks of misuse. Typical examples of narcotic analgesics include opiate-based drugs such as morphine and codeine, as well as various other synthetic and semi-synthetic opioids. While these drugs can cause harm to individuals and society if misused, they are used in medical settings as essential treatments for pain management. So why are these drugs used as analgesics in the first place?
Analgesics, as the term implies, are medications used to relieve pain. In medical practice, analgesics are categorized into non-narcotic analgesics and narcotic analgesics, also known as opioid analgesics. Typical examples of non-narcotic analgesics include acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs), which are selected based on the type and intensity of the pain. Unlike opioids, these medications do not primarily target opioid receptors in the central nervous system. Furthermore, some non-opioid analgesics exhibit a “ceiling effect,” meaning that beyond a certain dose, the analgesic effect no longer increases proportionally; thus, simply increasing the dose indefinitely does not make the pain relief stronger. On the other hand, when pain is very severe or cannot be adequately controlled with non-opioid analgesics alone, opioids—which provide a more potent analgesic effect—may be necessary. For this reason, opioid analgesics play a crucial role in treating moderate to severe pain, particularly cancer pain or severe pain occurring after surgery.
The reason opioid analgesics can provide such strong analgesic effects is not simply because they are inherently potent analgesics. As explained earlier, some non-opioid analgesics exhibit a ceiling effect, meaning their analgesic efficacy does not increase significantly beyond a certain dose. In contrast, opioid analgesics do not have a distinct analgesic ceiling effect in the same sense as non-opioid analgesics; therefore, if pain is not adequately controlled, the dose can be adjusted while monitoring the patient’s response and side effects. However, this does not mean that the dose can be increased indefinitely without regard for side effects. Since the risk of side effects—such as respiratory depression, drowsiness, nausea, and constipation—can increase as the opioid dose rises, the dose required for the patient must be determined with caution. Due to these characteristics, opioid analgesics are used not only for severe acute pain resulting from surgery or accidents but also for moderate-to-severe chronic pain caused by cancer.
Opioid analgesics are classified into weak and strong opioids. In the past, these were often described as “weak opioid analgesics” and “strong opioid analgesics.” Codeine is a representative example of a weak opioid. Codeine is also used as a cough suppressant, and part of it is converted into morphine in the body through the action of an enzyme called CYP2D6, thereby producing an analgesic effect. However, not everyone converts codeine into morphine to the same extent. Because the rate of codeine metabolism and the amount of morphine produced can vary depending on genetic characteristics, it is no longer appropriate to simply state, as was done in the past, that “approximately 10% of codeine is converted to morphine.” Particular caution is needed because some individuals metabolize codeine very rapidly, which can result in higher-than-expected morphine concentrations. Morphine is a representative example of a strong opioid. Morphine exhibits potent analgesic effects and is a representative opioid analgesic that has long been used to treat severe pain and cancer-related pain.
While opioid analgesics offer significant therapeutic benefits and have important clinical applications, their use can lead to problems such as tolerance, physical dependence, misuse, and addiction. Therefore, one should not assume that “using them for medical purposes will not lead to addiction.” While risks can be minimized by using the appropriate dosage under a doctor’s prescription and continuous monitoring, the risk of addiction does not disappear entirely. Furthermore, the development of tolerance does not necessarily imply addiction. Tolerance is the phenomenon where more medication is needed to achieve the same effect; physical dependence is a state in which withdrawal symptoms occur when the medication is suddenly discontinued; and addiction is a concept related to the loss of control over drug use and the repeated use of the drug despite harmful consequences. Therefore, when using opioid analgesics, the appropriate medication and dosage must be selected while continuously assessing the severity of pain and the patient’s condition. Specifically, for cancer pain, the World Health Organization (WHO) has proposed a “pain ladder” that recommends a stepwise approach based on pain severity: non-opioid analgesics, opioids for mild to moderate pain, and strong opioids for moderate to severe pain. However, in actual clinical practice, not every step is necessarily followed in sequence, as the patient’s pain level, cause, treatment goals, and potential side effects are comprehensively considered; if necessary, strong opioids may be used from the outset.
We have now reviewed opioid analgesics. While opioid analgesics can provide powerful pain relief for moderate to severe pain that is difficult to adequately control with non-opioid analgesics alone, issues such as tolerance, physical dependence, respiratory depression, misuse, and addiction must also be carefully considered. For this reason, healthcare providers assess the patient’s pain level and treatment goals, and adjust the opioid dosage and administration method while, if necessary, combining them with non-opioid analgesics or adjunctive therapies. In its guidelines for the treatment of cancer pain, the World Health Organization continues to recommend a three-step analgesic ladder based on pain intensity. Current pain management practices place significant emphasis not only on drug selection but also on the continuous assessment of the patient’s condition and the management of side effects and the risks associated with opioid use. While the discovery and advancement of opioid analgesics have enabled modern medicine to treat many patients suffering from severe pain due to surgery or serious illnesses, it has also placed us in a situation where we must address the problems of opioid misuse, dependence, and addiction. Going forward, efforts will likely be needed to develop new analgesics that provide potent pain relief while further reducing the risks of addiction and side effects, as well as to advance treatment methods that allow for the safe management of patients’ pain.
