Why are Overdoses More Frequent with Opioids?

The opioid problem in the United States has officially reached epidemic proportions. Drug overdose is the leading cause of accidental death in this country, reports the American Society of Addiction Medicine, an opioid-related overdoses represent the vast majority of these deaths. This has led many people to wonder, “Why are overdoses more frequent with opioids?” The answer lies in the pharmacological properties of opioids as well as how they differ from other drugs.

Opioids Compared to Other Painkillers

Illustration of various types of drugs. Why are Overdoses More Frequent with Opioids?

Opioids are just one pharmaceutical pain management solution among many. Other over-the-counter painkillers can also reduce pain without having the elevated risk of overdose that comes with taking opioids. The reason for this lies in the pharmacological actions of these painkillers.

For example, acetaminophen (e.g., Tylenol) works by modulating neurotransmitters such as nitric oxide. Acetaminophen elevates the pain threshold, meaning that it takes a more painful stimulus to subjectively register as pain in your experience. Other common over-the-counter painkillers, such as ibuprofen (e.g., Advil) or aspirin (e.g., Bayer), act as non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs block the activity of inflammatory compounds that trigger the pain response. Thus, they are useful for reducing inflammation as well as exerting an analgesic effect.

Although these over-the-counter medications are effective in alleviating pain symptoms, they cause overdoses less frequently than opioids. This is because it takes a relatively high dose of aspirin or ibuprofen to cause an overdose. Acetaminophen overdose does occur and typically results in acute liver failure, but again, it takes a relatively high dose to trigger an overdose.

In contrast to the pharmacology of over-the-counter painkillers, opioid medications act on a class of opioid receptors in the brain that control the central nervous system response. Taking an opioid causes a strong parasympathetic nervous system response, characterized by slowed breathing, lower heart rate, and sedation. Because many prescription opioids are quite potent, even a relatively low dose can lead to a strong depression of central nervous system activity. Thus, respiration may slow to dangerous levels or cease entirely in an opioid overdose.

Opioids Compared to Other Central Nervous System Depressants

Opioids are not the only drugs that act as central nervous system depressants. Alcohol, benzodiazepines, and barbiturates also depress central nervous system activity. All of these drugs can lead to fatal overdose. For example, alcohol overdose often occurs when a person passes out and chokes on his or her own vomit.

Perhaps the most important reason that opioids are deadlier than other central nervous system depressants is that they are very prevalent and have a high addictive potential. Nearly 450,000 people sought treatment for opioid abuse in 2012, compared to 17,000 for benzodiazepines and 743 for barbiturates. The large number of prescriptions written for opioid painkillers means that many more people use these drugs on a frequent basis. As they become physically dependent on opioids, their risk of overdose increases.

Opioids Compared to Other Illicit Drugs

Finally, why are overdoses more frequent with opioids than with other illicit drugs? Again, the answer lies in pharmacology. The other most commonly abused illicit drugs include marijuana, cocaine, and methamphetamine. Marijuana has a very low potential for physical dependence and has resulted in very few documented cases of overdose. This is because the effects of marijuana include euphoria and increased appetite. Marijuana does not depress central nervous system activity like opioids, making it much less dangerous from a physical point of view.

Both cocaine and methamphetamine are central nervous system stimulants, meaning that they cause elevated heart rate, faster breathing, euphoria, and increased energy. Although both of these drugs are addictive and may cause overdose, they have different mechanisms of action than opioids. Cocaine and methamphetamine overdoses typically occur because of heart problems or stroke. Given how potent opioids are and how strongly they inhibit central nervous system activity, they remain the greatest contributor to drug overdoses in the United States.

Sources
Opioid Addiction 2016 Facts & Figures, American Society of Addiction Medicine. Retrieved on 05/02/2016.
Tylenol, RxList. Retrieved on 05/02/2016.
Alcohol Overdose: The Dangers of Drinking Too Much, National Institutes of Health. Retrieved on 05/02/2016.
Substance Abuse Rates by Drug, HealthGrove. Retrieved on 05/02/2016.
Methamphetamine overdose, U.S. National Library of Medicine. Retrieved on 05/02/2016.
How Drugs Can Kill, University or Utah Health Sciences. Retrieved on 05/02/2016.