According to the government, opioids are considered a Schedule II drug (DEA, 2025). The reason for opioids’ classification as Schedule II rather than Schedule I is that there is an acceptable medical practice for Schedule II drugs, such as opioids, which are commonly prescribed as a pain killer. However, Schedule II also implies a heavy possibility for abuse (DEA, 2025). With this in mind, the typical users of opioids are those who have undergone painful life situations or surgeries.

There are numerous routes of administration for opioids, such as being injected, snorted, sniffed, smoked, swallowed orally in the form of a pill or tablet, or administered subdermally through patches (DEA, 2022). The effects of some opioids, like fentanyl, start much quicker than most other opioids (NIDA, 2021). According to research done by Prommer and Thompson, intranasal fentanyl absorption can take up to 30 minutes, which is significantly faster than taking the drug by oral routes (Prommer & Thompson, 2011). Moreover, an increase in body temperature can lead to greater absorption rates (Prommer & Thompson, 2011).

Opioids work by binding to the opioid receptors in the brain, located throughout the central nervous system (ADAMHS, n.d.). An experiment was performed by Alzu’bi and colleagues on mice to determine the effects of chronic fentanyl usage. According to this experiment, there was a link between fentanyl usage and white matter injury, as well as abnormal myelin sheath formation (Alzu’bi et al., 2024). Myelin in the brain is important, as it coats the axon within neurons, allowing for action potentials to occur more quickly. Furthermore, this same study shows chronic fentanyl usage can lead to a damaged cerebral cortex, which they assume could explain why there is a volume decrease in those with long-term opioid use (Alzu’bi et al., 2024).

According to Carl Hart and Charles Ksir, it is found that endorphins have potent opioid effects (Hart & Ksir, 2021, p. 318). There are three main opioid receptors in the brain, mu, kappa, and delta, which play a role in the determination of pain in the body, with delta being the main receptor for chronic pain (Hart & Ksir, 2021, p. 318). However, opioids are considered agonists, antagonists, or partial agonists, depending on the type of drug (Pathan & Williams, 2012). For example, naloxone, commonly known as Narcan, is an opioid antagonist due to its binding of the receptors and produces no response, while not allowing an agonist to bind to the receptor (Pathan & Williams, 2012). This is why Narcan is used to help those suffering from an opioid overdose. Though, due to the complexity of the brain and neurological connection, it is not entirely understood how opioids reduce pain (Hart & Ksir, 2021, p. 318). Furthermore, endorphins are released by the pituitary gland and enkephalins are released from the adrenal gland; due to these peptides already circulating through the body, it is harder to understand what is affecting the perception of pain (Hart & Ksir, 2021, p. 318). Lastly, it is unknown whether actions that release more of these peptides, such as exercise, alter the brain’s reaction to these substances (Hart & Ksir, 2021, p. 318).

According to a study done by Karabulut and colleagues, they found that those in the Opioid Use Disorder group reported higher rates of impulsiveness and aggression compared to the healthy controls (Karabulut et al., 2025). Hart and Ksir also expand upon the subjective effects of opioids, with many early clinicians viewing the medical effects for pain relief as positive (Hart & Ksir, 2021, p. 305). Furthermore, old English writers would also use opioids to help with their writing; though many also wrote about their favorable view toward opioids (Hart & Ksir, 2021, p. 305).

The main behavioral effect of taking opioids is a lack of movement, due to the body’s system being depressed (Hart & Ksir, 2021, p. 322). Opioids depress the system, meaning they slow everything down. Due to this, those who use opioids, like morphine or heroin, tend to sleep because of the depression to the system (Hart & Ksir, 2021, p. 322). Moreover, it is reported that those under the influence of opioids are less likely to be “active” or “alert” compared to their usual behavior (Hart & Ksir, 2021, p. 322). According to the DEA, fentanyl specifically also causes confusion, pain relief, urinary retention, respiratory depression, and pupillary constriction (DEA, 2022).

With opioid tolerance comes a constant need to increase the dosage as time passes (Hart & Ksir, 2021, p. 319). Fentanyl withdrawal, for example, comes with a myriad of symptoms, such as “nausea and vomiting with diarrhea, aches, pains, and a general sense of misery.” Furthermore, pupil dilation, goose bumps, tremors, hot and cold flashes, loss of appetite, insomnia, and raised blood pressure are also possible during withdrawal (Hart & Ksir, 2021, p. 320). These extremely uncomfortable withdrawal symptoms make it difficult for many to withdraw from opioid use.

When it comes to individuals using an illicit drug, such as opioids, there are always going to be risks. “The opioid trio: coma, depressed respiration, and pinpoint pupils” is a common way to determine opioid overdose (Hart & Ksir, 2021, p. 322). Due to opioids causing the respiratory system to slow down, opioids are considered one of the top drugs that cause an overdose (Hart & Ksir, 2021, p. 322). Furthermore, many of those who do overdose, mostly on heroin, tend to also have high blood alcohol levels, and it is theorized the death is due to the opioid and alcohol interacting (Hart & Ksir, 2021, p. 322). Some short-term risks of using opioids include nausea, vomiting, or constipation, due to the gastrointestinal tract slowing down the small intestines and the colon (Hart & Ksir, 2021, p. 322).

While opioids are still a dangerous drug, there are some medical uses for them. One such use is as a cough suppressant (Hart & Ksir, 2021, p. 319). According to Hart and Ksir, opioids have a cough-suppressing quality and are taken when coughing is unproductive, meaning it does not clear the airways or remove phlegm from the lungs (Hart & Ksir, 2021, p. 319). The most common use of opioids is pain relief. Opioids reportedly have an effect in diminishing a patient’s awareness of their own aversive stimulus (Hart & Ksir, 2021, p. 319). Moreover, opioids do not put a patient into a deep slumber, making it easier to awaken someone readily, if need be (Hart & Ksir, 2021, p. 319).

Many people draw their understanding of opioids from mass media, whether it is television, magazines, movies, or conversations. For a TV show, such as Grey’s Anatomy, it is more beneficial to have drama surrounding drug use. However, Hart and Ksir argue this is not always the case. First, they dispel the major notion that those who inject opioids, such as heroin, are immediately hit with a session of euphoria (Hart & Ksir, 2021, p. 321). Most individuals will experience nausea and discomfort after large doses; though this takes place, many users will continue to push through until they receive the euphoric feeling (Hart & Ksir, 2021, p. 321).

The media portrays withdrawal symptoms as excruciating, akin to dying (Hart & Ksir, 2021, p. 322). However, Hart and Ksir combat this narrative, stating it simply depends on the person, and for many users, withdrawal feels like catching a virus (Hart & Ksir, 2021, p. 322). Moreover, the most common misconception is that taking an opioid once gets a person hooked forever. While opioid addiction is of concern, Hart and Ksir reveal that most users don’t become addicted, with “less than one-third of heroin users and less than one-tenth of people prescribed opioids...meet the criteria for...opioid use disorder” (Hart & Ksir, 2021, p. 322).

• ADAMHS Board of Cuyahoga County. (n.d.). Facts about fentanyl.
• Alzu’bi, A., Baker, W. B., Al-Trad, B., Zoubi, M. S. A., AbuAlArjah, M. I., Abu-El-Rub, E., Tahat, L., Helaly, A. M., Ghorab, D. S., El-Huneidi, W., & Al-Zoubi, R. M. (2024). The impact of chronic fentanyl administration on the cerebral cortex in mice: Molecular and histological effects. Brain Research Bulletin, 209(209), 110917.
• Drug Enforcement Administration. (2022, October). Fentanyl.
• Drug Enforcement Administration. (2025). Drug scheduling.
• Hart, C. L., & Ksir, C. J. (2021). Drugs, society & human behavior (18th ed.). McGraw-Hill Education.
• Johns Hopkins Medicine. (2022, October 19). Opioids.
• Karabulut, S., Erdoğan, A., Kuloğlu, Z., Düzgün, M., & Kulaksızoğlu, B. (2025). Impulsivity and aggression in patients with methamphetamine use disorder and opioid use disorder. Journal of Substance Use, 1–5.
• National Institute on Drug Abuse. (2021, December 21). Fentanyl.
• Pathan, H., & Williams, J. (2012). Basic opioid pharmacology: An update. British Journal of Pain, 6(1), 11–16.
• Prommer, E., & Thompson, L. (2011). Intranasal fentanyl for pain control: Current status with a focus on patient considerations. Patient Preference and Adherence, 157.