The Biology of Opioid Addiction

A person may not think twice about eating a poppy seed bagel until they may need a urine drug screen. Poppy seeds from poppy flowers are actually a common source of opium. However, poppy seed used in baking is typically a small amount. Opium poppy has been used throughout history for recreational and medicinal purposes such as pain relief and sleep (Drug Enforcement Administration Museum and Visitors Center, n.d.). The term opioid refers to natural, semi-synthetic, or synthetic chemicals that stimulate mu receptors found in the body. Opiates specifically refer to natural opioids. 

What are some examples?

  1. Natural Opioids: morphine, codeine
  2. Semi-Synthetic Opioids: oxycodone, hydrocodone, hydromorphone, oxymorphone, heroin
  3. Synthetic Opioids: methadone, tramadol, fentanyl

The opioid crisis refers to the three waves of increased opioid overdose related deaths since 1999. The first wave in the early 1990s resulted from the rise of prescription opioid. Then, increased usage of heroin led to a second wave in 2010. Finally, the popularity of synthetic opioids starting in 2013 caused the third and current wave of the opioid crisis (Centers for Disease Control and Prevention, 2020). 

Opioid addiction is due to various factors ranging from environmental influence to genetics. There have been many candidate gene studies on genes coding for the mu-opioid receptor (OPRM1), delta-opioid receptor (OPRD1), dopamine D2 receptor (DRD2) and brain derived neurotrophic factor (BDNF). Genome wide association studies is also at the forefront of identifying more genes that could be related to opioid addiction. Many of these studies have small sample size and inherent bias problems, but some of the results are promising (Crist et al., 2019). Twin studies have also suggested genetic variance or heritability in favor of opioid addiction, specifically, heroin. Opioid receptors involve the brain’s reward system while the dopaminergic system is associated with risk taking. Thus, the addiction cycle is tied into a complex relationship revolving around human behavior, physiologic responses and genetics (Wang et al., 2019). 

How to approach opioid addiction and overdose?

Naloxone is a mu-receptor antagonist used for the reversal of opioid overdose. While the introduction of Naloxone has saved many lives, there continues to be times where a person may not get the drug on time. For opioid use disorders, long-term addiction treatment is essential. Methadone, buprenorphine and extended-release naltrexone are currently used with psychosocial support to treat addiction (Volkow and Collins, 2017). There are many methadone clinics or SAMHSA-certified opioid programs throughout the United States that are both public and private. Methadone clinics provide a safe environment where a patient’s addiction can be managed through cognitive behavioral therapy, medication and medical detox. Patients are usually screened initially before given any medication. Once medication treatment begins, the doses given are individualized and periodically will require adjustments to ensure patient safety (American Addiction Centers Editorial Staff, 2021).

Need help or want to learn more:


American Addiction Centers Editorial Staff, 2. (2021, March 16). Opioid rehabilitation clinic – how does a methadone clinic work? Retrieved March 23, 2021, from

Centers for Disease Control and Prevention. (2020, March 19). Understanding the epidemic. Retrieved March 23, 2021, from

Crist, R. C., Reiner, B. C., & Berrettini, W. H. (2019). A review of opioid addiction genetics. Current Opinion in Psychology, 27, 31-35. doi:10.1016/j.copsyc.2018.07.014

Drug Enforcement Administration Museum and Visitors Center. (n.d.). Cannabis, coca, & Poppy: Nature’s ADDICTIVE PLANTS. Retrieved March 23, 2021, from

Volkow, N. D., & Collins, F. S. (2017). The role of science in addressing the opioid crisis. New England Journal of Medicine, 377(4), 391-394. doi:10.1056/nejmsr1706626

Wang, S., Chen, Y., Lee, C., & Cheng, C. (2019). Opioid addiction, genetic susceptibility, and medical treatments: A review. International Journal of Molecular Sciences, 20(17), 4294. doi:10.3390/ijms20174294

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