Firstly, it is to do with the way heroin is metabolised. There are two main ways that heroin is metabolised; one of the ways is through the Hepatic First Pass. This is done via the removal of an acetyl group when taken orally. The other way is through injections. Heroin that is administered via this route will evade the Hepatic First Pass and will quickly cross the blood-brain barrier. This is because of the presence of an acetyl group that makes it more soluble to fat. Once, in the brain, the acetyl group is removed, and heroin is reduced to 3-monoacetylmorphine and 6-monoacetylmorphine.
These compounds are reduced to morphine that then bind to opioid receptors that are found in the brain. Opioid receptors are important for autonomic processes of the body such as breathing, blood pressure, pain and arousal. When heroin binds to these receptors, it reduces pain, users of the drug also report a feeling of euphoria, dry mouth and a flush of the skin accompanied with a feeling of heavy extremities (Chetna J. Mistry, 2014). An individual can also develop tolerance to the drug, meaning more quantity of the drug may be needed to achieve the desired effect.
Research indicates that the presence of 6- MAM molecules in the blood after heroin has been reduced, could account for its high metabolism. There is also a noticeable difference in alleles among different ethnic groups. The study that was done on SNPs showed the variant Single nucleotide polymorphism A118G did not show altered binding affinities to most opioid receptors and alkaloids. However, the variant receptor A118G binds beta-endorphin and endogenous opioids that activate the Mu opioid receptors more tightly than the most common receptor (Bond, Gong & Kreek, 1998)
Also, beta-endorphins are more potent at the A118G variant than at the most common allelic forms; this is in the agonist-induced activation of the G proteins that have Potassium on their channels (Ying Zhang, 2005). The study concluded that the SNPs in the Mu receptor could alter the binding and signal transduction of the Mu receptors (Chetna J. Mistry, 2014). This may affect the normal physiology of the body, can impact on the treatment protocol, and can play a part in how individuals deal with diseases.
Studies have also found that there is a common reward pathway for drug addiction and that these addictions usually occur in individuals that are vulnerable both neurologically and genetically. This pathway is in the primitive limbic system. Opioids can affect this pathway by; increasing the postsynaptic sensitivity to dopamine or by increasing the release of dopamine by the neurons (Cherie et al., 1998).
Heroin is a very addictive drug in that, when injected or taken orally can mimic the body’s endorphin pathway of the CNS. The endorphins normally activate the bodies opioid receptors. These receptors are found at the surface of the cell membrane, in the Limbic system (controls pain, smell and hunger) where there are numerous. The receptors that heroin binds to influences whether the ion channels will open and, in some cases, influence the excitability of the neuron.
In addition to this, Heroin, also affect the GABA inhibitory receptors of the ventral tegmental area. When Heroin binds to these receptors, the amounts of GABA is reduced. In normal physiology, GABA reduces the amount of dopamine that is produced in the brain. Prolonged use of the drug will cause the reduction in cAMP. Cyclic AMP is one of the molecules that determine the ability of the neuron to produce electrical impulses; it has been found that the increase in these molecules is what causes cravings in heroin users (Guitart, Thompson, Mirante, Greenberg, & Nestler, 1992).
Effects on Adolescents
Studies have shown that prolonged use of the drug may cause structural changes to the brain by shrinking or enlarging some parts of the brain. For example, structural MRI has shown that prolonged use of the drug can cause changes to the prefrontal cortex of the brain. The images revealed that the prefrontal cortex had a lower proportion of the white matter, this is also seen in the brains of individuals with psychiatric abnormalities (Fowler, Volkow, Kassed, & Chang, 2007). These findings were correlated with the fact that individuals with these changes in the brain structure had a lower score in Wisconsin’s test. This is the area of the brain that controls logical thinking, goal setting and planning. This could explain why heroin users, which are mainly teenagers, are more likely to engage in high risk behaviours, are withdrawn from society and are aggressive.
Other signs of teenage drug addictions are; cognitive difficulties, short-term memory loss, a reduction in attention span, poor information processing and poor problem-solving skills compared to non-heroin or drug users. Some of the warning signs that a teenager is using drugs are; withdraw, low self-esteem, a sudden drop in the grades at school and when they suddenly start having older friends (Lambie, 2007).
Heroin and Pregnancy
Heroin is a lipophilic drug, hence the use of the drug in pregnancy can cause a wide range of effects, one of them is Neonatal Abstinence Syndrome (NAS). NAS is a syndrome where the foetus together with the mother become dependent on Heroin. The symptoms are; low birth weight, excessive crying, seizures, and irritability. Children that addicted to the drug also show reduced motor and behavioural developmental issues. They are also at risk of contracting hepatitis if the mother was sharing needles during pregnancy. Current treatment of heroin addiction during pregnancy is the use of methadone (Fajemirokun-Odudeyi et al., 2006). According to the Australian government of health and warfare, NAS is most likely to be found in young Australian women, unmarried and indigenous people (AIHW, 2006).
There a lot of factors that predisposes an individual to addiction. Recent studies have found that children from single-parent homes and teens that come from poor families are more likely to use drugs. Also, teens with poor relationships and with a family history of drug addictions are themselves more likely to suffer from drug addiction. Addiction can also be found in families that have no interest in education and in some cases if there is a history of any abuse, depression and anxiety (CDC, 2020). https://video.wordpress.com/embed/WbZJrztZ?hd=0&autoPlay=0&permalink=0&loop=0
AIHW. (2006). Statistics on drug use in Australia 2006. from http://www.aihw.gov.au/publication-detail/?id=6442467962
CHERIE BOND, K. S. L., MINGTING TIAN, DOROTHY MELIA, SHENGWEN ZHANG, LISA BORG,, JIANHUA GONG, J. S., JUDITH A. STRONG, SUZANNE M. LEAL, JAY A. TISCHFIELD,, & MARY JEANNE KREEK, A. L. Y. (1998). Single-nucleotide polymorphism in the human mu opioid receptor
gene alters b-endorphin binding and activity: Possible
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Fajemirokun-Odudeyi, O., Sinha, C., Tutty, S., Pairaudeau, P., Armstrong, D., Phillips, T., & Lindow, S. W. (2006). Pregnancy outcome in women who use opiates. European Journal of Obstetrics & Gynecology and Reproductive Biology, 126(2), 170-175. doi: http://dx.doi.org/10.1016/j.ejogrb.2005.08.010
Fowler, J. S., Volkow, N. D., Kassed, C. A., & Chang, L. (2007). Imaging the addicted human brain. Sci Pract Perspect, 3(2), 4-16.
Guitart, X., Thompson, M. A., Mirante, C. K., Greenberg, M. E., & Nestler, E. J. (1992). Regulation of Cyclic AMP Response Element-Binding Protein (CREB) Phosphorylation by Acute and Chronic Morphine in the Rat Locus Coeruleus. Journal of Neurochemistry, 58(3), 1168-1171. doi: 10.1111/j.1471-4159.1992.tb09377.x
Lambie, G. W., & Davis, K. M.,. (2007). Adolescent Heroin Abuse: Implications for the Consulting Professional School Counselor. Journal of Professional Counseling, Practice, Theory, & Research.
Megan Wood. (2004). Illicit drug use in australia from http://www.studnets.adelaisehs.sa.edu.au/subjects/issues/illictdrugs.pdf
Ying Zhang, D. W., Andrew D. Johnson, Audrey C. Papp and Wolfgang Sadée. (2005). Allelic Expression Imbalance of Human mu Opioid Receptor (OPRM1) Caused by Variant A118G*. Journal of biological chemistry.
CDC. (2020, April 30). Data and Statistics About Opioid Use During Pregnancy | CDC. Centers for Disease Control and Prevention. https://www.cdc.gov/pregnancy/opioids/data.html