Drug Addiction Science:

Drug addiction is a very powerful syndrome involving both neurobiological and environmental influences. A series of reinforcing events, from initial changes in dopamine/reward systems to sensory drug-cue perceptions, causes the user to perpetually abuse the addictive drug; often, biochemical and psychological dependence is formed. They are further troubled by intense impulsions to take the drug – cravings. They have varied manifestation in drug addicts, even those who have abstained from the substance for an extended period time, in terms of personal experience, duration, and degree of irritability. Yet, it is evident that the body has changed its responses to certain stimuli, including the drug and other substances, events, and activities (see Goldstein & Volkow, 2002 for a review).

The brain is a dynamic organ susceptible to the poisons we ingest, inhale, or otherwise intake. The neurobiology of drug addiction is strong, compelling, and undeniable; despite restrictive laws, millions of people continue to abuse illegal substances. Changes to a drug addict's neurotransmitter systems, predominantly the dopamine-reward mechanism by way of potent psychotropic compounds, displace his cognitive perception to favor its use by classical conditioning. Cues related to the drug (i.e. drug paraphernalia, drug dealers, other substances) trigger a cognitive-biochemical cascade that impels the addict to yearn for the substance. Moreover, disturbance in thought processing may cloud the individual's judgments to prefer immediate euphoric benefits over long-term hazards. Other activities may have reduced hedonic potential pressuring the addict to take the drug to feel "normal."

Cocaine, cannabis, nicotine, and alcohol addiction are the most common substance disorders and share an important neurobiological feature; they all increase dopamine neurotransmission (Carlson, 2004). However, each substance has a different site of action, behavioral manifestation, degree of dependence, and cessation profile. Though cocaine reaches the brain rapidly and has strong behavioral consequences, "soft" drugs such as nicotine and alcohol harm users in record numbers, are addictive, and may have greater costs to society.

Cocaine blocks the reuptake of dopamine from terminal buttons, whereas cannabis, nicotine, and alcohol stimulate the release of dopamine in the nucleus accumbens and other mesolimbic regions. Cocaine users feel euphoria and are more open to social interactions and abusers may experience psychotic symptoms. Cocaine uniquely does not produce tolerance; on the contrary, it has the potential for sensitization. Withdrawal may involve unpleasant emotions and even anhedonia. Aside from dopamine related pleasure effects, THC, the active ingredient in cannabis, inhibits GABAergic neurons causing short term memory problems. Nicotine directs the release of ACh, a neurotransmitter involved in the autonomic nervous system that innervates muscles (including the heart and arterial fibers) and glands. Smoking cessation may cause anxiety, insomnia, and concentration difficulties. Alcohol produces both mild euphoria and anxiolytic effects, the latter contributing to negative reinforcement for alcohol may temporarily relieve anxiety. Further, alcohol triggers brain cell death by acting as a GABAA agonist and indirect NMDA antagonist.

Compulsive cigarette smoking and coffee use triggers several damaging events to the cardiovascular system; however, these two very dangerous addictions are often concurrently abused. The two most common psychostimulant drugs used throughout the world, nicotine and caffeine, reciprocally enhance their stimulation profiles, however, their opposing affects may serve as the key to their co-dependence. By blocking adenosine receptors, caffeine generally enhances feelings of excitation (motivation, alertness, vigilance), confidence, and well-being. On the contrary, nicotine acts on nicotinic ACh receptors to generate pleasure and relaxation. Perhaps, the body, in seek of a homeostatic balance, seeks a divergent drug – one that counters the affects of other. In addition, individual and mutual metabolic and other pharmacokinetic characteristics may synergistically strengthen their effects. Moreover, studies suggest that both drugs enhance dopaminergic neurotransmission (Gasior et al., 2002), further reinforcing their intake.

Further study into drug addiction, cravings, and concurrence will help devise interventions to reduce relapses and end drug dependence. Given the high prevalence for concurrent abuse and potential for relapse, studies involving overlapping addictions will benefit addiction recovery programs. A combinatory approach of anti-craving drugs (i.e. naloxone) and cognitive behavioral therapy in accordance to the biopsychosocial model may effectively prevent relapses and promote recovery from addiction – a multidimensional syndrome.

References

Carlson, N. R. (2004). Chapter 18: Drug Abuse. In Physiology of Behavior (pp. 572 600). Boston: Allyn & Bacon.

Gasior, M., Jaszyna, M., Munzar, P., Witkin, J. M., & Goldberg, S. R. (2002). Caffeine potentiates the discriminative stimulus effects of nicotine in rats. Psychopharmacology, 162(4), 385 395. Retrieved January 6, 2005, from PubMed database (12172692).

Goldstein, R. Z., & Volkow, N. D. (2002, October). Drug Addiction and Its Underlying Neurobiological Basis: Neuroimaging Evidence for the Involvement of the Frontal Cortex. American Journal of Psychiatry, 159, 1642 1652. Retrieved from ProQuest database.

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