Addiction has classically been defined as the excessive use of a harmful drug despite its consequences, along with the inability to stop at will. This occurs when an individual’s desire for the short-term positive effects of the drug outweighs the consequences of its long-term negative effects . Prolonged use of many drugs causes dependence – a condition during which the cessation of drug-use will elicit unpleasant, and often dangerous effects . This is when the individual is converted from ‘wanting’ the drug’s psychoactive effects, to ‘needing’ it in order to avoid harmful withdrawal symptoms.
Individuals may use these drugs with increasing frequency in order to continue experiencing their positive effects, a behaviour which often becomes compulsive, and prevents the individual from limiting its use to a safe level. After prolonged use, as discussed above, drug dependence develops. The World Health Organisation describes this as a psychobiological state whereby compulsive drug consumption results in negative consequences during its absence . This describes a state where the body adapts to the regular consumption of the drug – for example, as nicotine increases the firing of the mesolimbic pathway, the stimulation of GABAergic inhibitory neurons becomes increased in order to compensate. This produces tolerance, which means that the individual will need to take increasing doses of the drug in order to maintain the same response as produced initially. However, if the individual ceases to consume nicotine, the mesolimbic stimulation is removed, but the increased firing rate of the GABAergic inhibitory neurons remains. This means that the stimulation of the mesolimbic pathway will be even lower than it was originally, therefore producing the opposite effects of the drug, as well as other effects resulting from low mesolimbic activity (withdrawal symptoms) . This is the process of drug dependence, and explains how individuals can quickly go from ‘wanting’ to ‘needing’ to consume a drug.
Although the mechanisms regarding how addiction occurs are relatively clear, the reasons why some individuals are more prone to it are less well-understood. One of the most significant risk factors, however, is genetic predisposition. This has been proven by various twin studies, all showing that identical twins are more likely to develop an addiction if their twin has, than non-identical twins, thus confirming the role of genetics in addiction . Addiction is believed to be a polygenic state and many of the genes which contribute to the likelihood of developing an addiction have been reported. For example, polymorphisms in the gene which codes for D2 receptors have been shown to increase an individual’s chance of developing an addiction .
Although the classical definition of addiction only refers to substance abuse, a more modern view is that compulsive use of pornography, gambling or shopping, for example, should also be classed as addictions – ‘behavioural addictions’. Although the primary effects of substance addiction and behavioural addiction are blatantly different – behavioural addiction will not, of course, produce the same risks of infection or overdose as substance addiction might – however, they do share many similarities, particularly in their aetiologies.
Although it is commonly believed that behavioural addiction does not produce withdrawal symptoms, this is not strictly true. Withdrawal symptoms which are produced by decreased firing of dopaminergic neurons in the mesolimbic pathway are similar in both substance and behavioural addiction. These mainly include emotional symptoms, such as irritability, anxiety and low mood .
When an individual ‘needs’ an experience that they used to simply ‘want’, then an addiction is present whether the experience is drug-use, shopping, sex, or anything else.
Chas Alexander Smith
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