The term 'addiction' derives from the Latin word 'addicere', to sentence . Thus, someone who has an addiction has been locked to a term of involuntary service to that habit that has them in its thrall.
It is a conditioned response that is reinforced by repeated administration of a natural or synthetic substance. This causes the individual to develop both a physical and psychological dependence to that substance.
What is addiction?
Physical addiction is a state in which the body has adjusted itself to the substance in such a way that it has now become part of the 'normal' functioning of the body's tissues. This is defined by two characteristics:
- Tolerance: This is manifested by a decreased physical sensitivity to the substance caused by a continuous exposure. This means that larger doses of the substance need to be administered to achieve the same physical effect. Eventually, these increases will reach a plateau.
- Withdrawal: This describes the unpleasant physical and psychological effects experienced on cessation of using the substance to which the body has become accustomed. The symptoms depend on the particular substance used, and are primarily the opposite of the effects of the drug itself. They can include intense craving for the substance, anxiety, irritability, nausea, headache, tremor and hallucinations.
Psychological addiction is the state in which an individual feels a compulsion to use a substance for the pleasant sensation that it produces, without necessarily being physically dependent on it. They may rely heavily on this substance to feel good and may orientate their activities to obtaining and using it. The repeated use of this substance may lead to them depending on it to get through their days.
There are substances that are physically addictive without being psychologically addictive, such as the anti-depressant venlafaxine. Patients who forget to take their regular daily dose will start to experience nasty flu-like symptoms relatively quickly. However, they do not feel a psychological urge to take the drug. The opposite of this is cocaine. Regular cocaine users do not show the usual symptoms of physical dependence, i.e. tolerance and physical symptoms of withdrawal. However, it is very addictive psychologically, more so than heroin. In the past, a pre-occupation with the importance of physical drug dependence led to a pronouncement by experts that cocaine was a relatively innocuous drug. Sigmund Freud himself was a big fan, prescribing it as a cure-all for all manner of complaints. People often pay more attention to physical factors than psychological ones, as they are considered more real. However, it is the psychological aspects of addiction that are the most important in understanding the nature of dependence.
Neurological basis of addiction
In Western society, the three most commonly used non-therapeutic drugs are caffeine, nicotine and ethanol. These are legal and freely available, unlike a large number of other drugs that human beings consume. Common illegally used drugs include opiates (morphine, heroin), anxiolytics (diazepam, temazepam), psychomotor stimulants (amphetamines, cocaine) and psychomimetic agents (LSD, mescaline, cannabis). This is an extremely diverse group of chemicals with little in common at the molecular and cellular level. What links them is that people experience a pleasurable (hedonic) effect from taking them, and often want to repeat this.
This is because of the activation of mesolimbic dopaminergic neurones. These are nerve fibres that project from the midbrain to parts of the limbic system and frontal lobe of the brain, and use dopamine as a neurotransmitter. This is the brain's 'reward pathway', and plays a very important part in motivating behaviours like feeding, sex and drug taking. Activation of this pathway increases an animal's desire to experience a hedonic stimulus, without actually increasing the pleasurable effect of the hedonic stimulus. The normal function of this neural pathway is to encourage behaviours that maintain the body's homeostasis and encourage reproduction. Thus, a hungry animal activates the pathway when it eats food and a thirsty one when it drinks water. This means that when the animal is next thirsty, it desires to repeat the same behaviour that quenched the thirst last time, i.e. drink some water from the river. Studies have shown that addictive substances or behaviours act either to stimulate the release of dopamine or to enhance its actions within this neural network. This causes a strong reinforcement of those behaviours that have potentiated the normal action of dopamine.
Chronic over-stimulation of this pathway eventually causes the system to be down regulated, leading to the phenomenon of tolerance. This is where more and more of the drug needs to be administered to achieve the required effect in terms of psychological reward. If the drug taking activity is stopped all together, there is a marked decrease in the release of dopamine, leading to the powerful psychological withdrawal symptom of craving.
Substance abuse
Addiction does not necessarily indicate abuse. Whether or not a person is abusing, or overusing, a drug depends on the extent and the impact of the use. A psychiatrist would diagnose substance abuse or drug dependence based on two criteria (Davidson, Neale, 1994) .
- The person shows a clear and persistent pattern of pathological use, e.g. heavy daily use, inability to stop or decrease amount used.
- The abuse has produced at least one of the following problems:
- Failing to fulfil important obligations, e.g. repeatedly neglecting a child or being absent from work.
- Putting oneself or others at risk for physical injury or illness, e.g. driving whilst intoxicated, liver cirrhosis due to alcohol abuse
- Having legal difficulties, e.g. being arrested for disorderly conduct
- Having serious social or interpersonal problems, e.g. repeated arguments with family or co-workers (Sarafino, 1998)
Drug dependence describes any behaviour where the drug taking becomes compulsive and takes precedence over other needs. It implies a state of physical dependence on the substance, as well as psychological dependence. Drug abuse or substance abuse are less specific terms, and can be taken to mean the recurrent use of any drug that is harmful to the individual, including drugs in sports. It does not imply a state of physical or psychological dependence, although these may be present (Rang et al, 2003).
Behavioural mechanisms in addiction
There are several behavioural mechanisms that lead to the development of drug dependence. Positive reinforcement is a term used to describe the encouragement of a certain behaviour pattern that results in a pleasurable outcome each time the behaviour is completed, resulting in activation of the mesolimbic dopaminergic neurones. So, if the drug is injected or inhaled, the person comes to associate those actions with the pleasurable feelings that result. For instance, heroin users have a very strong association between self-injection and feeling a sudden euphoria seconds later. This association has been manipulated in detox therapy. If the craving for a hit is sufficiently strong enough that an addict would want to 'fall off the wagon', they are encouraged to self-inject a small amount of saline solution which they have prepared the same way that they would prepare a hit. This often has the effect of immediately dulling the craving for heroin, even though there were no opiate substances in the saline. The pleasurable outcome that results from a certain behaviour is called a reinforcing stimulus. The strength of this stimulus in encouraging positive reinforcement via the mesolimbic pathway is directly proportional to how quickly the pleasurable sensation of taking the drug is felt. This is why opiate addicts favour heroin over morphine; the two substances have exactly the same action, but morphine takes considerably longer to exert an influence.
Negative reinforcement describes the process by which a behaviour that turns off or reduces an aversive reinforcing stimulus will come to be favoured. Thus, the painful withdrawal effects that occur when a habitual drug user stops taking a substance often compel them to resume taking the drug to make the withdrawal effects disappear. This acts to reinforcing their drug taking behaviour. It is often said that it is the positive reinforcement that provokes substance abuse to begin with, and the negative reinforcement that maintains a person's drug dependence. However, negative reinforcement can also encourage drug-taking behaviour. An example would be someone with social anxiety who notices one day that they feel better in the company of others after a few alcoholic drinks. From that point, they make sure to always have a few drinks when they are out in public. They may also begin drinking in anticipation of going out, before the stimulus even occurs.
There are many substances and behaviours that human beings find addictive. There are organisations in existence whose aims are to help those who eat too much, gamble too much, drink too much and desire sex too much. There are also recreational drugs that people claim are not addictive, such as cannabis and ecstasy. Studies show however that these substances do cause activation of the mesolimbic dopaminergic neurones, and therefore people do experience positive reinforcement when taking these substances. It pays to remember that, often, people will not know that they're addicted to something until they try to stop doing it. To end, I would like to give all the tobacco smokers out there a fascinating fact. When the decision to stop smoking is made and held to, the withdrawal symptoms experienced that are due to your physical dependence on nicotine last a total of about 24 hours. Any problems that you have with stopping beyond that, therefore, are entirely due to psychological withdrawal.
That mesolimbic system is one powerful bit of wiring.
References
- Bear M F, Connors B W, Paradiso M A, 2001,
Neuroscience: Exploring the Brain , 2nd edition, Lippincott, Williams and Wilkins, Chapters 15, 16 and 18
- Carlson N R, 2004,
Physiology of Behavior , 8th edition, Allyn and Bacon, 573-576
- Davidson G C, Neale J M, 1994,
Abnormal Psychology , 6th edition, New York: Wiley
- Sarafino E P, 1998,
Health Psychology: Biopsychosocial Interactions , 3rd edition, New York: Wiley, 198-199
- Rang H P, Dale M M, Ritter J M, Moore P K, 2003,
Pharmacology , 5th edition, Churchill Livingstone, 595-596
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