February 28, 2011
Addiction is a major health problem that costs as much as all other mental illnesses combined (about £40 billion per year) and about as much as cancer and cardiovascular disorders also.
At its core addiction is a state of altered brain function that leads to fundamental changes in behavior that are manifest by repeated use of alcohol or other drugs or engaging in activities such as gambling. These are usually resisted, albeit unsuccessfully, by the addict. The key features of addiction is therefore a state of habitual behaviour such as drug taking or gambling that is initially enjoyable but which eventually becomes self-sustaining or habitual. The urge to engage in the behaviour becomes so powerful that it interferes with normal life often to the point of overtaking work, personal relationships and family activities. At this point the person can be said to be addicted: the addict’s every thought and action is directed to their addiction and everything else suffers.
If the addictive behaviour is not possible e.g. because they don’t have enough money then feelings of intense distress emerge. These can lead to dangerously impulsive and sometimes aggressive actions. In the case of drug/alcohol addiction the situation is compounded by the occurrence of withdrawal reactions which cause further distress and motivate desperate attempts to find more of the addictive agent. This urge to get the drug may be so overpowering that addicts will commit seemingly random crimes to get the resources to buy more drug. It has been estimated that about 70% of all acquisitive crime is associated with drug and alcohol use.
Addiction is driven by a complex set of internal and external factors. The external factors are well understood: the more access to the desired drug or behaviour e.g. gambling the more addiction there is.
The internal factors are less clear. Although most addiction is to alcohol and other drugs, addiction to gambling and other behaviours such as sex or shopping can occur. These tell us that the brain can develop hard-to-control urges independent of changing its chemistry with drugs. All addictions share a common thread in that they are initially pleasurable activities, often extremely enjoyable. This results in these behaviours hijacking the brain’s normal pleasure systems so that naturally enjoyable activities such as family life, work, exercise become devalued and the more excessive addiction behaviours take over.
However, not everyone who engages in drug use or gambling becomes addicted to them so clearly other factors are important. These are not yet understood but are now being actively studied. Some people may be particularly sensitive to the pleasurable effects of alcohol, drugs or gambling, perhaps because of coming from deprived backgrounds. In others, addiction may occur because of an inability to adopt coping strategies. Others may have an underlying predisposition to develop compulsive behaviour patterns. Some unfortunate people may have several of these vulnerability factors and there are also genetic predispositions to some of them.
Also a significant amount of drug use is for self-medication, examples include cannabis for insomnia, alcohol to reduce anxiety, opioids for pain control etc. This therapeutic use can escalate into addiction in some people though by no means all. Not all drugs which are used for recreational purposes are addictive. LSD and magic mushrooms seem not addictive at all, and some have a low risk of addiction (MDMA/ecstasy; cannabis). The most addictive drugs are nicotine, heroin and crack cocaine plus metamfetamine (crystal meth) although this is not much used in the UK.
Just because some people – including leading politicians – have used drugs but stopped before they became addicted does not mean that anyone can stop that easily. Starting to use drugs may be a lifestyle choice but once addiction sets in, choosing to stop is very much more difficult if not impossible.
We are beginning to understand how addictions start in the brain. The pleasurable or rewarding effects of addictions are mediated in the brain through the release of chemicals such as dopamine [by cocaine, amphetamines, nicotine] or endorphins [heroin] or both [alcohol]. The pleasures are then laid down as deep-seated memories, probably through changes in other neurotransmitters such as glutamate and GABA that make memories. These memories link the location, persons and experiences of the addiction with the emotional effects. These memories are often the most powerfully positive ones the person may ever experience, which explains why addicts put so much effort into getting them again. When the memories re-occur, which is common when people are still using drugs or gambling, as well as when in recovery/abstinence, they are experienced as cravings. These can be so strong and urgent that they lead to relapse.
A great deal of research has been conducted into the role of dopamine in addiction and we now know that the number of dopamine receptors seems to predispose to excessive pleasure responses from stimulant use. This excessive response is thought to initially occur in the reward centre of the brain – [the nucleus accumbens] – but then move into other areas where habits are laid down. This shift from voluntary (choice use) to involuntary (habit-use) explains a common complaint of addicts that they don’t want to continue with their addictions, and even that they don’t enjoy them anymore, but cant stop themselves. In this sense addiction can be seen as a loss-of-control over what starts out as a voluntary behavior. Thus addiction is not, as some like to suggest, simply a “lifestyle” choice. It is a serious, often lethal, disease caused by an enduring (probably permanent) change in brain function.
We know that personality traits especially impulsivity, predict excess stimulant use and in animals this can be shown to correlate with low dopamine and high opioid receptor levels. Similarly in humans low dopamine and high opioid receptor levels in brain predict drug use and craving. These observations give new approaches to treatment, both psychological interventions such as behavioural control, and anti-impulse drugs such as those used for ADHD e.g. atomoxetine and modafinil, are being tested.
For some addictions, especially heroin, the risk to the addict (life expectancy less than that from many cancers) and to society (from crime and infections), is so high that the prescription of substitute opioid drugs or even heroin itself saves lives and reduces crime. These substitute drugs are methadone and buprenorphine [Subutex]. As well as reducing crime and social costs by removing the need for addicts to commit offences to feed their habit, they also protect from accidental overdose and reduce risk of infections such as HIV and hepatitis. Similar substitute pharmacological approaches exist for other addictions e.g. gammahydroxybutyrate (Alcover) and baclofen for alcohol addiction, and varenicline (Champix) for nicotine dependence.
Another major reason for relapse in addiction is stress. This may work through increasing dopamine release in brain so priming this addiction pathway or by interactions with other neurotransmitters such as the peptide substance P. As antagonists of these neurotransmitters are now available they are being tested in human addictions and may offer an alternative to substitution treatments.
Nutt DJ King LA Phillips LD (2010) Drug harms in the UK: a multicriteria decision analysis Lancet 376: 1558-66
Nutt DJ Lingford-Hughes A (2008) Addiction the clinical interface Brit J Pharmacology 1-9
Nutt DJ, Law FD (2008) Pharmacological and Psychological aspects of drug abuse. New Oxford Textbook of Psychiatry 2nd edition
Robbins TR, Everitt B, Nutt DJ (2010) The Neurobiology of Addiction – New Vistas. OUP