Addictions are a group of complex illnesses in which both genetic as well as environmental causes play their part. These diseases have a chronic and relapsing course with remissions lasting from days to years. Addictions typically appear as the uncontrolled and repetitive use of a drug or an activity, with outcomes harmful to the individual and those around him.

Addictions demand exclusive rights to a person’s time, effort and mind space and because of this overdemanding nature of the phenomena, addictions destroy work, family life, and social relationships. Although consumption of addictive agents and involvement in addictive behaviours are voluntary, they sooner or later lead to volitional control being compromised because of the compulsive nature of addictions.

This chapter takes up a frequently asked question: to what extent are the processes involved in the initiation and maintenance of addiction influenced by genetics and to what extent by the environment?

In general, there are three types of genetic evidence which can tell us whether an illness is hereditary or not. These are:

1. Family Studies: If the occurrence of an illness is higher in the first-degree relatives (parents, siblings, children) of a person suffering from an illness as compared to the second-degree relatives (cousins, uncles, aunts, nephews, nieces), who in turn have higher rates as compared to the general population, it is strongly indicative that heredity has a role to play. However, close family members also share the same environment and so family studies alone may not be enough to prove that heredity is responsible for addictions any more than shared environment.

For example, if the parents drink, chances are high that bottles of whiskey or vodka may be lying around the house and be easily available to an adolescent. Chances are also high for the parents to be more tolerant of their child taking a sip once in a while than in a family where everybody is a teetotaller. So, how do we know if the reason is the parents’ genes or their permissive attitude?

2. Adoption Studies: If children who are adopted soon after birth show a higher incidence of addictions when they grow up than the members of their adopted family and that incidence is more like the incidence in their biological family, it would mean that genetics plays a more important role in causing addictions than the environment. If the opposite is true, one would be correct in concluding that environmental factors are more important in causing addictions than genetic factors.

3. Twin Studies: Identical twins share genetic material which is the exact replica of each other, while non-identical twins, genetically speaking, are like regular siblings. When both members of a pair of twins suffer from the same illness, they are said to be concordant for that illness. If concordance rates for an illness in a series of identical twins are much higher than concordance rates in a series of non-identical twins, it is safe to assume that in the causation of that particular disease, genetic factors have a major role to play since the environment during early childhood is the same for both sets of twins.

In the case of addictions, family, adoption, and twin studies all show that an individual’s risk for addiction tends to be proportional to the degree of genetic relationship to a relative with addiction. Various genetic studies have shown that addictions have a moderate to high hereditability. A safe estimate would be that at least 50% of the burden of causation is shared by genetic factors and the rest by social and environmental factors such as the availability of drugs and stress.

A significant view on the shifting balance of genetic and environmental influences has been obtained from the developmental perspective. The Virginia Twin Study, in a series of publications, revealed that in early adolescence the initiation and use of nicotine, alcohol, and cannabis are more strongly determined by familial and social factors like permissiveness and availability, but these gradually decline in importance during progression to young and middle adulthood, when the effects of genetic factors become the maximum.

As a broad rule, environmental and social factors like easy availability and social sanction are more important in initiating drug use at a young age and genetic factors play a more important part in determining who eventually becomes addicted and who does not. Simply put, if a drug is available during adolescence and parental controls lax, there are more chances of a young person using that drug but not all of them grow up to be addicted to those drugs. To a large extent, genetic factors determine who does and who does not.

The moderate to high heritability of addiction disorder is paradoxical because addictions initially depend on the availability of the addictive agent, and it is the individual’s choice to use it or not. The availability of addictive agents is determined by the culture, social policy, religion, economic status and narco-trafficking, and it changes across time and place. Thus, the Twin Studies on addiction indicate that under particular societal scenarios, genes play a substantial role in causation of addictions. Like other complex diseases such as obesity, diabetes, cancer and coronary heart disease, addictions are strongly influenced by genetic background but also by lifestyle and individual choices.

However, what is inherited is a generic addiction trait, not the propensity to develop addiction to a specific drug or behaviour. In a genetically predisposed person, which drug or behaviour the person will get addicted to would depend totally upon access, permissiveness and the environment.

One summer, a couple of years back, a young man was brought by his parents and twin brother to my outpatients’ clinic for treatment. It was a nuclear family unit, which was a part of an extended business family living in connected houses and involved in wool trade in the downtown part of the city. The patient was in his late twenties and had been using heroin for several years. He had been admitted multiple times to psychiatry and addiction treatment units at various city hospitals. Each of
these admissions had resulted in remissions lasting a few weeks to a couple of months. Repeated questions by the resident psychiatrist about history of addictions in any other members of the family was met with indignant denials.

This of course is possible, but here we had the patient’s identical twin sitting right next to him, whom the family swore was totally unlike his brother – highly responsible, an ideal son and utterly devoid of any addiction.

I sensed that the young man (the ideal twin) had something in his mouth. As things unravelled, it came to light that he had been using tobacco for even longer than his twin brother had been snorting heroin. And a dentist’s warning one year back after he discovered a suspicious patch of discoloured mucosa in his mouth had made no difference. Also, the father had been drinking half a bottle of whiskey every day for over 15 years even after a diagnosis of inflammation of the oesophagus. None of them were considered by the family to be addicts since alcohol and tobacco were not thought to be addictions.

Also, the patient’s uncle, the father’s brother, had left home at the age of 25 without telling anybody and was gone without a trace. After 15 years, a neighbour had spotted him in an ashram adjoining a temple in Haridwar with a group of ganja-smoking sadhus, whom he was living with. This indicated a mixed behaviour and drug addiction. When the family went to see him, he had met them cordially but refused to go back home saying that he was happy where he was. However, none of these three members of the family were considered to be suffering from an “addiction” like the young man with heroin use. They were not even considered fit to be mentioned in the context of addictions even after being specifically asked about addiction in any other family member.

As for me, looking at the family afresh provided me with the possible genetic connection between the patient’s heroin addiction, his twin brother’s advanced nicotine addiction, his father’s alcoholism and his uncle’s behavioural and cannabis addiction.

Excerpted with permission from Most of What You Know About Addiction is Wrong, Anirudh Kala, Speaking Tiger Books.