There is no single cause of addiction—rather, genetics, environment, mental health, and various other elements all influence whether someone misuses substances and develops a substance use disorder. These influences are called risk factors and they can work in combination to increase the likelihood of an addiction—however, these influences are not predetermined and are not fate. Just because someone experiences several risk factors for substance abuse, that doesn’t mean they’ll develop an addiction.
Some major risk factors for drug and alcohol addiction include:
- Impulse control traits
- Reward processing
- Drug likeability
- Peer pressure
- Access to substances
- Growing up in a substance-using household
- Parental abuse or neglect
- Co-occurring mental illness
Again, there is no single cause of addiction, but being aware of the risk factors can help you to prevent substance misuse and substance use disorders. And if you struggle with drug and alcohol misuse, treatment can help address your addiction as well as some of these risk factors, such as untreated trauma and mental health disorders.
Biological Risk Factors
There are some key biological elements that play a role in the development of a substance abuse problem. 
Genetics is believed to play a strong (but not decisive) role in determining a person’s likelihood for developing a drug use disorder. Variations in the genes that deal with impulse control, neurotransmitter mechanisms, and reward processing can influence how a person grows up to deal with the risk of drug abuse presented by environmental and physiological factors as well.
Brain chemistry is another area of biology that is directly related to addiction. When a person takes drugs, the chemical compounds in the drugs target the brain’s reward system, which is regulated by the norepinephrine, serotonin, and dopamine neurotransmitters.
Drugs, especially when taken repeatedly over a long period of time, can take over the reward system, forcing the brain to pump out more neurotransmitters and changing the brain’s circuitry to make the drugs the primary source of reward and pleasure.
Genetics is believed to play a strong (but not decisive) role in determining a person’s likelihood for developing a drug use disorder.
Battle in the Brain
The brain’s reward system is the key battleground for addiction. Any pleasurable activity activates the brain’s mesolimbic pathways (the reward network), leading to the release of dopamine, creating an imprint that compels a person to try and seek out the activity again in the future. Drugs are capable of rewriting the pathways, making people obsessed with taking more of the drugs, to the detriment of themselves and everything (and everyone) around them.
This is another biological factor of addiction: the brain’s neuroplasticity, or its ability to adapt to new input, and develop structural and functional changes as a result. Neuroplasticity is how we learn things. It is how the brain grows in response to stimuli. 
Unfortunately, this also happens when the brain is exposed to drugs, which are powerfully pleasant and can force the brain to want more drugs. Hijacking the brain’s neuroplasticity is what makes it so difficult for people addicted to drugs to simply stop taking them. It is the reason why drug abuse can be so persistent, even with treatment.
Tolerance & Withdrawal
Tolerance is a condition where larger doses of drugs are needed in order to achieve even a basic effect, and it is often the result of prolonged drug use. The more drugs a person takes, the more drugs they need to take to recapture the initial sensations they derived from it.
Tolerance is a risk factor for physiological dependence, which means your body has adapted to the presence of the drug and needs it to function normally.
When the drug use is abruptly reduced or discontinued, people often feel powerful and distressing withdrawal symptoms — everything from deep pain and fevers to periods of intense anxiety and depression.
Tolerance, dependence, and withdrawal are biological factors that lock people into a cycle of addiction in order to avoid negative effects. 
Physiological Risk Factors
The body’s physiological systems are those pertaining to its physical and chemical workings. It is a part of the expected functioning of the body, regulating automatic processes that occur inside the body (like sweating when stressed).
Addiction works on the basis of upsetting the regulation and balance between neurotransmitters, the chemical messengers that send signals between the nerve cells in the brain. Psychoactive drugs disrupt how the brain releases and reabsorbs serotonin, norepinephrine, and dopamine. 
Stimulants (like cocaine and methamphetamine), for example, increase the rate of release of dopamine and block the brain from reabsorbing the dopamine, leading to a surplus of the neurotransmitter beyond healthy levels. This is what causes the powerful sensations characteristic of stimulant drugs and what makes the feelings so intense that users immediately seek out more.
Here are some of the key physiological factors behind addiction:
- Rewriting Pathways
The fact that drugs also rewrite the mesolimbic pathways makes for one of the physiological factors of addiction. Continued adaptations to this reward pathway result in natural rewards not having any significant impact. 
The drugs cause such a change that hitherto rewarding activities, like hobbies and recreation, no longer have any effect. Instead, drug-related cues are the only activities that have any response. This creates a strong connection between drug use and pleasure, convincing users that the only way they can feel good is when they take more drugs.
The body’s hypothalamic-pituitary-adrenal axis, or the body’s stress response system, is also affected by chronic drug use. Cortisol, a key stress hormone in the body, can have its production, release, and reuptake disrupted by certain drugs, which is what causes users to feel anxious and vulnerable when they do not have the drugs in their system. This is what precipitates the intense drug cravings that come before a relapse.
- Genetics & Brain Functions
Chronic drug use can cause structural and functional disruptions to the brain, specifically in the hippocampus, the prefrontal cortex, and the amygdala, all of which combine to regulate memory, emotional regulation, decision-making, and impulse control. 
Changes in these regions of the brain can weaken the resolve to stay sober, make drug-related cues look more appealing, and get in the way of rational thought. This is why recovery can be so difficult for people who have experienced drug addiction.
Genetics and physiology overlap when it comes to addiction. Certain genetic variations can change how neurotransmitters, receptors, and enzymes work, effectively tampering with the entire reward-processing network of the brain. While physiology alone will not make someone start taking drugs, a person with these genetic predispositions is more at risk of developing a drug problem if their environment also reinforces the predispositions.
Environmental Risk Factors
A person’s environment — the people they spend their time with, where they live, what kind of household they grew up in, and other factors — can play a significant role in the likelihood of whether they might develop a substance abuse problem.
Peer influence is a significant environmental factor in the development of a substance use disorder, especially peer influence during adolescence, when young adults are going through many changes and looking to find their identity and fit in with their desired social groups. 
Social expectations among certain groups can encourage risky behavior, such as unsafe sexual practices, and drug use. Being among peers who participate in drug misuse increases the likelihood of a person (especially an adolescent) trying drugs and, if other biological and physiological conditions are met, likely developing an addiction.
The family environment is also an important catalyst in the development of a drug problem. Even if family members themselves do not abuse drugs, growing up with dysfunctional behaviors like abuse, neglect, and inconsistent parenting can make a child more vulnerable to addiction.
Of course, growing up in the presence of family members who also use substances is a significant predictor for future drug use too. Seeing a parent or an older sibling abuse substances normalizes the consumption of drugs and creates a family environment that can breed substance abuse.
Socioeconomic Factors & Availability of Drugs
Socioeconomic factors include poverty, unemployment, geographic location, and lack of educational or professional opportunities. All of these, either individually or in combination, can contribute to the likelihood of a person being at risk for a drug problem.
Socioeconomic factors can determine stress, limited access to education or healthcare, and a sense of despair and hopelessness at life prospects. Many people experiencing stress as a result of their socioeconomic situation turn to drugs as a method of self-medicating and coping with their problems. 
Environmental factors for drug abuse also include the degree of availability and accessibility to drugs. Whether through clandestine drug markets or legal prescription medication, being able to purchase or obtain drugs with minimal effort or risk is a considerable predictor for developing an addiction, especially if other risk factors are present. Regardless of the type of substance, communities that have a high availability of drugs are often the ones with the highest rates of substance abuse.
Trauma & Addiction
Traumatic experiences and posttraumatic stress disorder (PTSD) can increase the risk of addiction.  People who have been exposed to and who have experienced abuse (physical, sexual, emotional, or psychological), naturally struggle with the mental toll of what they went through. Without guidance and help, they often turn to harmful coping mechanisms, usually self-medicating with drugs or alcohol to escape their adverse experiences.
Not all trauma has to be violent. Significant stressful life events, like losing a loved one, getting laid off, the end of a relationship, or financial woes, can also compel people to seek comfort in unhealthy behaviors, including substance abuse and addiction. This may be especially true if someone experiencing one or more life stressors has easy access to drugs or has some other factor that makes it likely that they might develop a problem.
Traumatic experiences, such as exposure to abuse, neglect, death of a loved one, natural disasters, combat, and life-threatening experiences can increaes the risk of addiction.
Mental Health & Addiction
There is a close connection between mental health and drug addiction. People who struggle with addiction are more likely to also have a mental health condition, and vice versa.
The National Survey on Drug Use and Health notes that among adults with a substance use disorder, 45.1% had a co-occurring mental health condition. For adults who have a mental illness, 18.2% had a co-occurring substance use disorder. 
Some mental health disorders are particularly associated with an increased risk of addiction. People who have had major depressive episodes within a prior year are more likely to also have had a substance use disorder compared to people who haven’t had any periods of depression, according to the Substance Abuse and Mental Health Services Administration.
- Anxiety & Bipolar Disorder
The same holds true for anxiety disorders. People who experience various forms of anxiety tend to have higher rates of substance abuse disorders. People who have post-traumatic stress disorder, for example, have a higher risk of developing an addiction because of the risk of using drugs or alcohol to self-medicate. 
People who have bipolar disorder have significantly higher rates of substance abuse compared to people in the general population who do not have bipolar disorder. People with bipolar may be compelled to take stimulants during their manic phases, for example, and they may take opioids during their depressive periods. 
Different substances of abuse are associated with specific mental health disorders.
Alcohol use disorder tends to happen with depression. People with depression find that alcohol alleviates their symptoms, so they self-medicate by drinking.
Stimulants, like methamphetamine and cocaine, have been known to cause increased anxiety, while opioid use disorder is associated with depression and other mood disorders. 
- PTSD & Substance Abuse
The close association between trauma and substance abuse means that people who have post-traumatic stress disorder (PTSD) are more likely to abuse substances. 
People who have witnessed or experienced trauma may use drugs or alcohol as a way of coping with the powerful emotions, disruptive thoughts, and other ways that their quality of life has been affected by the trauma. Certain drugs, or periods of unhealthy alcohol consumption, can temporarily alleviate or numb the anxiety, depression, or other expressions of emotional pain that stem from the traumatic experience.
Emotional regulation is another area where PTSD and substance abuse intersect. Witnessing or experiencing a traumatic incident can disrupt a person’s ability to regulate their emotions, either by making them very emotional to neutral stimuli or making it difficult for them to appropriately show emotions. By using drugs or alcohol to numb their emotions or to make them more likely to be emotional, substance abuse provides an illusionary sense of control or emotional relief while leaving the PTSD itself unaddressed. 
Guilt & Substance Abuse for Bonding
Trauma can often lead to feelings of guilt, shame, and self-blame, even (sometimes especially) if the person who witnessed or experienced the trauma was innocent of any wrongdoing. While drugs or alcohol can be abused to numb these emotions, some people engage in self-destructive behaviors (of which substance abuse is an expression) as a form of self-sabotage, believing they are punishing themselves for their perceived guilt. 
Some people who have witnessed or experienced trauma can use drugs or alcohol to bond with others who have shared similar experiences because of the way that trauma fosters feelings of isolation, mistrust, and detachment, making it difficult to form and maintain healthy social relationships. Other people may eschew connecting with other survivors entirely and instead drink or use drugs because they feel lonely.
Raising Awareness to Prevent Addiction
There are many ways to prevent addiction. Some of the most effective methods include the following:
- Education: Teaching people about the risks of substance and alcohol abuse can go a long way toward prevention. This can happen through school and community programs, advertising, and any kind of outreach.
- Early intervention: This is a key part of preventing addiction. If someone is showing signs of drug use, such as sudden changes in behavior or reduced quality of life, connecting with them, getting them into treatment, and supporting their recovery can save them from getting caught in the spiral of addiction.
- Healthy behaviors: Promoting a healthy lifestyle is a vital part of raising awareness about addiction while also preventing it from taking hold. A healthy diet, regular exercise, and consistent sleep all play a role in reducing the risk of addiction, even (and especially) for people who have that genetic component for addiction.
- Coping skills: Similarly, healthy coping skills, like having a strong social network, and practicing good mental health, can prevent addiction during stressful and difficult periods of life.
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