What causes addiction, and why is it so hard to treat?

As of 2021, more than 36 million

people worldwide were estimated to be experiencing

substance abuse disorder. This condition spans a spectrum

of patterned drug use that causes issues in a person’s life. At the more severe end of the spectrum

is substance addiction. To understand why some people are

more susceptible to addiction and why it can be so difficult to treat, let’s take a look at how addictive drugs

affect the body. When someone repeatedly uses

an addictive substance, their brain may adjust to account

for its regular presence. This is called tolerance;

it diminishes the drug’s effect and means more is required

to produce the same experience. Alcohol, for instance, increases the

transmission of chemical messengers like endorphin and GABA, which promote sensations

of pleasure and calmness. When someone uses alcohol frequently,

their brain will adapt to its presence. So when they don’t use it,

their brain receives fewer signals from those pleasure- and

calm-inducing neurotransmitters, which impacts their energy and mood. In addition to the unique effects

each addictive substance has, all of them alter the release of dopamine in a brain region called

the nucleus accumbens. This area is part of the brain’s

reward pathway, which is sensitive to experiences

that give us pleasure and drives us to repeatedly seek them out. The reward pathway is essential

to our well-being— but addictive substances also exploit it. When someone is repeatedly

using a substance and their body has adapted

to its presence, they may develop dependence where the drug is necessary

for them to function comfortably. Meanwhile, repeated use can decrease

the influence of the brain’s cortex, which is responsible for driving

deliberate decision-making and limiting impulsive behaviors. And it can increase the influence

of the brain’s subcortex, which is crucial in habit-learning

and impulsivity. Together, these changes can make

someone feel a lack of control over how they’re using a substance. This can mean suffering

in other facets of their life and taking risks to continue using it. If the substance leaves their system,

their body's equilibrium is disrupted, so they may experience cravings

that motivate thoughts and behaviors of seeking and using the drug. And if they continue without

the substance, they may experience withdrawal. Opioids, for example,

relieve pain and induce sedation. Withdrawal from them causes

heightened pain, anxiety, and insomnia. The faster a drug reaches the brain

and stimulates the reward pathway, the more addictive it is. For example,

heroin and morphine have similar effects, but heroin’s chemical structure

enhances its ability to penetrate the blood-brain barrier

and bind to specific receptors. This makes it faster acting

and more addictive than morphine. Meanwhile, compared to nicotine patches

and gum, regular and electronic cigarettes

are more addictive because smoking and vaping

deliver nicotine to the brain fastest. Depending on their chemical structure

and mode of delivery, drugs vary in how addictive they are— but people also vary in how susceptible

they are to substance use disorder. Scientists think this is due to a mix

of life experiences and genetically inherited traits, though neither predetermines addiction. Trauma and mental health conditions appear

to make people more susceptible. And, overall, using addictive substances

before 18 is considered a strong risk factor. This is in part because the reward

pathways of younger brains are especially sensitive. Many of the genetic factors at play

remain unknown, but some genes do seem to track

with certain substance use disorders. For example, specific genes increase

the risk for nicotine addiction by making certain receptors

more sensitive to nicotine and withdrawal from it more difficult. At the same time, some genes actually make people

more resistant to substance use disorders, such as genes that slow

the breakdown of alcohol, leading to unpleasant side effects that

make people less interested in drinking. In fact, one drug that treats

alcohol use disorder operates with this very mechanism. Detoxing from a substance the body

has become dependent on can be extremely difficult. And in some cases, abruptly quitting

can also be physically risky, so it isn’t always advised. Beyond detoxing, quitting is

often a long-term process. It’s aided by treatment plans

that prioritize addressing underlying conditions; developing new associations

with experiences previously linked with drug use; and creating safe,

supportive environments. Ultimately, both addiction and recovery

are the results of a brain with an incredible ability to adapt

from experience.