Research Summary: The Role of Social Isolation in Addiction Behavior

The pop-science example of the role of social isolation in addiction that most people are familiar with are commonly known as the “Rat Park” experiments.

Throughout the early and mid 20th century, addiction scientists referred to a specific experiment to prove theories about the role of “chemical hooks” in addiction: that certain drugs are just so strong, they automatically create addiction behaviors. This conclusion was drawn from placing a single rat alone in a cage with two options for drinking water: one water bottle filled with pure, distilled water; and one laced with either heroin or cocaine.

Group A: Isolated rats

No matter how many times this experiment is replicated, the rat chooses the drugged water and goes back to continue drinking it until it dies.

The interpretation and extrapolation of this result was simple: that certain drugs are so powerful that living beings will sacrifice everything, even at the risk of its own life, to continue to obtain them.

But in the late 1970’s, psychologist Dr. Bruce K. Alexander of the Simon Fraser University in British Columbia found a flaw in the classic study. He identified that there was a major variable going unaccounted for in these experiments: namely, that rats are highly social creatures and that testing their behavior in isolation is unnatural. In nature, rats typically co-exist in groups of 50-75. So, Dr. Alexander and his colleagues re-ran the experiments providing the same two drinking water options, but using a much larger cage that contained a whole community of rats to reflect natural population sizes. They also filled the cage with nesting materials, toys, food, and other diversions to ensure basic needs were met. He called it “Rat Park.”

Group B: rats in community

In Dr. Alexander’s experiments, published in the journal Psycho-pharmacology, the rats in Rat Park didn’t prefer the opiate-laced water. In fact, they only chose it 25% of the time over the pure water. None of the rats overdosed, nor forgot to eat and died. And most remarkably, when the scientists introduced rats into Rat Park who were already addicted to opiates, the rats voluntarily went through withdrawal and stopped drinking the drugged water.

As it turns out, the problem wasn’t the drugs; it was the cage. It wasn’t natural for the rat to choose getting high, it was unnatural for the rat to be alone.


Humans are significantly more complex creatures than rats. But much like our primate ancestors, we also evolved with a distinct preference and advantage for social bonding. We use complex language forms to communicate with each other, and segregate ourselves into social groups and tribes in order to trade and build multi-layered, interdependent civilizations.

It makes sense, then, that there must be some pretty complex neurochemistry going on behind the scenes to incentivize us to form these social connections. But what’s really fascinating is that the neurochemistry of human social bonding involves opioid compounds, specifically.

The human brain uses naturally-occurring (“endogenous”) opioids to make certain experiences and behaviors literally feel good. The most commonly known ones are called endorphins: the etymology of which is “endogenous” + “morphine.” These compounds have a very similar chemical structure to morphine, heroin, or oxycodone; but they are produced in the brain rather than the lab.

Chemical compound structure

You may have heard that our brains produce these endorphins during physical exercise, which makes it actually feel good to work out. The brain also uses these natural opioids to signal satisfaction when we have a meaningful experience of social connection with another human.

This doesn’t mean transactional social interactions like “hi, how are you, isn’t the weather nice today, that’ll be $17.95.” Our brains use natural opioids to make meaningful social connection feel good: like the last time you had a heart-to-heart conversation with a close friend, partner or lover. Have you ever noticed how you actually feel good after those kinds of conversations, even if they involve subject matter that is dark or intense?

We can see an easy example of how this works with another simple experiment: using naloxone (Narcan) to block the body’s ability to metabolize opioids. Naloxone works to reverse opioid overdoses by blocking the body’s built-in opioid receptors. This means that not only does it protect the receptors from getting overloaded with heroin, but also blocks them from processing any opioids, including naturally-produced ones like endorphins.

If you give naloxone to a healthy person who has not taken any synthetic opioids like heroin, the first thing they report experiencing is a sudden and shocking experience of disassociation and disconnection. They report feelings of loneliness and sadness, even when reading letters from friends and family members who they rationally know to love and care about them.


So, you can imagine what this means for people who don’t have healthy social connections to begin with. This process of natural opioid signaling is missing, and as a result they experience acute neurochemical pain.

Social Connections

Today, we find ourselves living in a world where meaningful social connection is harder and harder to come by. Social media has completely changed the landscape of how we interact with each other, and the jobs that used to offer millions of people de facto social networks are increasingly getting outsourced or automated. When interacting socially, many people are likely to avoid direct contact and interaction by mediating conversation and splitting attention with devices like smart phones. All of this adds up to a picture in which human beings are simply not connecting with each other as often as they used to.

Because of this, a larger and larger segment of the population finds itself lacking the natural opioids that the brain uses to signal satisfaction during connection. As a result, when the US pharmaceutical market suddenly became flooded with readily available synthetic opioids, it was like throwing a lit match into a haystack. The opioid overdose epidemic has been worsening exponentially ever since.


The good news is, it’s possible to re-train the brain in how to produce its own endogenous opioids again after addiction or dependency. Treatment options that promote enhanced states of neuroplasticity through psychoactive medicines like psilocybin and ibogaine can interrupt these patterns and assist with new habit formation. We’re also starting to see some evidence of social programs that help to boost plasticity in the brain and thereby decrease the negative effects of both drug use and loneliness.

In the late 1990s, Iceland implemented a youth social movement that “promoted alternative recreational activities, strengthened family ties, improved self-efficacy, built social competence around comfortably and responsibly relating to others, and broadened cultural experiences.” The results of their program were dramatic: from 1998 to 2016, the percentage of 15-16 year old Icelandic youth drunk in the past 30 days declined from 42% to 5%; daily cigarette smoking dropped from 23% to 3%; and having used cannabis one or more times, fell from 17% to 5%.

Substance use in Iceland amongst 15-16 year old graph

There is another interesting case study from Denmark called Ventilen that pairs people up for connection & friendship. The organization brings 15-to-25 year olds together with volunteers to do a variety of things that may help them build human connections, like playing games, or going to the movies. The results show that 70% of participants felt less lonely after coming, while 74% reported higher self-worth after coming. Sixty-four percent said they were better at social situations, and 80% said they were more likely to meet other people.

Pair of people

In order to reverse the tide of the loneliness and opioid overdose epidemics that are presently ravaging the US population, it is critical that we implement evidence-based programs that address this need for social connection in addiction treatment in parallel to the biological and psychological approaches.