The science behind heroin: How it hijacks the brain

In her book Dopamine Nation, psychiatrist and author Anna Lembke describes how addiction alters the balance of pleasure and pain in our brains. This process is not unique to heroin and can happen from any pleasure-inducing behaviour that’s taken too far.

Research suggests that both painful and pleasurable sensations have ‘extensive similarities in their anatomical substrates’ – meaning it’s suspected that they originate in the same areas of the brain. The opioid and dopamine systems both have important roles in modulating these sensations.

Existing in the same areas of the brain suggests that these sensations are highly related – and what affects one affects the other. The brain tends to move towards homeostasis: it tries to find a balance. Repeatedly engaging in a pleasurable activity changes this balance over time. The more pleasure is activated, the more the brain, looking to find a balance, moves the threshold, balancing pleasure and pain. What this eventually looks like is a brain tipped towards pain at baseline that requires higher levels of pleasure-inducing chemicals to feel normal.

This process that Lembke describes is just one way that heroin hijacks the brain.

What is heroin?

Heroin is also known as diamorphine, which is prescribed to treat moderate to severe pain. It is very cautiously prescribed due to its negative health effects like acute respiratory depression, and its risk of creating dependence. This means it is usually only prescribed in severe circumstances, such as palliative care or pain relief for cancer treatment.

Heroin has been around since the 1870s, and its addictive properties came to light very quickly. It works by converting to morphine in the body and binding to your opioid receptors, which causes pleasurable feelings, a sensation of heaviness but also itching, nausea and sometimes vomiting.

The neurobiology of heroin

Heroin addiction involves complex neurobiological processes that affect several brain regions and neurotransmitters. It targets the brain’s mu-opioid receptors but also affects many other brain regions – the basal ganglia, amygdala and prefrontal cortex, and multiple neurotransmitters – dopamine, corticotropin-releasing factor, norepinephrine and glutamate.

The body has endogenous opioids circulating in the nervous system. These regulate pain and pleasure, as well as respiration. Heroin is an exogenous opioid that targets your opioid receptors. It blocks pain signalling, which is why diamorphine is still used as a painkiller.

Heroin indirectly affects the dopamine reward system by suppressing activity that, in turn, normally suppresses dopamine release. This inadvertent effect on the dopamine system causes heroin to be rewarding. This is an important factor in understanding what makes heroin so addictive – but it isn’t the only one.

The cycle of addiction to heroin begins with the stimulation of rewarding pathways in the brain, especially in the basal ganglia, through the opioid and dopamine systems. This process is powerfully reinforcing and will make the user want to repeat the process. During withdrawal, the amygdala is involved in the stress responses that make the user feel acutely unpleasant, further reinforcing the cycle—disruptions in the prefrontal cortex cause strong cravings and drug-seeking behaviour. One of the signs of heroin addiction is re-administering heroin to stave off unpleasant withdrawal symptoms.

How heroin affects decision-making

The prefrontal cortex is one of the last areas of the brain to mature and is involved in a lot of higher-order processing. We process moment-to-moment input there and compare it to past experiences. It is responsible for a lot of our ability to plan and for our ability to use foresight. Damage to this area causes disinhibition, apathy, loss of initiative and personality changes.

Chronic drug use leads to ‘hypofrontality’, which causes the prefrontal cortex to become less effective. This isn’t unique to heroin and happens with all drugs of abuse. This happens both through the imbalance of neurotransmitters like dopamine and glutamate and altered neuronal connectivity.

With the prefrontal cortex not performing as it should, the user finds it much harder to resist drugs and drug-related cues. Additionally, emotions are impaired, leaving the user more vulnerable to stress and negative emotions, which they then try to eradicate with more heroin.

Long-term effects on the brain

Heroin abuse causes long-term changes in the brain. It’s associated with reductions in both grey and white matter, which affects emotions, behaviour, motor control and reactions to stress. Both dopamine and the brain’s natural endorphins, which heroin mimics, are downregulated. This means the receptors for these neurotransmitters become less sensitive as the brain is trying to compensate for high levels of heroin in the brain (remember the brain’s tendency to move towards homeostasis). This is a key component of post-acute withdrawal syndrome and is one of the reasons that people who abstain from heroin or any other drug may find it hard to experience pleasure for a while after quitting. This is a major driver of relapse.

Structural and neurochemical changes in the brain lead to impairments in executive function, memory and mood. The risk of mental health disorders is elevated.

Challenges of overcoming heroin addiction

Coping with both these brain changes and abstinence from heroin is difficult.

Recovery involves sustained effort, determination, support, and a realistic outlook. The changes in the brain are difficult to cope with and increase the desire to relapse. Getting professional support to kick heroin is the best approach and will give you tools to sustain your sobriety.

Managing withdrawals using medication like methadone and buprenorphine play a key role in managing withdrawal symptoms. After this, the more support can be put in place to manage your long-term recovery plans, the better. These should come from several angles – medical, social, behavioural and psychological.

Medical interventions will involve medication-based treatments to assist with abstinence. These can be opioid receptor antagonists like naltrexone and antidepressants to combat the anhedonia and mood dysregulation that can remain after heroin is discontinued.

Behavioural therapies like CBT and Contingency Management are used to help the person in recovery change their behaviours and beliefs around heroin. Contingency Management involves offering external incentives for abstinence, while CBT helps to identify thoughts, beliefs and behaviours that are unhelpful so they can be challenged and managed.

Individual therapy comes in many forms, such as Dialectical Behavioural Therapy and trauma therapy. They can help you talk about the underlying causes of your addiction and give you different ways of processing and coping with them.

Social interventions can be as simple as reaching out to friends and loved ones for support, but more structured interventions like family therapy, group therapy and 12-step programmes help combat isolation and increase accountability.