The Neurological Effect of Illegal Substances and Alcohol on the Brain

This article explores the neurological effect of substance and alcohol abuse and explores the treatment options available from the British healthcare system, the NHS.

By Ipshita Rishi

Published 1:07 PM EST, Tues Aug 10, 2021


The brain is unarguably the most complex organ in the human body, as it is still an organ yet to be fully understood. The brains’s complex structure & composition continues to be the topic of academic research & composition. 

Surrounding the world of alcohol and drugs lies a huge psychological illness, addiction. Seen as a taboo in many societies, addiction causes more than 750,000 deaths globally each year. Addiction is an individual’s compulsive behavior towards a substance or activity that includes pleasure and enjoyment, later suffering from withdrawal and tolerance issues, it is classed as a medical disorder – rather than a habit – and requires treatment just like other diseases and illnesses. The most common type of addictions include: drugs, gambling, alcohol, smoking, sex and food. According to the charity Action on Addiction, 1 in 3 people struggle with addiction. 

But what has addiction got to do with the brain? When someone develops an addiction, the brain craves the reward of the substance or activity. This is due to the intense stimulation of the brain’s reward system, known as the mesolimbic dopamine pathway. It is located in the cerebrum in the brain and is a set of structures that deals with emotions, memory and basic instincts. The brain is responsible for regulating temperature, emotions, decision-making, breathing and coordination. This major organ also impacts physical sensations in the body, emotions, cravings, compulsions and habits. Under the influence of powerful substances such drugs and alcohol can cause alterations in the brain. The substances react with the mesolimbic system in order to release strong feel-good emotions which affect the body and mind. Our brains reward us when we do something that brings pleasure, to illustrate for a drug addict the pleasure would be substance use thus creating a cycle of drug use and intense highs. This eventually leads to them taking drugs for the release of hormones that make us feel happy, such as dopamine, oxytocin, serotonin and endorphins (these are known as D.O.S.E chemicals).

It is important to classify the different types of drugs and understand them on a molecular level in order to understand its neurological effects. In order to classify drugs, we must first  understand what drugs are. The dictionary definition of drugs are: “a medicine or other substance which has physiological and psychological effects when ingested or introduced to the body.” Although not commonly seen as one, alcohol is also classified as a drug, except it is not an illegal substance under UK laws. However, commonly known substances Such as as heroin, opium and cannabis are illegal substances. Illegal substances refer to drugs forbidden for consumption, possession and exchange by the law. There are 8 main categories that drugs can be classified into: depressants, stimulants, hallucinogens, dissociative anaesthetics, narcotic analgesics, inhalants, agonists, antagonists and reuptake inhibitors. It is important to also remember that a single drug can overlap, meaning that a drug could be a stimulant, hallucinogen, inhalant and agonist!

So how does the NHS manage people with addiction? The first steps to tackling and seeking help for addiction usually starts either with your GP or local addiction treatment services. In most circumstances the patient will be assigned to a key worker who helps work with the patient to plan the right treatment. Treatments include: therapy (such as CBT), medication, detoxification and self-help. Rehabilitation is not an easy process on the NHS, and it is only granted in severe and critical cases of addiction. Funding is difficult to obtain and the process involves applying to the government for a lump sum of an individual patient’s treatment. With funding and budgets getting tighter, only chronic and the most deserving cases are encouraged to apply. So should the NHS increase the funding for addiction patients?

Drug Misuse and the Neurological Effects

So what do the different classifications mean? Depressants slow down the CNS and decrease the speed of synapses to transmit responses. Examples of depressants include alcohol, opioids and heroin. Stimulants are the opposite of depressants, they stimulate the CNS and increase the speed of synapses to transmit responses, examples are: caffeine, nicotine and ecstasy. Hallucinogens alter the perception of reality and change sense of smell, taste and sight, examples are: ketamine, magic mushrooms and LSD. Dissociative anesthetics include drugs that inhibit pain by cutting off or dissociating the brain’s perception of the pain. PCP, its analogs, and dextromethorphan are examples of dissociative anesthetics. Narcotic analgesics relieve pain, induce euphoria, and create mood changes in the user. Examples of narcotic analgesics include codeine, morphine and oxycontin. Inhalants include a wide variety of breathable substances that produce mind-altering results and effects. Examples of inhalants include Toluene, paint, gasoline, hair sprays, and various anesthetic gases. Agonists causes a brain chemical that stimulates the receptor associated with a particular neurotransmitter, elevating its effects. Antagonists are molecules which do the opposite of agonists, they inhibit the action of receptors associated with a neurotransmitter. Reputable inhibitors are chemicals which stop a neurotransmitter being reabsorbed by sending neurons, thus causing antagonistic responses. To put it in context, let’s take the example of dopamine antagonists. Dopamine antagonists block the action of dopamine. They have profound importance in several antipsychotic diseases such as schizophrenia, bipolar disorder, and psychosis. They are also used in non-psychotic illnesses such as orthostatic hypotension, vomiting, and nausea.

Common, well-known “street drugs” contain heavy amounts of carbon, hydrogen and nitrogen, they are referred to as alkaloids. Alkaloids are any class of nitrogenous organic compounds of plant origin which have pronounced physiological actions on humans, such as drugs and poison. 

The brain is made up of more than 100 billion nerves that communicate in trillions of connections called synapses. The brain’s reward system evolved because it helped us seek out things that are important for our survival, but if this system is hacked, it leads to addiction. The reward pathway can be divided into 6 steps: stimulus, urge, desire, action, reward and learning. These are how the 6 steps work:

Stimulus: the initial stimulus can originate outside the body, such as the sight of drugs, or from within, such as falling dopamine levels. 

Urge: dopamine released from the VTA to the nucleus accumbens drives us to seek out and work for the reward that is linked to the stimulus. 

Desire: the urge may be registered as a conscious desire in the cortex, but sometimes it goes undetected, or even opposes our conscious desires. 

Action: a region of the frontal cortex weighs the inputs and decides whether to seek the reward, the body then acts to reach it. 

Reward: the reward triggers parts of the brain known as “hedonic hotspots” to release opioid-like neurotransmitters, giving a sense of pleasure. 

Learning: if the reward is better than expected, the brain relaxes more dopamine, strengthening the connection between the stimulus and reward.

Research and experiments have shown that substance and alcohol abuse can cause severe symptoms both neurologically and physiologically. Common physical symptoms include  changes in appetite appearance changes sleeplessness, injury or disease caused by substance abuse and increased tolerance to the source of addiction. Excessive and prolonged usage has also shown disruption of nutrients reaching the brain needed by brain tissue, direct damage and apoptosis of brain cells, including neurotransmitter receptors,  alterations to brain chemicals and concentrations and deprivation of oxygen to brain tissues.


A study done in 2013 showed that alcohol shrinks the hippocampus and the use of methamphetamine shrinks the amount of great matter in the brain’s frontal cortex, among other areas leading to a decline in mental function. Such long term effects can cause permanent brain alterations and future health problems such as slurred speech, physical imbalance caused by an inefficiency cerebellum cortex, brain atrophy, memory loss, cognitive decline and as discussed before, addiction. Although the effect of substance abuse on people is different, it can still lead to a very bad lifestyle and harmful effects. Your body will react differently to substances based on the type of drugs, strength of drugs, how it is being taken, what is present in your bloodstream during absorption, existing health condition and how many different types of drugs are taken at once. 

Although a treatable illness, addiction took hold of the UK and cost the NHS millions of pounds. In 2016, the National Treatment Agency (NTA) estimated the cost of the NHS of treating drug misuse at around £500m a year and alcohol misuse as much as £3.5bn a year. Substance abuse and alcohol abuse are seriously harmful, and it is vital that the government increase the funding for education and awareness of sensitive topics such as addiction. If you know anyone who needs help with substance abuse or addiction, please contact a health care worker as soon as possible. 

Ipshita Rishi, Youth Medical Journal 2021


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Ipshita Rishi, Youth Medical Journal 2021


By Ipshita Rishi

Hi! I am an aspiring medical student from the UK, with a passion for writing and academic research. I throughly enjoy talking and debating, especially topics relating to science and medicine. My particular areas of interest are: neuroscience, immunology, oncology, psychiatry and You can also see more of me on my website:

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