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How Do Drugs Work in the Body?

Gaining a deeper understanding of drugs and addiction means diving into how chemicals can affect the body. Drugs can be used to save lives, improve your quality of life, and seek pleasure.

But they often have consequences.

The body is complicated, especially the brain. There is always more to understand about the body, and the way drugs and chemicals can help or hurt them. For now, it’s important to know the risks of both prescribed and illicit drug use.

The Chemical Message Highway

It’s important to understand the brain’s messaging system, to learn the way psychoactive drugs work. Your nervous system runs throughout your entire body, and it’s controlled by your brain. Everything from your conscious thoughts to your blood pressure is controlled through this system. Psychoactive drugs are chemicals that change your brain function by altering perception, consciousness, mood, cognition, and behavior. They do this by affecting your messaging system.

Your brain and body communicate through a system of nerve cells, which are called neurons. These neurons pass messages using chemicals called neurotransmitters. When two neurons come together, they pass the neurotransmitters across a gap between the cells called a synapse.

Think of this process like a relay race and the synapse as where the hand-off takes place. The sending neuron releases chemical neurotransmitters, which attach to specific receptors on the receiving neuron. Each type of chemical will attach to a different receptor. Once the chemical is on the receptor it can do one of three things:

  • Act as an agonist, causing it to excite whatever that receptors function is.
  • Act as a partial agonist, still exciting the receptor but not as efficiently and a full agonist.
  • Act as an antagonist, stopping the receptor’s function and blocking other chemicals from activating it.

This is the process that is primarily affected by drugs. Your body’s receptors exist to bind with naturally occurring neurotransmitters in the brain. However, drugs can either mimic existing chemicals and bind to the receptors themselves or affect the efficiency of naturally occurring chemicals. Psychoactive drugs can be a tremendous help in remedying chemical imbalances or relieving symptoms caused by neurochemical processes like pain. However, they can also cause problems if they are overused or abused.

Drug dependence happens when this chemical process is overexploited. If you take a psychoactive drug for too long or in excessive amounts, it could cause your brain to start to rely on the drug to maintain your neurochemical balance. It might stop producing certain natural chemicals that have the same effect as the drug or start producing other chemicals to counteract the drug.

If you suddenly start using smaller doses of the drug or stop using it all together, you will experience symptoms of withdrawal. This is when your brain chemistry suddenly becomes unbalanced, causing symptoms that can range from unpleasant to potentially deadly.

Finally, drug overdose occurs when your body is flooded with more of a drug than it can handle. Your body can handle some drugs in large amounts, like marijuana, without the threat of a fatal overdose. However, other substances like opioids can kill if you take much more than an appropriate dose.

How Opioids Work

Each class of psychoactive drugs works differently in the body, altering different chemicals and receptors and causing different effects. Opioids are relatively unique in that they actually bind to specific receptors in the brain, instead of altering the efficiency of naturally occurring chemicals. Opioids are derived from opium poppy plants with a natural alkaloid that acts as a psychedelic drug. But why is there a chemical inside a plant that binds perfectly to receptors in the human brain? Because your brain also produces its own opioids called endorphins. Endorphins are opioid receptor agonists that are designed to activate pain-relief effects, and they are also released when you’re feeling stressed.

Opioids do this to a much more efficient degree. They bind to receptors at the site of pain, in the spine where the pain is relayed to the brain, and in the brain itself. They hinder the pain signal from being sent by the sending neuron and stop the receiving neuron from getting the message. The result is euphoria, pain relief, relaxation, and the overall slowing down of your central nervous system.

Opioids can cause tolerance to develop, leading to chemical dependence. When they are used in excessive amounts, they can slow down your breathing to dangerous and deadly levels. Extremely powerful opioids have been synthesized that can be deadly even in tiny amounts. For instance, fentanyl is a synthetic opioid that can kill an average person if they take a dose the size of a snowflake.

How Depressants Work

Depressants are a class of drugs that includes prescription sleep-aids like benzodiazepines and alcohol. Depressants are GABAergic chemicals, which means they bind to gamma-Aminobutyric acid (GABA) receptors in the brain. GABA receptors are responsible for a wide variety of functions which includes reducing and managing excitability. Depressants are so named because of the way they suppress your nervous system causing anti-anxiety, sleep, and muscle relaxation.

Unfortunately, depressants have a high risk of causing chemical dependence. Even prescription depressants like benzos are usually not prescribed for consistent use for longer than four weeks. Alcohol has a high risk for addiction as well, and it’s often used as a method of self-medication, numbing painful emotional symptoms of psychological disorders like anxiety, depression, and trauma. However, depressants can make certain mental health issues worse by worsening existing chemical imbalances.

Once dependence on a depressant has developed, the subsequent withdrawal symptoms can be potentially dangerous, especially when trying to quit cold turkey. Dependence can cause a buildup of excitatory neurochemicals that are suppressed by the depressant. Stopping suddenly can cause over-excitement in the nervous system, leading to anxiety, panic, seizures, and delirium.

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How Stimulants Work

Stimulants are a class of drugs that excite the nervous system and cause feelings of energy, power, and euphoria. They have a variety of medical uses including treatments for obesity, mood disorders, sleep disorders, impulse control, and focus problems. The most popular medicinal stimulants are used to treat ADHD. However, the most common recreational stimulants are cocaine and methamphetamine.

Stimulants work by increasing the efficiency of dopamine, norepinephrine, and serotonin in the brain. These three neurochemicals are the main “feel-good” chemicals that play important roles in reward and motivation.

Cocaine blocks a process called reuptake which is when a chemical in the synapse is reabsorbed into the sending neuron when it is no longer needed. This process recycles the chemicals and stops it from binding to the receiving neuron in excess.

With cocaine in your system, a chemical like dopamine won’t be able to be reabsorbed, causing it to bind to more receptors.

Methamphetamines have similar effects to cocaine regarding reuptake, but they also cause more dopamine to be released.

This causes the synapse to flood with so much dopamine that excessive long-term use can actually damage the receptors.

With damaged receptors, it will be difficult for you to feel pleasure from anything except meth.

Abusing stimulants can cause psychosis, paranoia, and a variety of other adverse effects. They are highly addictive, sometimes causing users to binge on the drug for days. In withdrawal, the sudden lack of dopamine can cause a deep depression, sometimes leading to suicidal thoughts or actions.

Deeper Than The Nervous System

One of the most common side effects of recreational drugs like opioids, alcohol, and cocaine is addiction. Addiction is a disorder that goes a lot deeper than the brain’s messaging system. Addiction is a chronic disease that affects your reward and learning center. Excessive use of drugs that cause you to feel euphoric can trick your brain into believing that drug use is an activity that’s good for you or necessary to survive. The reward center is also called the limbic system, and it’s designed to help you identify good activities and encourage you to repeat them. This is why when you go to a new restaurant and try amazing new food, you always want to return to that place and to have it again.

The chemical rewards from pleasurable activities teach your brain to do them again. Drug use often causes powerfully pleasurable rewards, and your limbic system can’t tell the difference between using drugs and actual healthy rewarding activities.

Addiction is difficult to break, so difficult, in fact, that the National Institute of Drug Addiction defines addiction as “a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, despite harmful consequences.”

Treating Substance Use Disorders

If you or someone you know is struggling with a substance use disorder, it may quickly get out of control. Addiction may be a chronic disease, but it’s one that can be treated with professional service and individualized care. It’s not easy to overcome, but it’s nearly impossible to escape from the oppression of addiction on your own.


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StatPearls. (2020, May 21) Physiology, Neurotransmitters. Sheffer, Z., Reddy, V., Pillarisetty, L. Retrieved from

NIDA. (2020, May 29). Is there a difference between physical dependence and addiction?. Retrieved from

John Hopkins Medicine. Opioid Addiction. Retrieved from

ScienceDirect. (2009 January). Journal of Anxiety Disorders. Self-medication of anxiety disorders with alcohol and drugs: Results from a nationally representative sample. Robinson, J., et. al. Retrieved from

NIDA. (2020, July 13). Drug Misuse and Addiction. Retrieved from




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