Effects of Drugs & Alcohol on the Nervous System

Nervous System Components & Functions

The nervous system consists of the brain, spinal cord, and the nerves outside of the brain and spinal cord. Traditionally, the human nervous system is divided into two major components:

1. The central nervous system: This consists of the brain and spinal cord.
2. The peripheral nervous system: This is the complete collection of nerves outside of the brain and spinal cord. The main function of this division of the nervous system is to connect the central nervous system to the rest of the body. The peripheral nervous system is typically divided up into two subdivisions:
   • The somato-sensory nervous system: This division of the peripheral nervous system is generally considered to be under the voluntary control of the person and includes nerves that are attached to skeletal muscles.
   • The autonomic nervous system: This is the part of the peripheral nervous system that is not generally considered to be under voluntary control. This system is further divided into two subdivisions: the sympathetic nervous system, which typically stimulates or speeds up functions in the body, and the parasympathetic nervous system, which typically slows down various functions.

The nerves that are part of the central nervous system are generally referred to as neurons, whereas outside the central nervous system, they are generally referred to simply as nerves. This system is a complex collection of nerves and other specialized cells that transmit signals throughout the body. One can think of it as the body’s system of electrical wiring, as neurons typically function through electrical and chemical activities.

Control of the nervous system is done mainly through the brain, and the spinal cord is used to transmit messages from the brain to different parts of the body and to receive information from different parts of the body. The nervous system has three general functions:

1. Receive input. Collect input from the environment or the body (sensory information).
2. Make sense of input. Interpret the sensory input (perception).
3. Act. Respond in an appropriate manner to the sensory inputs.

Responses to sensory input can consist of numerous actions depending on the specific division of the nervous system that is being utilized. Abuse of numerous drugs can have devastating effects on the nervous system, particularly the central nervous system. Because the brain is the master control unit for the entire sensory system and the rest of the body, the vast amount of research that is performed on the effects of drugs and alcohol on the nervous system is targeted at the effects of these substances on the brain.

Drugs That Can Alter the Brain

Most any drug can alter the brain in some manner. Certain drugs have chemical properties and mechanisms of action that make them more likely to produce significant alterations in the brain and to produce significant neurological issues for the person over time. While the list of these drugs is quite extensive, the major drugs that can seriously affect brain functioning include:

• Stimulants: central nervous system stimulants, such as cocaine and methamphetamine
• Depressants: central nervous system depressant drugs, particularly opiate drugs, benzodiazepines, and alcohol
• Inhalants: substances like aerosol sprays, paint thinner, and paint
• Hallucinogens: drugs that primarily produce hallucinations
• Nicotine: tobacco products can significantly alter brain functioning.
• Cannabis: many variations of cannabis products

Other drugs that do not neatly fit into the above categories can also significantly alter the brain, such as ecstasy (MDMA). Very often, so called designer drugs (drugs that are manufactured in private laboratories) contain substances that can be potentially toxic to the brain. These substances are not manufactured under strict guidelines or supervision by a governing body that is interested in the safety of the individuals using the drug.

The Effects of Long-Term Substance Abuse on the Central Nervous System

Different drugs of abuse may be more likely to produce specific effects on the brain. For instance, chronic use of powerful stimulants like cocaine is known to lead to an increased probability for hypertension, blockages of arteries, and cardiac issues. This can increase an individual’s risk for stroke. Chronic use of benzodiazepines affects other neurotransmitters (in addition to dopamine) that can affect a person’s ability to learn and remember new information.

Although most drugs of abuse do affect the functioning of the availability of dopamine to some extent, different classes of drugs will affect different neurotransmitters, which will lead to structural changes in the pathways of the brain that primarily use those neurotransmitters (in addition to the reward pathway). For example, chronic use of some drugs may be more likely to produce problems with attention and concentration that can interfere with the memory process, whereas other drugs may not affect the attention and concentration of the person significantly, but may affect the memory process of encoding and retrieving material.

Neuroplasticity & Drug Use

Neuroplasticity is simply a term that describes the remarkable ability of the brain to alter its structure and functioning in response to the experiences one has. Research has identified the plasticity of the brain, and there have been decades of research investigating how the brain changes in response to the experiences of the person. This feature of the brain has been a significant part of how researchers understand the functions of the brain and the development of human behavior.

Many of the alterations that occur in the brains of individuals who abuse drugs and alcohol are alterations that represent the plasticity of the brain. Other changes may be due to the toxic effects of the drugs themselves.

The notion that specific changes occur in everyone or that there is a “one-size-fits-all” rule, such that individuals who use any specific drug will develop specific issues is not well substantiated by the research. Other influences besides the use of drugs will come into play in everyone, and there will be significant variation in how each individual responds to the use of drugs or alcohol. These influences include genetics, past experience, the type of drug being used, the amount and frequency of use, and the effects of other experiences.

Treatment & Outlook

The ability of the brain to repair itself is limited, particularly in adults. Individuals who have long-term issues with substance abuse may experience some resolution to cognitive, emotional, or other problems that are believed to be due to brain damage, but some individuals may continue to experience issues with different areas of functioning. In most cases, the best way to address the neurological effects associated with a substance use disorder is to remain abstinent from drugs and alcohol, stay in recovery, and remain in recovery for years.