11.3 Psychoactive drugs and their effects on the brain
4 min read•august 14, 2024
Psychoactive drugs alter brain function, causing changes in perception, mood, and behavior. These substances interact with neurotransmitter systems, mimicking or modifying their actions. Understanding their mechanisms helps explain both their therapeutic potential and risks.
From that boost alertness to that induce relaxation, each drug category affects the brain differently. Long-term use can lead to lasting changes in brain structure and function, highlighting the importance of responsible use and medical supervision.
Categories of psychoactive drugs
Stimulants, depressants, opioids, hallucinogens, and cannabis
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- Psychoactive drugs are substances that alter brain function, leading to temporary changes in perception, mood, consciousness, and behavior
- Major categories include:
- Stimulants (cocaine, amphetamines) increase alertness, attention, and energy by enhancing the activity of and neurotransmitter systems in the brain
- Depressants (alcohol, benzodiazepines, barbiturates) reduce anxiety, induce sleep, and slow down brain activity by increasing the effects of the neurotransmitter and reducing excitatory neurotransmission
- (heroin, morphine, prescription painkillers) produce feelings of and pain relief by activating opioid receptors in the brain, primarily in regions involved in reward processing and pain modulation
- (LSD, psilocybin) cause altered perceptions, thoughts, and emotions by acting on receptors in the brain, particularly the 5-HT2A receptor subtype
- (marijuana, synthetic cannabinoids) produces relaxation, altered sensory experiences, and impaired memory by activating cannabinoid receptors (CB1 and CB2) in the brain
Mechanisms of psychoactive drugs
Interactions with neurotransmitter systems
- Psychoactive drugs exert their effects by interacting with specific neurotransmitter systems in the brain
- Mimic the actions of endogenous neurotransmitters
- Block neurotransmitter reuptake
- Alter neurotransmitter production or release
- Stimulants (cocaine, amphetamines) increase dopamine and norepinephrine levels by:
- Blocking their reuptake transporters (DAT and NET)
- Promoting their release from presynaptic terminals
- Leads to enhanced signaling in reward and arousal pathways
- Depressants (alcohol, benzodiazepines) enhance the activity of the inhibitory neurotransmitter GABA by:
- Binding to GABA receptors (particularly GABA-A)
- Increasing their responsiveness to GABA
- Results in reduced neuronal excitability and anxiety
- Opioids bind to and activate opioid receptors (mu, delta, and kappa) in the brain
- Mimic the actions of endogenous opioid peptides (endorphins, enkephalins)
- Leads to reduced pain perception and increased dopamine release in reward circuits
- Hallucinogens (LSD, psilocybin) act as agonists at serotonin 5-HT2A receptors
- Leads to altered sensory processing, perceptual changes, and mystical-type experiences
- Cannabis compounds () bind to and activate cannabinoid receptors (CB1 and CB2)
- Modulates the release of various neurotransmitters (GABA, glutamate, dopamine)
- Results in altered cognition, memory, and mood
Effects of drugs on brain
Short-term effects on brain function
- Acute changes in neurotransmitter levels, receptor activation, and alterations in neuronal firing patterns
- Leads to the desired psychological and behavioral effects
Long-term adaptations in brain structure and function
- Chronic use of psychoactive drugs can lead to long-lasting changes:
- Receptor density
- Neurotransmitter production and release
- Synaptic plasticity
- Stimulant use can cause:
- Dopamine depletion
- Reduced dopamine receptor availability in the brain's reward system
- Contributes to anhedonia, craving, and addiction
- Long-term alcohol use can result in:
- Neurodegeneration, particularly in the frontal lobes and hippocampus
- Impairments in executive function, memory, and emotional regulation
- Chronic opioid use can lead to adaptations in the brain's pain and reward systems
- Reduced sensitivity to natural rewards
- Increased sensitivity to pain (hyperalgesia)
- Contributes to the development of and dependence
- Hallucinogen use, particularly chronic use, may cause:
- Persistent perceptual disturbances (HPPD)
- Alterations in brain network connectivity
- Long-term effects are not well understood
- Regular cannabis use, especially when initiated during adolescence, can:
- Impair cognitive function, particularly memory and attention
- Increase the risk of developing psychiatric disorders in vulnerable individuals
Therapeutic uses vs risks
Potential therapeutic applications for mental health disorders
- Some psychoactive drugs, when used under medical supervision, can be effective treatments for various mental health disorders
- Depression
- Anxiety
- PTSD
- Substance use disorders
- Stimulants (methylphenidate, amphetamines) are used to treat attention-deficit/hyperactivity disorder (ADHD)
- Enhance dopamine and norepinephrine signaling in the prefrontal cortex
- Improve attention and reduce impulsivity
- Antidepressants (SSRIs, TCAs) are used to treat depression and anxiety disorders
- Increase the availability of serotonin and/or norepinephrine in the brain
- Benzodiazepines are prescribed for short-term treatment of anxiety disorders and insomnia
- Rapid anxiolytic and sedative effects mediated by GABA-A receptor activation
- Opioid agonists (methadone, buprenorphine) are used in (MAT) for opioid use disorder
- Reduce symptoms and craving
- Block the effects of illicit opioids
- Ketamine, an NMDA receptor , has shown rapid antidepressant effects in treatment-resistant depression
- Long-term safety and efficacy remain under investigation
- Psychedelic-assisted psychotherapy (psilocybin, MDMA) is being explored as a potential treatment for:
- Depression
- Anxiety
- PTSD
- Substance use disorders
- Promising initial results
Risks associated with the use of psychoactive drugs
- The use of psychoactive drugs in treating mental health disorders also carries risks:
- Side effects
- Drug interactions
- Dependence
- Potential for abuse
- Necessitates careful monitoring and individualized treatment plans
Key Terms to Review (26)
Agonist: An agonist is a substance that binds to a receptor and activates it to produce a biological response. These molecules mimic the action of naturally occurring neurotransmitters, enhancing or facilitating their effects in the nervous system. By doing so, agonists play crucial roles in various physiological processes and are integral in understanding how different drugs interact with neural pathways.
Animal models: Animal models are living organisms, often non-human animals, used in research to study biological processes, disease mechanisms, and the effects of treatments. They are essential for understanding complex brain functions and behaviors, providing insights that are difficult to achieve through other methods such as human studies or cell cultures.
Antagonist: An antagonist is a substance that binds to a receptor and inhibits or blocks its activity, preventing the natural ligand from eliciting a biological response. By interfering with receptor activation, antagonists play crucial roles in pharmacology and neuropharmacology, as they can modulate various physiological processes and behaviors by counteracting the effects of agonists.
Cannabis: Cannabis is a plant that contains psychoactive compounds, primarily tetrahydrocannabinol (THC) and cannabidiol (CBD), which can produce various effects on the brain and body when consumed. Often used recreationally and medicinally, cannabis interacts with the endocannabinoid system, impacting mood, appetite, pain sensation, and memory.
Cross-dependence: Cross-dependence refers to a phenomenon where the effects of one psychoactive drug can influence the use or effects of another drug. This interaction often occurs when two drugs act on similar neurotransmitter systems in the brain, leading to enhanced or diminished effects when taken together. Understanding cross-dependence is essential for comprehending how different substances can impact each other and contribute to the overall experience and risks associated with poly-drug use.
Decriminalization: Decriminalization refers to the process of reducing or eliminating criminal penalties associated with certain behaviors or activities, typically regarding the use of psychoactive substances. This approach shifts the focus from punishment to regulation, often aiming to address public health issues rather than legal ones. In the context of psychoactive drugs, decriminalization can lead to more effective treatment options and harm reduction strategies, changing societal perceptions and responses to drug use.
Depressants: Depressants are a class of psychoactive drugs that reduce neural activity and slow down body functions. These substances can affect mood, perception, and behavior by enhancing the effects of the neurotransmitter gamma-aminobutyric acid (GABA), leading to a calming effect on the brain. Depressants are commonly used to treat anxiety, insomnia, and other related conditions, but they can also be misused and lead to dependence.
Dopamine: Dopamine is a neurotransmitter that plays several important roles in the brain, influencing mood, motivation, reward, and motor control. It is critical in many neural pathways, connecting various brain regions and affecting behavior and cognitive functions.
Euphoria: Euphoria is a profound sense of happiness or well-being that can be triggered by various stimuli, including psychoactive substances. It often involves intense feelings of joy, excitement, or elation and can significantly influence behavior and motivation. Understanding euphoria is essential in the context of how different drugs can induce these feelings through their effects on brain chemistry and the mechanisms that underlie their action.
Functional MRI: Functional MRI (fMRI) is a neuroimaging technique that measures and maps brain activity by detecting changes in blood flow and oxygen levels. This non-invasive method allows researchers and clinicians to observe brain functions in real-time, making it essential for understanding various neural processes related to cognition, emotion, and motor control.
GABA: GABA, or gamma-aminobutyric acid, is the primary inhibitory neurotransmitter in the brain that plays a crucial role in reducing neuronal excitability throughout the nervous system. It helps maintain a balance between excitatory and inhibitory signals, influencing various functions such as mood, motor control, and cognitive processes.
Hallucinogens: Hallucinogens are a class of psychoactive drugs that cause significant alterations in perception, mood, and cognitive processes, often leading to experiences of visual or auditory hallucinations. These substances can profoundly affect how an individual perceives reality, altering sensory experiences and emotional states. They can be derived from natural sources or synthesized in laboratories, impacting neurotransmitter systems in the brain, particularly those involving serotonin.
Harm reduction: Harm reduction refers to a set of strategies aimed at minimizing the negative health, social, and legal impacts associated with drug use. This approach recognizes that while substance use can pose significant risks, completely eliminating drug use may not be feasible for everyone. Instead, harm reduction seeks to reduce the harmful consequences of drug use through various means, including education, access to clean needles, and safe consumption spaces, which all connect deeply with understanding drug categories, their mechanisms of action, and the brain's response to psychoactive substances as well as addiction and substance abuse disorders.
Medication-assisted treatment: Medication-assisted treatment (MAT) is a therapeutic approach that combines medications with counseling and behavioral therapies to treat substance use disorders, particularly opioid addiction. By using specific medications, MAT helps to reduce withdrawal symptoms and cravings, making it easier for individuals to focus on their recovery. This approach recognizes that addiction is a complex condition requiring comprehensive treatment strategies that address both the biological and psychological aspects of dependence.
Mesolimbic system: The mesolimbic system is a pathway in the brain that plays a crucial role in the processing of rewards and reinforcement. It connects the ventral tegmental area (VTA) to the nucleus accumbens, and is heavily involved in the response to pleasurable stimuli, such as food, social interactions, and drugs. This system is particularly important when discussing how psychoactive drugs can impact mood, motivation, and behavior by altering the normal function of reward pathways.
Norepinephrine: Norepinephrine is a neurotransmitter and hormone that plays a critical role in the body's response to stress and in regulating mood, attention, and arousal. It acts primarily in the brain and the peripheral nervous system, influencing various physiological functions, such as heart rate and blood pressure, while also impacting cognitive processes like focus and emotional responses.
Opioids: Opioids are a class of drugs that include both natural and synthetic compounds that bind to opioid receptors in the brain, producing pain-relieving effects. These substances are often used medically to manage pain but can also lead to significant addiction and misuse. Understanding their mechanisms of action is crucial for recognizing their impact on the brain and behavior.
Psychopharmacology: Psychopharmacology is the study of how drugs affect the mind and behavior, focusing on the interactions between psychoactive substances and the nervous system. This field examines how various drugs influence mood, perception, cognition, and overall mental functioning, providing insights into both therapeutic applications and potential abuses. Understanding psychopharmacology helps to clarify the complex relationship between pharmacological agents and neurobiological mechanisms in the brain.
Reuptake inhibition: Reuptake inhibition refers to the process where a substance, typically a drug, prevents the reabsorption of neurotransmitters into the presynaptic neuron after they have been released into the synaptic cleft. This leads to an increased concentration of neurotransmitters in the synaptic cleft, enhancing their effects on postsynaptic receptors. Reuptake inhibition plays a critical role in the action of many psychoactive drugs, influencing mood, perception, and behavior.
Reward Pathway: The reward pathway is a neural circuit in the brain that reinforces behaviors by providing pleasurable feelings in response to stimuli or actions that are considered rewarding. This pathway is crucial for motivation, reinforcement learning, and addiction, as it highlights the connection between behavior and pleasure, particularly in relation to the effects of psychoactive drugs.
Serotonin: Serotonin is a neurotransmitter that plays a key role in regulating mood, emotions, and various physiological processes in the body. It's involved in functions like sleep, appetite, and digestion, and is often linked to feelings of well-being and happiness.
Stimulants: Stimulants are a class of psychoactive drugs that increase activity in the central nervous system, leading to heightened alertness, increased energy, and improved mood. These substances can enhance cognitive function and physical performance but also come with potential risks, including addiction and adverse health effects. Understanding stimulants is crucial when discussing their impact on the brain and overall mental health.
Substance use disorder: Substance use disorder is a complex condition characterized by an individual's inability to control their use of psychoactive substances, leading to significant impairment or distress. It encompasses various patterns of substance consumption, resulting in adverse consequences on health, social life, and daily functioning. This disorder is closely linked to the effects of psychoactive drugs on the brain, highlighting how these substances can alter neurotransmitter systems and contribute to addictive behaviors.
THC: THC, or tetrahydrocannabinol, is the main psychoactive compound found in cannabis that produces the 'high' associated with marijuana use. It interacts primarily with the endocannabinoid system in the brain, influencing various physiological processes and affecting mood, memory, and appetite. Understanding THC is crucial for grasping how psychoactive drugs can alter brain function and behavior.
Tolerance: Tolerance refers to the body's decreased response to a drug after repeated use, requiring higher doses to achieve the same effect. This phenomenon occurs due to physiological adaptations in the brain and body, impacting how drugs interact with receptors and neurotransmitter systems over time. Understanding tolerance is crucial in examining how different drug categories work and their various mechanisms of action, as well as recognizing the profound effects of psychoactive substances on brain function.
Withdrawal: Withdrawal refers to the physical and psychological symptoms that occur when a person reduces or stops the intake of a substance they have become dependent on. This process can result in a range of unpleasant effects, highlighting the body's adaptation to the presence of drugs, especially in cases of prolonged use. The severity and nature of withdrawal symptoms can vary based on the substance involved, the duration of use, and individual differences in metabolism and neurochemistry.