Amphetamines are a class of psychostimulant drugs that accelerate the transmission of messages between the brain and the body. While some forms are prescribed by doctors to treat conditions like Attention Deficit Hyperactivity Disorder (ADHD), they are also frequently produced and used illicitly, carrying a significant potential for abuse.

Amphetamines

As a result of drug tolerance, some users of amphetamine would take large doses to experience a "high". From this, these users would develop symptoms of paranoia (auditory hallucinations, bizarre motor behavior, etc), which closely resembled schizophrenic symptoms.

Not only that, but amphetamine worsens symptoms of schizophrenia. Amphetamine is found to promote the release of dopamine and prolong the action of the released transmitter by blocking reuptake.

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All of the early antipsychotics were found to block postsynaptic dopamine receptors, particularly D2 receptors. From this, researchers proposed the dopamine hypothesis.


Origins of the Dopamine Hypothesis of Antipsychotics

A condition in which, with repeated exposure to a drug, an individual becomes less responsive to a constant dose. 
 
- Metabolic tolerance 
- Functional tolerance 
- Behavioral Tolerance
- Cross-tolerance 
- Withdrawal symptoms
- Sensitization 


Drug tolerance

Reuptake is a specific mechanism for clearing the synapse where excess neurotransmitters are pumped back into the presynaptic neuron that originally released them. By returning neurotransmitters to fill synaptic vesicles, this process signals to the cell that no additional neurotransmitters need to be manufactured, thereby helping to regulate overall neurotransmitter production.

Reuptake

A process in which the body shows an enhanced response to a given drug after repeated doses

Drug sensitization

- Greater drug doses tend to produce greater effects
- This relationship is shown in dose-response curves

Dose Response Relationship 

- Pattern of substance use that lasts more than one month but does not meet the criteria for dependence 
- 21.6 million Americans suffer from substance-related disorder in 2013 

Drug/Substance Abuse 

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Drug Abuse as Support of the Dopamine Hypothesis of Antipsychotic Drugs

The form of drug tolerance that arises when repeated exposure to the drug causes the metabolic machinery of the body to become more efficient at clearing the drug.

Metabolic tolerance

Decreased responding to a drug after repeated exposures, generally as a consequence of up- or down- regulation of receptors. 

Functional tolerance

A condition in which the development of tolerance for one drug causes and individual to develop tolerance for another drug. 

Cross tolerance

An uncomfortable symptom that arises when a person stops taking a drug that he or she has used frequently, especially at high doses.

Withdrawal symptoms

The body learns to rapidly down-regulate the function of a specific neurotransmitter when environmental cues for the drug are present. This decreases the effect of the drug on the body. Overdoses are more likely to occur when environmental cues are not present, since body does not down-regulate the receptors for this drug. 

Behavioral Tolerance/ Environment Dependent Tolerance

Cocaine acts as an agonist in the dopamine neurotransmitter system by blocking dopamine reuptake at the neuronal synapse.

Cocaine's Mechanism of Action

- A plot of the drug's effect versus the dose 
- Used to assess important drug characteristics 
- One of the main tools for understanding pharmacodynamics 

Dose Response Curve 

Opioid Use Disorder Library

- Substance use disorder
- Chronic and complex neurobiological disease 
- Associated with frequent relapse of taking drugs
- Major public health issue 
- Craving is a main component of OUD and other substance use
disorders

Opioid Use Disorder (OUD)

These are items used to prepare and inject opioids. As depicted in the image, examples include a tourniquet, syringes, cotton balls, a small cooking vessel like a spoon, a condom, sterile water, and an alcohol swab for cleaning the injection site.

Drug Paraphernalia for Intravenous Opioid Use

Data on drug use prevalence reveals distinct patterns across different age demographics, with young adulthood (ages 18-25) representing a peak period for the use of most substances. 

*   **Illicit Drugs:** Use is highest at approximately 22% for the 18-25 age group, compared to 10% for ages 12-17 and 7% for those 26 and older.
*   **Marijuana:** Follows a similar trend, with 18% prevalence in the 18-25 group, 7.5% in the 12-17 group, and 5% in the 26 and older group.
*   **Psychotherapeutics:** Usage peaks at 6% for ages 18-25, with lower rates of 3% for ages 12-17 and 2.5% for those 26 and older.
*   **Hallucinogens and Cocaine:** Use is also highest in the 18-25 age group (approximately 2.5% and 2% respectively) and significantly lower in other age brackets.
*   **Inhalants:** This category is an exception, with the highest prevalence among the youngest group (1% for ages 12-17), which then declines with age.

Prevalence of Drug Use by Age Group

A method of drug administration where heroin is injected directly into a vein using a hypodermic needle. The image provided shows this act being performed on an ankle.

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