5.13 Effects of Drug Use and Tolerance
Long Term Effects of Drug Use
Overview of Long Term Effects
Drug use can lead to both short-term and long-term effects.
Long term effects are significant and often differ from short-term effects.
Tolerance
Definition: Tolerance is a phenomenon where increasing dosages of a drug are needed to achieve the same psychological effect.
This shift is represented graphically where the y-axis shows the drug's effect (from no high to a significant high) and the x-axis shows the drug dose (from small to large doses).
Example: Caffeine is a common substance that exhibits tolerance.
Initial consumption of a small amount results in significant stimulation, while seasoned drinkers require multiple cups for the same energy boost.
Mechanisms of Tolerance:
Metabolic and Cellular Tolerance: Refers to biological changes in the cells that improve their efficiency in eliminating the drug.
Example: Alcoholics exhibit increased amounts of smooth endoplasmic reticulum in their cells, enhancing their ability to detoxify alcohol.
Changes in Receptor Levels: Extended drug use can lead to down-regulation of neuroreceptors in the brain.
Mechanism of Down-Regulation:
Neurons aim to maintain a consistent activity level (normal action potentials).
Drug-induced excessive neurotransmitter release (e.g., dopamine) leads to neuron overactivity.
To counter this overstimulation, neurons reduce the number of available receptors, limiting neurotransmitter binding and thus reducing the effect of the drug over time.
Consequences of Receptor Down-Regulation:
If a person stops using the drug after prolonged use, they may struggle to activate these affected neurons, leading to an inability to experience normal feelings of happiness and potentially resulting in relapse due to feeling down or depressed.
Dependence
Physical Dependence: This occurs when the body becomes accustomed to a drug, leading to adverse symptoms upon its cessation.
withdrawal symptoms can include: nausea, headaches, vomiting, delirium, and hallucinations.
Coffee withdrawal may result in headaches and lethargy, illustrating a mild form of physical dependence.
Psychological Dependence:
Psychological factors often lead to the initial use of drugs, typically in response to negative emotions.
Individuals may relapse if they encounter stress or reminders of the traumatic circumstances that led to their initial drug use.
Social aspects of drug use (e.g., cigarettes) can also perpetuate dependence.
For example, social smoking can create a sense of belonging that users may miss if they quit.
Expectations and Drug Use
The way drugs are perceived can significantly influence their effects.
For instance, users often report stronger effects after repeated use due to the development of expectations regarding the drug's effects.
Placebo-like effects can augment the perceived efficacy of a drug based on prior experiences.
Context Dependent Overdoses
Definition: Occurs when drug users experience fatal overdoses in unfamiliar environments where the body lacks anticipatory responses to the drug.
Mechanism: Anticipatory drug responses are conditioned based on previous experiences, which help mitigate the drug's impact.
If drugs are consumed in a novel setting, the absence of environmental cues leads to increased risk of overdose.
Experiment with Rats:
A study illustrated this phenomenon by administering heroin to two groups of rats: one group in a familiar environment and the other in a novel setting.
Results showed a higher mortality rate in the group administered heroin in the unfamiliar context, demonstrating the risk associated with context-dependent responses.
Example of Physiological Response:
Heroin typically slows heart rate; however, in familiar contexts, users may experience increased heart rate due to conditioning, providing a compensatory effect against the drug's depressive effects on the heart.
In novel contexts, the anticipatory response is absent, leading to life-threatening bradycardia (extremely low heart rate).
Real-World Application:
Celebrities often overdosing while in unfamiliar places may illustrate the unpredictability of drug effects in new contexts.
Minor changes in drug use rituals or methods can also heighten overdose risks.