Drugs and the Nervous System: Use, Effects, and Dependence

Drug

Any substance, natural or artificial, other than food, that by its nature alters structure or function in a living organism.

Psychoactive drugs

Drugs that specifically affect thoughts, emotions, and behavior.

Drug use

When an organism actively takes a drug into its body to produce an effect.

Drug abuse

Using a drug in a manner that causes problems or greatly increases the chance of problems occurring.

Drug taking behavior

Can be defined as use or abuse, independent of the drug itself.

Specific effects

The effects of a drug that result from direct interaction with the body.

Dose-response relationships

Effects are dependent on dosage; all drugs have multiple effects.

Nonspecific effects

The effects of a drug do not depend solely on how the drug interacts with the body; experience, expectation (belief), and setting play a role.

Placebo effects

Especially important in treating pain and depression; a review of data on the 12 most popular antidepressants revealed that 80% of the effectiveness of the drugs was due to placebo.

Dependence

Consistent and frequent use of a drug, along with difficulty if use of the drug were discontinued.

Withdrawal

Discontinuation of drug use produces characteristic physiological experiences that are relieved by administration of the drug.

Physiological Dependence

Sometimes called Physical Dependence.

Cravings

An experience of 'wanting' a drug and behavior that seeks to acquire the drug.

Psychological Dependence

Sometimes called Behavioral Dependence.

Early explanations of dependence

Focused on withdrawal symptoms; dependence was all about removing withdrawal symptoms.

New data on dependence

Suggests that cravings and drug-seeking behavior are key.

Alcohol

Produced by the metabolic process of fermentation; metabolism of sugars without oxygen to produce energy.

Anaerobic metabolism

Requires water; certain yeasts will ferment sugars and produce alcohol.

Sugar source for fermentation

Fruits have sugars readily available; grains must have starches converted to sugars by adding malt.

Ethanol

The active compound in alcoholic drinks; a depressant.

Mechanism of action of ethanol

Ethanol is an agonist of GABAA receptors and has low affinity for glutamate receptors, acting as an antagonist.

Cell membranes and ethanol

May also make cell membranes 'leaky', increasing permeability to all ions.

Ethanol

Produces dosage-dependent effects, similar to depressants.

Low dose of alcohol

Reduced anxiety, sleepiness, motor coordination difficulties, sociability/lack of inhibitions, aggression in some individuals.

Moderate dose of alcohol

Increased sleepiness, major motor coordination difficulties, may induce sleep but individual still responsive to external stimuli, inhibition of memory formation.

High dose of alcohol

Induced sleep without response to external stimuli, coma, respiratory arrest.

Alcohol use sensitivity

Particularly sensitive to non-specific (placebo) effects because of the strong expectations we have from our culture.

Physiological effects of ethanol

Prevents blood clotting, causes vasodilation of peripheral blood vessels, makes you feel warm but increases heat loss from core, decreases vasopressin release, increases urine production, lowers blood pressure, increases stress hormone release, decreased sex hormone release.

Alcohol-related deaths

20,000 deaths/year from behavioral causes like car accidents and violent crime; 1,000 deaths/year from respiratory arrest (alcohol poisoning).

Dependence potential of ethanol

Has a high dependence potential as it indirectly activates the reward and reinforcement system.

Withdrawal symptoms from alcohol

Can be severe and cause death, including tremors, rapid heartbeat, hypertension, insomnia, hallucinations, delusions, disorientation (delirium tremens), and seizures.

Marijuana

Made from the leaves and flowers of plants in the Cannabis genus.

Active ingredients in marijuana

Concentrated in resins released from the plant.

Cannabinoids

A class of compounds unique to marijuana, with at least 70 known cannabinoids including cannabinol, cannabidiol, cannabigerol, and 9-delta-tetrahydrocannabinol (THC).

THC

Most pharmacologically active cannabinoid and a partial agonist of the cannabinoid receptors (CB1 & CB2).

CB1 receptors

Found in the brain and regulate memory, feeding behavior, and motor function.

CB2 receptors

Found in immune cells of the body and regulate immune function.

Effects of THC via CB1 receptors

Includes euphoria (nucleus accumbens), motor coordination difficulties (cerebellum), reduced verbal communication and increased appreciation of humor (cerebral cortex), and reduced short-term memory function (hippocampus).

Marijuana use history

In the 1960's marijuana use became a symbol of rejection of authority and peaked in the 1970's.

Marijuana overdose

Not a concern, but those with cardiovascular risks are at increased risk for heart attack/stroke.

Marijuana smoking risks

Likely damages lungs and contains many of the same known carcinogens as tobacco smoke.

Dependence potential of marijuana

Has a moderate dependence potential, with higher numbers of people seeking help for dependency than all drugs except alcohol and opioids.