Drug Effects on the Brain - Quick Reference

Drug action basics

• Drugs alter brain communication by affecting neurons and synapses.
• Agonist vs antagonist: agonists activate receptors by mimicking neurotransmitters; antagonists block or dampen receptor activity.
• Caffeine is an antagonist of adenosine receptors.
• Repeated drug use can rewire neural networks, affecting thinking, decisions, learning, and memory.

How drugs reach the brain

• Must reach the bloodstream; speed depends on administration: oral (slowest), inhalation (faster), intravenous (fastest).
• Blood-brain barrier (BBB) protects the brain; drug molecules must have chemical properties that allow entry.

Neurons and synapses

• Neurons have a nucleus, dendrites, and an axon.
• Synapses are contact points that allow exchange of electrochemical signals between neurons.
• Neurotransmitters carry signals and can be inhibitory or excitatory.

Neurotransmitter lifecycle and drug effects

• Leftover neurotransmitters are degraded or reabsorbed (reuptake).
• Drugs alter synaptic transmission by affecting production, release, receptor binding, reuptake, or degradation, increasing or decreasing neurotransmitter activity.

Examples: medicines

• SSRIs: block reuptake of serotonin to increase its levels in neural networks.
• Morphine: can raise levels of serotonin and noradrenaline and engage endorphin systems to reduce pain and alter mood/energy.
• Tranquilizers: increase GABA production to inhibit neural activity, promoting relaxation.

Illicit drugs and mechanisms

• Methamphetamine/amphetamine: induce long-lasting dopamine release and activate noradrenaline receptors, boosting arousal and fight/flight responses.
• Cocaine: blocks reuptake of dopamine and serotonin, increasing signaling and producing energy and euphoria.
• Hallucinogens (LSD, mescaline, DMT): disrupt serotonin signaling and affect neural circuits involved in perception, learning, and behavior regulation.

Why drugs are controlled or illegal

• Drugs can permanently alter brain chemistry with repeated use, affecting thinking, decision-making, learning, and memory.
• Ongoing research aims to understand benefits and risks to develop medicines and therapies.

Takeaway

• Core idea: drugs modify brain signaling by altering neurotransmitter dynamics and receptor activity; access to the brain depends on administration route and BBB crossing; medicines and illicit drugs share this basic mechanism but differ in safety and legality.