What is a Drug?

Broadly speaking, a drug is any chemical substance that, when introduced into the body, alters its function either physically or psychologically. This is different from food, which primarily provides nutrition. Drugs interact with the body's complex systems, often targeting specific mechanisms to produce their effects.

Now, let's break down how these substances impact the human body, step-by-step:

1. Entry & Distribution:
   • Drugs enter the body through various routes: ingestion (swallowing), inhalation (smoking/snorting), injection (intravenous/intramuscular), or absorption (skin patches).
   • Once in, they enter the bloodstream, which acts like a highway, transporting the drug molecules throughout the body, including across the blood-brain barrier to reach the brain. The speed of onset depends heavily on the route (injection is fastest, ingestion is often slowest).
2. The Brain - The Main Target:
   • Most drugs exert their main effects by interfering with the brain's communication system. Neurons (nerve cells) communicate using chemical messengers called neurotransmitters (like dopamine, serotonin, GABA, norepinephrine, endorphins).
   • Drugs hijack this system in a few ways:
     li>Mimicking: Some drugs have structures similar to natural neurotransmitters and can activate neurons (e.g., opioids mimic endorphins, binding to opioid receptors causing pain relief and euphoria).
     • Blocking Reuptake: Some prevent neurotransmitters from being recycled back into the neuron that released them, leading to a buildup in the synapse (the gap between neurons) and amplifying their effect (e.g., cocaine blocks dopamine reuptake, causing a surge in pleasure/reward signals).
     • Altering Release: Some cause neurons to release abnormally large amounts of neurotransmitters (e.g., amphetamines trigger excessive dopamine release).
     • Blocking Receptors: Some block neurotransmitters from binding to their receptors, dampening signals (e.g., certain antipsychotics block dopamine receptors).
3. Immediate Effects (Short-Term):
   • This neurotransmitter disruption causes the immediate, noticeable effects. These vary widely depending on the drug class:
     • Stimulants (e.g., Cocaine, Amphetamines, Caffeine): Increase alertness, attention, energy, heart rate, blood pressure. They primarily boost dopamine and norepinephrine.
     • Depressants (e.g., Alcohol, Benzodiazepines, Barbiturates, Opioids): Slow down brain function, induce relaxation, drowsiness, reduce anxiety, slow breathing and heart rate. They often enhance the effect of GABA (an inhibitory neurotransmitter) or act on opioid receptors.
     • Hallucinogens (e.g., LSD, Psilocybin): Drastically alter perception, thoughts, and feelings. Often interfere with serotonin pathways.
     • Cannabinoids (e.g., Marijuana): Complex effects, often relaxation, altered perception, increased appetite. Interact with the body's own endocannabinoid system.
4. Systemic Effects (Beyond the Brain - Short Term):
   • Cardiovascular: Changes in heart rate and blood pressure (up with stimulants, down with depressants). Risk of irregular heartbeat.
   • Respiratory: Slowed breathing (depressants, especially opioids - risk of overdose), or sometimes rapid breathing (stimulants).
   • Thermoregulation: Body temperature can increase (stimulants like MDMA) or decrease.
   • Other: Nausea, dizziness, coordination problems, changes in appetite.
5. Metabolism & Elimination:
   • The body works to break down (metabolize) the drug, primarily in the liver, into inactive components (metabolites).
   • These metabolites are then filtered out by the kidneys and eliminated, mostly through urine.
   • The duration of a drug's effect depends on how quickly it's absorbed, distributed, and metabolized/eliminated.
6. Long-Term Effects & Consequences:
   • Tolerance: With repeated use, the brain adapts. More of the drug is needed to achieve the same effect.
   • Dependence: The body adapts to the drug's presence and experiences physical or psychological withdrawal symptoms when the drug is stopped (e.g., anxiety, tremors, pain, nausea).
   • Addiction: A chronic, relapsing brain disease characterized by compulsive drug seeking and use despite harmful consequences. This involves profound changes in brain circuits related to reward, stress, and self-control.
   • Organ Damage: Chronic use can damage organs like the liver (alcohol, inhalants), heart (cocaine, stimulants), lungs (smoking anything), kidneys, and brain (neurotoxicity from various drugs).
   • Mental Health: Can trigger or worsen mental health conditions like depression, anxiety, psychosis.
   • Overall Health: Weakened immune system, increased risk of infections (especially with injection), malnutrition.

Summary Table

Written by Parthipan Kasiban