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Most people will take a pill,

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receive an injection,

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or otherwise take some kind of medicine
during their lives,

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but most of us don't know anything
about how these substances actually work.

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How can various compounds impact the way
we physically feel,

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think,

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and even behave?

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For the most part, this depends on
how a drug alters the communication

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between cells in the brain.

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There are a number of different ways
that can happen.

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But before it gets into the brain,

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any drug must first reach the bloodstream

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on a journey that can take anywhere
from seconds to hours,

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depending on factors like how
it's administered.

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The slowest method is to take
a drug orally

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because it must be absorbed by
our digestive system

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before it takes effect.

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Inhaling a drug gets it into
the bloodstream faster.

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And injecting a drug intravenously
works quickly too

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because it pumps the chemicals directly
into the blood.

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Once there, the drug quickly reaches
the gates of its destination, the brain.

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The entrance to this organ is guarded
by the blood-brain barrier,

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which separates blood 
from the nervous system

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to keep potentially dangerous 
substances out.

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So all drugs must have a specific
chemical composition

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which gives them the key to unlock
this barrier and pass through.

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Once inside, drugs start to interfere
with the brain's normal functioning

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by targeting its web of neurons 
and synapses.

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Neurons are brain cells that have
a nucleus, dendrites, and an axon.

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Synapses are structures placed along
the dendrites or the axon

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which allow the exchange of 
electrochemical signals between neurons.

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Those signals take the form of chemicals
called neurotransmitters.

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Each neurotransmitter plays different
roles in regulating our behaviors,

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emotions,

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and cognition.

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But they all work in one of two ways.

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They can either inhibit 
the receiving neuron,

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limiting its activity,

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or excite it,

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creating a new electrochemical signal
that spreads throughout the network.

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Any leftover neurotransmitter usually
gets degraded

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or reabsorbed 
into the transmitting neuron.

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A drug's effectiveness stems 
from its ability

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to manipulate these synaptic transmissions
at different phases of the process.

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That results in an increase or a decrease

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in the amount of neurotransmitters
being spread.

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For instance, common antidepressants,
like SSRIs,

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stop the reabsorption of serotonin,

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a neurotransmitter that modulates
our moods.

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This effectively pushes more of it
into the neural network.

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Meanwhile, painkillers, like morphine,

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raise levels of serotonin 
and noradrenaline,

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which regulate energy,

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arousal,

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alertness,

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and pleasure.

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Those same neurotransmitters also
affect endorphin receptors,

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reducing pain perception.

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And tranquilizers works by increasing
the production of GABA

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to inhibit neural activity

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putting the person in a relaxed
or sedated state.

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What about illegal or elicit drugs?

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These have powerful impacts on the brain
that we're still trying to understand.

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Crystal meth, an amphetamine,

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induces a long-lasting release
of dopamine,

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a neurotransmitter linked with
the perception of reward and pleasure.

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It also activates noradrenaline receptors,

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which increases the heart rate,

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dilates pupils,

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and triggers the body's fight
or flight response.

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Cocaine blocks the reuptake of dopamine
and serotonin,

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pushing more into the network

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where they boost energy,

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create feelings of euphoria,

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and suppress appetites.

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And hallucinogenic drugs have some
of the most puzzling effects.

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Substances like LSD,

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mescaline,

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and DMT

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all block the release of serotonin,

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which regulates mood and impulsivity.

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They also have an impact 
on the neural circuits

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involved in perception, learning,
and behavioral regulation,

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which may explain why these drugs
have such powerful impacts.

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Even if some of these 
effects sound exciting,

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there are reasons why some of these drugs
are highly controlled and often illegal.

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Drugs have the power to alter 
the brain's chemistry,

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and repeated use can permanently
rewire the neural networks

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that support our ability to think,

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make decisions,

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learn,

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and remember things.

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There's a lot we still don't know 
about drugs and their effects,

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both the good and the bad.

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But those we do know about are the ones
we've studied closely,

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and turned into effective medicines.

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As our knowledge grows about drugs
and the brain,

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the possibilities will also increase

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for treating the many medical problems
that puzzle researchers today.