Routes
ROUTES OF ADMINISTRATION
PSYCHOACTIVE SUBSTANCES ACT ON THE CENTRAL NERVOUS SYSTEM
Psychoactive substances are substances that can affect mood, perception, and behavior, and they act primarily on the central nervous system (CNS).
These substances are carried to the brain through the circulatory system.
Reinforcement of use is affected by:
The speed at which a substance enters the circulatory system.
The shorter the route to the brain, the more reinforced the use of the substance.
The combination of the onset speed of a substance's effects and the duration of those effects serves as a partial indicator of the potential for addiction to that substance.
BLOOD BRAIN BARRIER
The brain is protected by a structure known as the blood-brain barrier (BBB), which is composed of tightly sealed cells.
This barrier selectively permits certain substances to enter the brain while typically preventing toxins, viruses, and bacteria from crossing.
Most psychoactive substances are fat-soluble, which coincides with the brain’s fatty nature, granting these substances a preference for crossing the barrier.
The affinity of a substance for fat enhances its absorption speed into the brain. The greater the fat-solubility, the more rapid the absorption and subsequently intense the response elicited by the psychoactive substance.
ROUTES OF ADMINISTRATION
There are several main routes through which psychoactive substances can be administered:
Inhaling
Injecting
Snorting and mucosal exposure
Orally
Contact or Transdermal
INHALING
Inhalation involves vaporizing the substance and allowing it to be absorbed through the lungs into the bloodstream.
The process moves quickly from the lungs to the heart and then directly to the brain, making it the fastest delivery method, which takes about 7 to 10 seconds.
Users retain some capability to regulate the strength of the effect experienced.
Common substances administered through inhalation include:
Marijuana
Crack cocaine
Freebase cocaine
Nicotine
INJECTION
Injection is recognized as a very quick and potent method of delivering substances, leading to immediate effects.
Examples of substances administered via injection are:
Heroin
Cocaine
Methamphetamine
The intense rush experienced when substances are directly injected is a key characteristic.
There are three primary methods of injection:
Intravenous (IV) Injection:
Also known as slamming.
Direct delivery into the vein takes approximately 15-30 seconds for effects to be felt.
Intramuscular (IM) Injection:
Delivery involves injecting the substance into muscle mass.
Effects are usually felt within 3-5 minutes.
Subcutaneous Injection:
Referred to as “skin popping,” this method delivers the substance under the skin.
Effects also take around 3-5 minutes.
MUCOSAL ABSORPTION
Mucosal absorption involves the direct entry of substances through the mucous membranes into the bloodstream.
This delivery method is quicker because it bypasses the digestive system and its enzymes.
There are three principal methods of mucosal absorption:
Insufflation:
Inhalation through the nose.
Commonly associated with substances like cocaine and heroin.
Sublingual/Buccal Administration:
Administration occurs under the tongue or in the cheek pouch, examples include chewing tobacco or snuff.
Typically takes 3-5 minutes for effects to manifest.
Suppository Administration:
Involves inserting a substance rectally.
Utilized for medications like morphine for terminally ill patients, with effects taking 10-15 minutes.
INGESTING
Ingesting substances requires passage through the esophagus and stomach before entering the small intestines, where absorption into the bloodstream occurs.
After ingestion, substances must go through the liver for metabolism prior to reaching the heart and brain.
The ingestion process dilutes the substance due to the action of saliva, stomach enzymes, and liver processing, which generally results in a delayed effect.
Typically, the onset of effects is expected in about 20-30 minutes.
Examples of substances commonly ingested include:
Alcohol
Pills
TRANSDERMAL ABSORPTION
Transdermal absorption involves the administration of a substance via a patch applied to the skin.
This method provides a slow and sustained delivery of the substance into the bloodstream.
The duration of effect from transdermal administration can span from 1 to 7 days.
Common examples include nicotine patches and Fentanyl patches for pain management.
PSYCHOACTIVE SUBSTANCES ACT ON THE CENTRAL NERVOUS SYSTEM
Psychoactive substances are substances that can affect mood, perception, and behavior by interacting with specific receptors and altering neurotransmission within the central nervous system (CNS).
These substances are carried to the brain through the circulatory system, where they exert their effects.
Reinforcement of use is significantly affected by:
The speed at which a substance enters the circulatory system and reaches the brain.
The shorter the route and faster the onset to the brain, the more pronounced and immediate the reinforcing effects, thus increasing the potential for habitual use.
The combination of the onset speed of a substance's effects and the duration of those effects serves as a critical indicator of the potential for addiction to that substance; rapid onset coupled with short duration often correlates with higher abuse potential.
BLOOD BRAIN BARRIER
The brain is meticulously protected by a specialized structure known as the blood-brain barrier (BBB), which is composed of tightly sealed endothelial cells lining the brain's capillaries and further supported by astrocytes.
This barrier functions as a selective filter, permitting essential nutrients and certain substances to enter the brain while rigorously preventing toxins, viruses, bacteria, and many polar molecules from crossing, thereby maintaining a stable neural environment.
Most psychoactive substances are highly fat-soluble (lipophilic), which aligns with the brain’s high lipid content, granting these substances a preferential ability to traverse the barrier by diffusing directly through the cell membranes.
The affinity of a substance for fat greatly enhances its absorption speed into the brain. The greater the fat-solubility, the more rapid the absorption into brain tissue and subsequently more intense and immediate the psychoactive response elicited by the substance.
ROUTES OF ADMINISTRATION
There are several main routes through which psychoactive substances can be administered, each influencing the speed of onset, intensity, and duration of effects:
Inhaling
Injecting
Snorting and mucosal absorption
Orally
Contact or Transdermal
INHALING
Inhalation involves vaporizing the substance and allowing it to be absorbed rapidly through the vast surface area of the lungs' alveoli into the arterial bloodstream.
The process moves quickly from the lungs to the heart and then directly to the brain, making it the fastest delivery method, typically taking about 7 to 10 seconds for effects to manifest.
This rapid onset contributes to a powerful reinforcing effect. Users often retain some capability to regulate the strength of the effect experienced by controlling the depth and duration of inhalation.
Common substances administered through inhalation include:
Marijuana
Crack cocaine
Freebase cocaine
Nicotine
INJECTION
Injection is recognized as a very quick and potent method of delivering substances, leading to immediate and often intense effects due to the direct and concentrated delivery into the body's circulation.
The intense 'rush' experienced when substances are directly injected is a key characteristic, contributing to high abuse potential.
This route also carries significant health risks, including infections (e.g., HIV, hepatitis) from shared needles, vein damage, abscesses, and a higher risk of overdose due to the precise and often rapid delivery of concentrated doses.
Examples of substances commonly administered via injection are:
Heroin
Cocaine
Methamphetamine
There are three primary methods of injection:
Intravenous (IV) Injection:
Also known as slamming, this method involves direct delivery into a vein, introducing the substance immediately into the bloodstream.
Effects are usually felt within approximately 15-30 seconds, leading to the most rapid and intense onset among all injection methods.
Intramuscular (IM) Injection:
Delivery involves injecting the substance into muscle mass, which is less vascularized than veins but offers a steady absorption rate.
Effects are usually felt within 3-5 minutes, allowing for a somewhat slower onset compared to IV.
Subcutaneous Injection:
Referred to as “skin popping,” this method delivers the substance under the skin into the fatty tissue.
Effects also take around 3-5 minutes, similar to IM, but absorption can be less consistent and carries risks of local tissue damage and infection.
MUCOSAL ABSORPTION
Mucosal absorption involves the direct entry of substances through the highly vascularized mucous membranes into the bloodstream, bypassing the digestive tract and its associated first-pass metabolism.
This delivery method is quicker and allows for higher bioavailability compared to oral ingestion, as it bypasses the digestive system and its metabolizing enzymes in the liver.
There are three principal methods of mucosal absorption:
Insufflation (Snorting):
Involves inhaling the substance through the nose, where it is absorbed through the mucous membranes of the nasal passages which are rich in capillaries.
Commonly associated with substances like cocaine and heroin, effects are typically felt within minutes (around 2-5 minutes).
Sublingual/Buccal Administration:
Administration occurs under the tongue (sublingual) or in the cheek pouch (buccal), allowing for direct absorption into the systemic circulation through the capillaries in the mouth.
Examples include chewing tobacco or snuff, and certain medications like buprenorphine.
Typically takes 3-5 minutes for effects to manifest, avoiding initial liver metabolism.
Suppository Administration:
Involves inserting a substance rectally, where it can be absorbed through the rectal mucosa.
This method partially bypasses first-pass liver metabolism.
Utilized for medications like morphine for terminally ill patients, with effects typically taking 10-15 minutes to onset.
INGESTING
Ingesting substances requires passage through the esophagus and stomach before primarily entering the small intestines, where absorption into the bloodstream occurs.
After absorption, substances must first go through the liver for metabolism, a process known as 'first-pass metabolism,' which significantly breaks down a portion of the substance before it reaches the systemic circulation, heart, and brain.
The ingestion process dilutes and metabolizes the substance due to the action of saliva, stomach acids and enzymes, and liver processing, which generally results in a slower onset and reduced peak effects.
Typically, the onset of effects is expected in about 20-30 minutes, but this can vary widely based on factors such as stomach contents, gastric pH, and the specific substance.
Examples of substances commonly ingested include:
Alcohol
Pills (e.g., opioids, benzodiazepines)
TRANSDERMAL ABSORPTION
Transdermal absorption involves the administration of a substance via a patch applied to the skin, which is designed to allow the substance to slowly permeate the skin layers and enter the underlying capillaries.
This method provides a slow, controlled, and sustained delivery of the substance into the bloodstream, maintaining relatively constant plasma concentrations.
The duration of effect from transdermal administration can span from 1 to 7 days, offering convenience and consistent therapeutic levels while avoiding first-pass metabolism.
Common examples include nicotine patches for smoking cessation and Fentanyl patches for chronic pain management.