What is cannabis

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cannabis overview pharmacology uses effects 2025

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Here is a thorough overview of cannabis, drawing from authoritative medical textbooks:

Cannabis (Marijuana)

What Is It?

Cannabis is one of the most widely used psychoactive substances on Earth, with an estimated 182.5 million users (3.8% of the global population). It is derived from the Cannabis sativa and Cannabis indica plants, which contain over 100 alkaloid cannabinoids and hundreds of chemical compounds. - Essentials of Forensic Medicine and Toxicology, 36th ed. (2026)

The Three Main Varieties

Variety	Height	Features	Region
Cannabis sativa	1-4 m	Loosely branched, coarse stem, 3-7 toothed leaves	Far East, UK, USA
Cannabis indica	~1.2 m	Dwarf, densely branched, larger leaves	India
Cannabis ruderalis	30-60 cm	Unbranched/sparsely branched, largest leaves	-

Active Ingredient: THC

The primary psychoactive compound is delta-9-tetrahydrocannabinol (THC). It makes up up to 4-5% of the plant's composition and is most concentrated in the bracts, leaves, and flowers. When cannabis is smoked, approximately 5-10% of the THC content is absorbed. - Robbins & Kumar Basic Pathology

The other major compound is cannabidiol (CBD), an isomer of THC that is relatively inactive at cannabinoid receptors and has no psychoactive properties. Higher CBD content lowers the risk of hallucinations, delusions, and memory impairment - and pure CBD may even be antipsychotic and anxiolytic. - Stahl's Essential Psychopharmacology

How It Works: The Endocannabinoid System

The brain produces its own cannabis-like neurotransmitters - anandamide and 2-arachidonoyl glycerol (2-AG) - which act on cannabinoid receptors CB1 and CB2. THC mimics these endogenous neurotransmitters. CB1 receptors are densely distributed in the brain; CB2 receptors are also found in peripheral immune cells. - Stahl's Essential Psychopharmacology

Acute Effects

In normal intoxicating doses, cannabis produces:

Sense of well-being and relaxation
Feeling of friendliness
Loss of temporal awareness (confusing past with present)
Slowed thought processes
Impaired short-term memory
Feeling of achieving special insights

At high doses, it can cause panic, toxic delirium, and psychosis - especially in vulnerable individuals. - Stahl's Essential Psychopharmacology

Medical Uses

Nausea/vomiting - synthetic oral cannabinoid (dronabinol) is FDA-approved for chemotherapy-induced nausea and AIDS-related anorexia
Glaucoma - smoked cannabis reduces intraocular pressure
Pain relief - THC has analgesic properties used in conditions like cancer and intermittent claudication
Appetite stimulation - cannabis is a known appetite enhancer ("the munchies")
Mood elevation - used as an anxiolytic and mood stabilizer

Essentials of Forensic Medicine and Toxicology (2026)

Cardiovascular and Pulmonary Effects

Cannabis shares many carcinogens and lung irritants with tobacco, but chronic use has not been definitively shown to impair pulmonary function or increase lung cancer incidence
Lung consequences include: cough, chest tightness, bronchitis, airway inflammation, and bronchodilation
Acutely, it increases sympathetic activity and decreases parasympathetic activity, raising cardiac output - which may cause orthostatic hypotension
No strong evidence currently links cannabis use to myocardial infarction or stroke
Robbins & Kumar Basic Pathology

Mental Health Risks

Over time, cannabis has become more potent - higher THC, lower CBD - increasing the risk of hallucinations, delusions, anxiety, and memory impairment. Long-term heavy use is associated with "amotivational syndrome" (apathy, loss of drive). Cannabis can also precipitate or exacerbate schizophrenia in vulnerable individuals; one study found that eliminating high-potency cannabis use would prevent 12% of first-episode psychosis cases across Europe. - Stahl's Essential Psychopharmacology

Legal Status (as of 2022, USA)

38 US states + DC: legal for medical use
18 US states + DC: legal for recreational use
Still federally illegal under US law

Forms of consumption: Smoking, vaporizing, edibles, oils, tinctures, and topicals.

FDA-approved cannabinoid drugs: Dronabinol (for nausea/anorexia), Nabilone (for chemotherapy nausea), and Cannabidiol/Epidiolex (for certain epilepsy syndromes).

Post transitional stage and pre transitional stage relate to hypertension

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pre-transitional post-transitional stage hypertension socioeconomic epidemiology Park

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I have all I need from the key Park's passage. Here is the full explanation:

Pre-Transitional vs. Post-Transitional Stages and Hypertension

This concept comes from the field of epidemiology and social medicine, specifically the relationship between socio-economic status (SES) and hypertension across different stages of economic and epidemiological development.

The Core Concept

The prevalence pattern of hypertension in a population reverses depending on the country's stage of economic and epidemiological transition. - Park's Textbook of Preventive and Social Medicine

Post-Transitional Stage

What it is: Countries that have already undergone full economic and epidemiological development - i.e., developed/industrialized nations (e.g., USA, UK, most of Western Europe). These societies have largely moved past infectious diseases as the main cause of death, and chronic non-communicable diseases (CVD, diabetes, hypertension) dominate.

Hypertension pattern:

"In countries that are in the post-transitional stage of economic and epidemiological change, consistently higher levels of blood pressure have been noted in lower socio-economic groups."

This inverse relationship is seen across all three indices of SES:

Lower education → higher BP
Lower income → higher BP
Lower occupational status → higher BP

Why? In post-transitional societies, the poor bear the greatest burden of unhealthy behaviors and environments - poor diet, obesity, stress, less access to healthcare, sedentary lifestyle, smoking, and alcohol misuse.

Pre-Transitional Stage

What it is: Countries or societies that are still developing or in early economic transition - i.e., low- and middle-income countries (LMICs) still dominated by infectious disease burden, subsistence economies, and limited urbanization.

Hypertension pattern:

"In societies that are transitional or pre-transitional, a higher prevalence of hypertension have been noted in upper socio-economic groups."

Why? In these societies, the wealthy are the first to adopt:

High-calorie, high-fat "Western" diets
Sedentary/office-based lifestyles
Access to alcohol and processed food
Urban living with its associated stressors

The poor in these societies tend to do more physical labor, eat simpler diets, and are less exposed to the cardiovascular risk factors that accompany wealth and urbanization at this early stage.

The Reversal: What It Means

Stage	Hypertension Burden Falls On	Reason
Pre-transitional (developing)	Upper socioeconomic group	Wealthy adopt Western diet/lifestyle first
Post-transitional (developed)	Lower socioeconomic group	Poor face cumulative risk - poor diet, stress, less healthcare

"This probably represents the initial stage of the epidemic of CVD."

Park's Textbook of Preventive and Social Medicine, p. 426

Clinical & Public Health Significance

This reversal is a marker of where a society sits on the epidemiological transition curve
As developing countries urbanize and transition economically, the burden of hypertension gradually shifts from rich to poor - mirroring the pattern already seen in developed countries
This has major implications for targeted public health strategies: in pre-transitional societies, interventions should initially target affluent urban populations; in post-transitional societies, they must focus on disadvantaged communities

What are the stages of epidemiological transition in detail?

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stages of epidemiological transition Omran pestilence famine degenerative man-made diseases detail

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I now have comprehensive content for a detailed answer. Here it is:

The Stages of Epidemiological Transition

The epidemiological transition describes the transformation in the causes of morbidity and mortality that occurs as populations industrialize and urbanize. It was first described by Abdel Omran in 1971 and later expanded upon by Olshansky and Ault (1988). The shift is driven by industrialization, urbanization, and associated lifestyle and demographic changes - and is occurring in all parts of the world, across all races and cultures. - Harrison's Principles of Internal Medicine, 22nd ed. (2025)

There are 5 stages, though the original model had 3, later expanded to 4, and now a 5th emerging stage is recognized.

Stage 1: Age of Pestilence and Famine

Characteristic: Predominance of malnutrition and infectious diseases as causes of death.

High rates of infant and child mortality
High fertility rates (to offset high death rates)
Mean life expectancy: ~30 years
Major killers: tuberculosis, dysentery, cholera, influenza
CVD accounts for <10% of deaths
CVD type seen: Rheumatic heart disease and cardiomyopathies caused by infections and malnutrition
Economy is largely agrarian

Example: United States before 1900; most of sub-Saharan Africa historically.

Stage 2: Age of Receding Pandemics

Characteristic: Emergence of public health systems, cleaner water, and improved nutrition drive down infectious disease deaths.

Infant and childhood mortality decline sharply
Per capita income and life expectancy begin to rise
CVD deaths rise to 10-35% of all deaths
CVD types seen: Rheumatic valvular disease, hypertension, CHD, and stroke (predominantly hemorrhagic)
Almost 40% of the world's population is currently in this stage

Key insight: Hypertension starts emerging as a burden, particularly in upper socioeconomic groups (the pre-transitional pattern discussed previously).

Example: USA in the 1930s; much of South Asia and sub-Saharan Africa today.

Stage 3: Age of Degenerative and Man-Made Diseases

Characteristic: Non-communicable diseases overtake infectious diseases and malnutrition as the dominant cause of death.

Caloric intake increases, especially from animal fat
Physical activity declines with urbanization
Average life expectancy surpasses 50 years
CVD accounts for 35-65% of all deaths
CHD and stroke are prevalent; CHD:stroke ratio = 2:1 to 3:1
Hypertension and atherosclerosis become major risk factors
Roughly 35% of the world's population is in this stage

Example: USA between 1930-1965; much of Latin America, parts of Eastern Europe today.

Stage 4: Age of Delayed Degenerative Diseases

Characteristic: CVD and cancer remain the major causes of death, but age-adjusted CVD mortality begins to decline.

CVD still accounts for ~40% of all deaths, but occurring at older ages
Preventive strategies take effect: smoking cessation, blood pressure control
Improved acute hospital management (bypass surgery, thrombolytics, etc.)
Primary forms: CHD, stroke, and congestive heart failure
Age at first CVD event steadily rises
About 15% of the world's population is now in this stage or transitioning out of it

Example: USA between 1965-2000; most of Western Europe, Australia, Japan.

Stage 5: Age of Inactivity and Obesity (Emerging)

Characteristic: Physical activity continues to decline while total caloric intake rises - producing an epidemic of overweight and obesity.

Rising rates of type 2 diabetes, hypertension, and lipid abnormalities - especially in children
After decades of decline, age-adjusted CVD mortality rates have begun to rise again in recent years
The decline in CVD death rates of ~3% per year seen in the 1970s-80s has tapered to ~2% and has even reversed
In 2020 and 2021, there was an increase in CVD mortality not seen since the early 1960s

Example: USA currently; emerging in many middle-income countries.

Summary Table

Stage	Key Feature	Life Expectancy	CVD Deaths	Dominant CVD Type
1. Pestilence & Famine	Infection & malnutrition dominant	~30 years	<10%	Rheumatic HD, infective cardiomyopathy
2. Receding Pandemics	Public health improvements, falling infections	Rising	10-35%	Rheumatic valvular, hypertension, stroke (hemorrhagic)
3. Degenerative & Man-made	NCDs overtake infections	>50 years	35-65%	CHD and stroke (CHD:stroke 2-3:1)
4. Delayed Degenerative	CVD delayed to old age by prevention	High	~40%	CHD, stroke, heart failure
5. Inactivity & Obesity	Obesity epidemic, rising NCD burden in youth	Plateauing	Rising again	Metabolic CVD, T2DM-related CVD

Relationship to Hypertension (Connecting to the Previous Discussion)

Transition Stage	Hypertension Prevalence Pattern
Pre-transitional (Stage 1-2)	Higher in upper socioeconomic groups (wealthy adopt Western lifestyle first)
Post-transitional (Stage 3-4)	Higher in lower socioeconomic groups (poor bear cumulative risk burden)

As Park's Textbook notes, this reversal "probably represents the initial stage of the epidemic of CVD" - making it a useful marker for where a society sits on the transition curve.

Harrison's Principles of Internal Medicine, 22nd ed. (2025)
Park's Textbook of Preventive and Social Medicine

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