Marijuana and Lung Diseases

Manish Joshi; Anita Joshi; Thaddeus Bartter

Disclosures

Curr Opin Pulm Med. 2014;20(2):173-179. 

In This Article

Abstract and Introduction

Abstract

Purpose of review Cannabis sativa (marijuana) is used throughout the world, and its use is increasing. In much of the world, marijuana is illicit. While inhalation of smoke generated by igniting dried components of the plant is the most common way marijuana is used, there is concern over potential adverse lung effects. The purpose of this review is to highlight recent studies that explore the impact upon the respiratory system of inhaling marijuana smoke.

Recent findings Smoking marijuana is associated with chronic bronchitis symptoms and large airway inflammation. Occasional use of marijuana with low cumulative use is not a risk factor for the development of chronic obstructive pulmonary disease. The heavy use of marijuana alone may lead to airflow obstruction. The immuno-histopathologic and epidemiologic evidence in marijuana users suggests biological plausibility of marijuana smoking as a risk for the development of lung cancer; at present, it has been difficult to conclusively link marijuana smoking and cancer development.

Summary There is unequivocal evidence that habitual or regular marijuana smoking is not harmless. A caution against regular heavy marijuana usage is prudent. The medicinal use of marijuana is likely not harmful to lungs in low cumulative doses, but the dose limit needs to be defined. Recreational use is not the same as medicinal use and should be discouraged.

Introduction

Marijuana has been used by man for over 3000 years.[1–3] It has been used by multiple civilizations. Its uses have ranged from utilitarian (rope) to medicinal to religious. In the United States, marijuana was used medicinally until 1941, when it was dropped from the United States Pharmacopeia.[1–3] The Controlled Substances Act passed in 1970 classified marijuana as a schedule 1 drug, defined by the Drug Enforcement Administration as follows (http://www.justice.gov/dea/druginfo/ds.shtml): 'Schedule I drugs, substances, or chemicals are defined as drugs with no currently accepted medical use and a high potential for abuse. Schedule I drugs are the most dangerous drugs of all the drug schedules with potentially severe psychological or physical dependence'. This definition persists to this day.

Marijuana is the most commonly used illicit substance worldwide. Globally, the estimated prevalence of marijuana users in 2011 was 180.6 million or 3.9% of the adult population aged 15–64 years.[4] Though the United States, Australia and New Zealand reported the highest prevalence of cannabis use, it is produced and consumed in virtually every country and territory of the world.[4] Marijuana is derived from the cannabis plant belonging to the Cannabaceae family.[4,5] It is prepared from the dried flowering tops and leaves of the female plant.[4,5] Combustion of marijuana produces hundreds of substances. The main psychoactive ingredient in marijuana is delta-9-tetrahydrocannabinol (THC); however, more than 60 compounds (cannabinoids) have been identified within the cannabis plant.[5,6] An endogenous cannabinoid (endocannabinoid or eCB) system is a recently discovered signaling system comprising the cannabinoid CB1 and CB2 receptors.[5]

The most common route of marijuana use is by inhalation of smoke. Smoke is usually inhaled from compacted and rolled leaves, analogous to a cigarette (a 'joint'), or from a water pipe ('bong').[6] Most studies quantify exposure to cannabis smoke as 'joint-years'; one joint-year is equivalent to one joint smoked daily for a year. When marijuana is smoked, THC is absorbed into the bloodstream via the lungs.[6,7] Marijuana smoke contains a complex mixture of chemicals qualitatively similar to tobacco smoke with the exception of nicotine, which is unique to tobacco.[8,9] As it shares similar compounds with tobacco smoke, increasing widespread use of marijuana smoking raises concerns for short and long-term respiratory complications including bronchitis, pneumothorax/pneumomediastinum and chronic lung diseases like chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD) and lung cancers. This review highlights the recent studies that explore the use of marijuana and its impact on the respiratory system. There are direct implications for both recreational and medical use of marijuana.

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