Marijuana is the most widely used illicit drug in the Western world and the third most commonly used recreational drug after alcohol and tobacco. According to the World Health Organization, it also is the illicit substance most widely cultivated, trafficked, and used.

Although the long-term clinical outcome of marijuana use disorder may be less severe than other commonly used substances, it is by no means a “safe” drug. Sustained marijuana use can have negative impacts on the brain as well as the body. Studies have indicated a link between regular marijuana use and schizophrenia as well as a demonstrated relationship between marijuana use and a higher incidence of lung cancer.

Although there are no pharmacological treatments available with a proven impact on marijuana use disorder, there are several types of behavior therapy that may be effective in treating this disorder.

What is Marijuana?

Marijuana is an illicit psychoactive sedative drug from the cannabis (hemp) plant. The name marijuana is thought to have its origins in the Portuguese word mariguango, which translates as intoxicant. Marijuana consists of the dried and crushed leaves from the cannabis plant, which are typically smoked, but can also be eaten in baked goods or consumed as tea. In the United States, marijuana is typically smoked in rolled cigarettes (“joints”), in pipes or water pipes, or in hollowed-out cigars (“blunts”).

Marijuana is known by many names including pot, reefer, grass, weed, and many others. People’s experiences with marijuana can differ considerably depending on the potency of the drug. Many users experience sedative effects such as relaxation and drowsiness.

The psychoactive chemical in marijuana is delta-9-tetrahydrocannabinol (delta-9-THC or THC). THC is also the active ingredient in several FDA approved medications such as dranabinol and nabilone. These medications are used to treat medical conditions including glaucoma, severe nausea, vomiting, weight loss, and pain.

The Marijuana Plant The cannabis (hemp) plant, Cannabis sativa, is the source of marijuana and hashish. The cannabis plant contains more than 400 chemicals. At least 60 of the chemicals are cannabinoids (as they bind to cannabinoid receptors in the brain), but the most important of these cannabinoids is delta-9-tetrahydrocannabinol (THC). Delta-9- tetrahydrocannabinol is the plant’s main psychoactive chemical, although researchers are examining some of the other chemicals found in this plant for potential additional medicinal use. Various marijuana plants can significantly differ in how much THC is contained in each. Marijuana can contain 1% to 3% THC all the way up to 25%.


The absorption of THC depends primarily on the mode of consumption. The most rapid and efficient absorption of marijuana occurs through smoking. Inhalation results in absorption directly through the lungs, and the onset of the THC action begins within minutes. Assessments of blood plasma reveal that peak concentrations occur 30 to 60 minutes later. The drug effects can be experienced for two to four hours.

Oral ingestion of marijuana is much slower and relatively inefficient. The onset of action is longer than when smoked, taking as long as an hour. The marijuana is absorbed primarily through the gastrointestinal tract, and peak plasma levels can be delayed for as long as two to three hours following ingestion.

An important difference from absorption through smoking is that blood containing orally ingested marijuana goes through the liver before going to the brain. The liver processes or clears much of the THC so that lesser amounts have the opportunity to exert action in the brain; however, the drug effects following oral ingestion can be experienced for longer periods of time, generally four to six hours. The dose needed to create a comparable high when orally ingested is estimated as three times greater than that needed when smoking.

Cannabis Intoxication

Cannabis intoxication, a cannabis-related disorder coded as 292.89, is defined by DSM-5, as the following:

  • Recent use of cannabis
  • Clinically significant problematic behavioral or psychological changes (i.e., impaired motor coordination, euphoria, anxiety, sensation of slowed time, impaired judgment, social withdrawal) that developed during, or shortly after, cannabis use
  • At least 2 of the following signs, developing within 2 hours of cannabis use:
  • Conjunctival injection
  • Increased appetite
  • Dry mouth
  • Tachycardia

Respiratory Effects of Marijuana

The impact of chronic marijuana smoking on respiratory health has many similarities to that of tobacco smoking. Compared with nonsmokers, chronic marijuana smokers show increased likelihood of outpatient visits due to respiratory illness and exhibit respiratory symptoms of bronchitis at comparable rates to tobacco smokers. Chronic bronchitis can be moderately debilitating and increases the risk of additional infections.

As THC appears to suppress immune system function, recurrent bronchitis may further increase the risk of opportunistic respiratory infections such as pneumonia and aspergillosis. This is of concern particularly for those individuals with already compromised immune functions such as cancer and AIDS patients.

Airway obstruction and symptoms of chronic cough, sputum production, shortness of breath, and wheezing characterize chronic bronchitis. These symptoms are the result of airway inflammation and tissue damage caused by marijuana smoke that results in increased fluid production, cellular abnormalities, and reduced alveolar permeability. This damage begins long before overt symptoms such as cough or wheezing are evident. Cellular abnormalities include reductions in ciliating surface cells of the lungs that function to clear fluid from the lungs to the mouth and throat. As a result, marijuana smokers have substantially higher bronchitis index scores than nonsmokers, and comparable scores to tobacco smokers, even at young ages with only short histories of marijuana use. Investigations of chronic obstructive pulmonary disease (COPD) in chronic marijuana smokers have been inconclusive.

A common severe consequence of tobacco smoking, COPD includes chronic obstructive bronchitis or emphysema, and is characterized by impairment in small airway function rather than large airways.

Marijuana smokers exhibit almost identical degrees of histopathologic and molecular abnormalities associated with progression to COPD in tobacco smokers and several case reports have been identified. However, two earlier large-scale studies of COPD in chronic marijuana users have been inconclusive.

Chronic cannabis smoking is likely associated with respiratory cancer, although this link is not definitive. Cannabis smoking is clearly associated with similar processes and patterns of disease that lead to aerodigestive cancers among tobacco smokers. As noted previously, marijuana smoke contains more carcinogens than cigarette smoke. Marijuana interferes with normal cell function, including synthesis and functions of DNA and RNA, and appears to activate an enzyme that converts inactive carcinogens found in marijuana smoke into active carcinogens. Chronic marijuana smokers also show substantial cellular mutation associated with tumor progression.

Marijuana also reduces the ability of pulmonary alveolar macrophages to kill pathogens, including tumor cells, allowing tumors to grow more rapidly. Clinical reports of aerodigestive cancers in individuals who had a history of marijuana smoking with limited or no tobacco exposure have provided suggestive evidence of a link between marijuana use and cancer.

In addition, Zhang, et al., (1999) found increased risk for squamous-cell carcinoma of the head and neck for marijuana smokers compared with nonsmokers when tobacco smoking was statistically controlled. Similarly in a case-controlled hospital study in Casablanca, Morocco, Sasco, et al., (2002) found that the use of hashish was independently predictive of lung cancer.

The only epidemiological study that directly examined the risk of aerodigestive cancer in marijuana users reported no significant risk associated with cannabis. This study, however, included a relatively young cohort comprised of primarily experimental and light marijuana users rather than chronic heavy users.

Individuals who began smoking marijuana in the late 1960s are now approaching ages that are more likely to be associated with aerodigestive cancer; hence, future epidemiological studies should clarify better the risk of cancer associated with chronic cannabis use. Smoking both cannabis and tobacco warrants mention as this combination most likely produces an additive adverse effect on the respiratory system.

Tobacco smoking is common among cannabis users, as almost half of daily marijuana users also smoke tobacco. This subgroup of marijuana smokers merits careful study as they may be at particularly high risk for respiratory disease.

Request Appointment