PMC

Although many methods to inhale cannabis are well known, in recent years some older methods have gained increasing popularity (eg, hookah), and a number of new methods to inhale cannabis have emerged (eg, dabbing). These methods involve either inhaling combusted product or inhaling vaporized, noncombusted products (eg, G-pen). Rationales for an individual choice are highlighted in , along with potential harms and disadvantages associated with the method.

A, B, Laboratory investigations have historically ascribed a number of effects associated with habitual use of cannabis, particularly when it is used daily or for many years. A, Effects of inhaled cannabis on the upper airway feature increased mucous production and impaired mucociliary clearance that symptomatically correlate with increased cough and phlegm production reported by cannabis smokers.^, The presence of CB₁ receptors on terminal axons that innervate airways smooth muscle are believed to be responsible for the acute bronchodilatory effects associated with inhaled cannabis. Premalignant lesions described with cannabis use include squamous metaplasia, an increased nuclear-to-cytoplasmic ratio, increased Ki-67 antigen, and increased epidermal growth factor receptor expression. B, In the alveoli, inhaled cannabis has been associated with increased numbers of alveolar macrophages. Moreover, the normal function of these cells may be impaired due to cannabis-CB₂ receptor interactions,^‐ further contributing to symptoms of chronic bronchitis reported by long-term cannabis users. However, the literature does not unequivocally support an increased incidence of pneumonia among long-term cannabis users. Airway lymphocytes (not shown) also possess CB₂ receptors, but cannabinoid receptors have not been described on neutrophils. CB = cannabinoid; NOS = nitric oxide synthase.