How should cannabis or THC be taken to treat asthma?
(British Medical Association):
Acute doses of cannabis and THC exert a definitive bronchodilator effect on the small airways of the lungs. The mechanism of this effect is not known, but it appears to be different from that of other drugs used at present as bronchodilators for asthma. (…) However, there have been very few studies on the bronchodilator effects of cannabinoids in asthmatic patients. All of these were studies carried out in the 1970s. Tashkin et al. studied 14 asthmatic volunteers and compared smoked cannabis (2%THC), oral THC (15mg) and the drug isoprenaline (0.5%). They found that smoked cannabis and oral THC produced significant bronchodilatation of at least two hours duration. The effect of smoked cannabis was nearly equivalent to the clinical dose of isoprenaline. Smoked cannabis was also capable of reversing experimentally induced bronchospasm in three asthmatic subjects. (…) Williams et al. compared a THC aerosol containing 0.2 mg THC with a salbutamol aerosol (0.1 mg) in 10 asthmatic subjects. Both drugs significantly improved respiratory function. The onset of effect was more rapid with salbutamol, but the effects of both drugs were equivalent at one hour. Tashkin et al. compared several doses of THC aerosol (5-20mg) with a standard dose of isoprenaline in 11 normal volunteers and five asthmatic subjects. In the normal subjects and three of the asthmatics, the bronchodilator effect of THC was less than that of isoprenaline after five minutes, but significantly greater after one to three hours.
(Please note: This text has been taken from a scientific article. Some sentences have been changed to improve understandability.)
British Medical Association: Therapeutic Uses of Cannabis. Amsterdam: Harwood Academic Publishers, 1997.
The treatment of asthma includes the use of anti-inflammatory drugs (corticosteroids) and bronchodilators. THC and cannabis are bronchodilators and may also exert some anti-inflammatory and anti-allergic action. Cannabis smoke contains combustion products qualitatively similar to those found in tobacco smoke, among them several carcinogens that may damage the mucosa. The inhalation of these combustion products should be avoided or strongly decreased. To avoid the intake of combustion products cannabis can be taken orally. To decrease the amount of inhaled carcinogens cannabis or THC can be inhaled by a vaporizer, and/or cannabis with a high THC content can be used/smoked. In several situations, a combination of a basic oral medication and a demand inhaled medication in acute asthma attacks may be useful to reduce the risks from smoking and the risk of overdosage with oral administration. The availability of a THC aerosol is desirable.
(Calignano and colleagues):
An international research group has discovered why marijuana causes coughing in some situations but may inhibit bronchospasm and cough in others. This finding could lead to better treatments of respiratory diseases. In a report in the journal Nature scientists from the Institute of Experimental Medicine in Budapest (Hungary), the University of Naples (Italy) and the University of Washington (USA) showed how the endocannabinoid anandamide influences the airways in the lungs. In animal studies with guinea pigs and rats, anandamide exerted a dual effect on bronchial responsiveness. If the muscles in the lungs were constricted by an irritant (capsaicin) the endocannabinoid relaxed the smooth muscles and strongly inhibited coughing. But if the airways were relaxed (by removing the constricting effect of the vagus nerve) anandamide caused a coughing spasm. Anandamide is synthesized in lung tissues and its effects are mediated by cannabinoid receptors. (…)
IACM-Bulletin of 12 November 2000; Calignano A, et al: Bidirectional control by airway responsiveness by endogenous cannabinoids. Nature 2000;408:96-101.