Jennings, A.L., Davies, A.N., Higgins, J.P., Gibbs, J.S., & Broadley, K.E. (2002). A systematic review of the use of opioids in the management of dyspnoea. Thorax, 57(11), 939–944.
 

This systematic review included trials of opioids for the treatment of dyspnea secondary to any cause.

Eighteen randomized, double-blind, placebo-controlled crossover trials were evaluated. Meta-analyses were performed on all included studies and on various subgroups (e.g., nebulized opioids).

Patient populations were mixed, with 2 of the 18 trials including patients with a cancer diagnosis only and one of the 18 trials including patients with cancer with other advanced diseases.

A strong effect of non-nebulized opioids relative to placebo in reducing breathlessness was found. The subgroup analysis failed to show a positive effect of nebulized opioids on the sensation of breathlessness. Evidence supports the use of oral and parenteral opioids to treat dyspnea and argues against the use of nebulized opioids.

All but one study had a small sample size (n = 6–18 subjects); cancer-related dyspnea was included but was not a main focus of the research.