Never done it personally, but here is what the Martindale says... FWIW
"The pharmacokinetics of inhaled diamorphine fumes ("chasing the dragon") has been studied in diamorphine addicts receiving substitution therapy with diamorphine and methadone. Absorption through the lungs occurred very rapidly and was virtually complete immediately after inhalation; bioavailability was estimated to be about 53%.
1. Kendall JM, Latter VS. Intranasal diamorphine as an alternative to intramuscular morphine: pharmacokinetic and pharmacodynamic aspects. Clin Pharmacokinet 2003; 42: 501–13. 2. Rook EJ, et al. Population pharmacokinetics of heroin and its major metabolites. Clin Pharmacokinet 2006; 45: 401–17"