Funding for this research was provided by:
National Institute on Drug Abuse (DA037820)
Received: 8 March 2018
Accepted: 29 April 2018
First Online: 16 May 2018
Ethics approval and consent to participate
: The University of California, San Francisco IRB approved this research study. All participants provided oral consent at the time of the interview.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.