Funding for this research was provided by:
National Institute on Drug Abuse (R01DA022582)
First Online: 1 March 2019
Compliance with ethical standards
: Author Lopez declares that he has no conflict of interest. Author Heatherton declares that he has no conflict of interest. Author Wagner declares that he has no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
: Informed consent was obtained from all individual participants included in the study.