**2.2 Literature search**

The databases PsycInfo, PubMed, and PTSDPubs were searched to identify studies of interest. Each search was conducted using a Boolean search logic and relevant keywords: ("PTSD" OR "post traumatic stress disorder" OR "posttraumatic stress disorder" OR "post-traumatic stress disorder" OR "trauma") AND ("cue" OR "cue exposure" OR "cue-reactivity" OR "conditioned response" OR "stimuli") AND ("substance" OR "substances" OR "alcohol" OR "drug" OR "drugs" OR "cocaine" OR "cannabis" OR "marijuana" OR "opioids" OR "opiates" OR "tobacco" OR "nicotine") AND ("craving" OR "urge"). There were no search restrictions based on year of publication or language.1
