BackgroundSubstance use is disproportionately high among people who are homeless or vulnerably housed. We performed a systematic overview of reviews examining the effects of selected harm reduction and pharmacological interventions on the health and social well-being of people who use substances, with a focus on homeless populations. Methods and findingsWe searched MEDLINE, EMBASE, PsycINFO, Joanna Briggs Institute EBP, Cochrane Database of Systematic Reviews and DARE for systematic reviews from inception to August 2019. We conducted a grey literature search and hand searched reference lists. We selected reviews that synthesized evidence on supervised consumption facilities, managed alcohol programs and pharmacological interventions for opioid use disorders. We abstracted data specific to homeless or vulnerably housed populations. We assessed certainty of the evidence using the GRADE approach.

annabis use by pregnant and lactating people is increasing, though it is difficult to establish the prevalence of cannabis use in pregnancy. Reported prevalence varies from 2% to 36%, depending on the methodology used to detect use, the population studied and the definition of use. [1][2][3][4][5][6][7][8][9][10][11][12] Pregnant people have reported using cannabis to manage pregnancy-related conditions (e.g., nausea, weight gain, sleep difficulty) [13][14][15][16][17][18][19] and pre-existing conditions (e.g., mental health, insomnia, chronic pain), 13,14,18 as well as to improve mood, mental, physical and spiritual well-being, 16,18 provide pleasure and manage stress. [13][14][15][16] Recent systematic reviews have not found empirical data on reasons for cannabis use during lactation. 20,21 Evidence is still emerging about clinical outcomes related to cannabis use during pregnancy and lactation, and wellcontrolled studies are lacking. [22][23][24] The available evidence is limited by reliance on self-reported data about dose, composition and timing of exposure, the changing nature of tetrahydrocannabinol levels in cannabis over time, and a lack of studies that control for known confounders such as polysubstance and tobacco use. [25][26][27][28][29][30][31] The available evidence does suggest that cannabis use during pregnancy may be associated with complications such as low birth weight, childhood neurodevelopmental outcomes and preterm birth. [22][23][24]32,33 Very few studies have analyzed the outcomes associated with cannabis exposure through breastmilk, with 1 study suggesting decreased infant motor development and another showing no effects on developmental outcomes. [34][35][36] Given the potential harms identified, and in the absence of high-quality evidence available to guide practice, most clinical guidelines recommend abstinence from cannabis during pregnancy and lactation. [37][38][39] People who perceive benefits from cannabis may wish to or may be motivated to continue using it through pregnancy and lactation, however. Counselling that explores the reasons