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PrEP stands for pre-exposure prophylaxis. PrEP is a highly effective HIV prevention strategy that HIV-negative people can use to lower their chance of getting HIV. Use of PrEP involves taking antiretroviral (anti-HIV) drugs and having regular medical appointments for monitoring and support.

The PrEP cascade describes the stages of engagement with PrEP as an HIV prevention strategy. It is similar to the HIV care cascade, which describes the stages of engagement in HIV care from testing and diagnosis to successful treatment outcomes. The stages of the PrEP cascade vary but generally move from an awareness of PrEP for HIV prevention to deciding to use PrEP, accessing PrEP and starting and being adherent to a PrEP regimen.1,2,3,4,5 Examining engagement along the PrEP cascade can help us understand barriers to PrEP use, including health system barriers such as lack of knowledge among healthcare providers, and develop programs and services to overcome these barriers.

This article summarizes a systematic review that used key variables from the PrEP cascade to examine PrEP use among people who inject drugs.6

PrEP and people who inject drugs

PrEP can be used by people who inject drugs to help prevent the transmission of HIV through injection drug use, in addition to helping to prevent the sexual transmission of HIV.7,8,9

PrEP is just one of the approaches to prevent HIV transmission among people who inject drugs: it should be used alongside community-based harm reduction approaches such as needle and syringe distribution programs and safer consumptions sites.

What kind of research does the systematic review include? 

The systematic review looked at PrEP use among people who inject drugs by examining six variables that reflect different stages along the PrEP cascade:

  1. Awareness of PrEP as an HIV prevention strategy
  2. Knowledge of PrEP
  3. Perception of one’s own risk for HIV
  4. Willingness to use PrEP for HIV prevention
  5. Access to HIV healthcare providers
  6. Starting and adhering to PrEP

Twenty-three articles were included in the review. A study was included if it presented quantitative or qualitative findings on one or more of the six variables and included results for people who inject drugs in the United States. All of the studies were published between 2013 and 2020. Most of them involved participants who had reported injecting drugs within the past six months and were currently on methadone.

What is the engagement of people who inject drugs with PrEP?

Awareness of PrEP as an HIV prevention strategy

Being aware of PrEP as a way to prevent HIV transmission is an important first step in engaging with the PrEP cascade. Nineteen studies examined PrEP awareness among people who inject drugs. PrEP awareness among participants in these studies ranged from 1% to 57%.

Knowledge of PrEP

Knowledge of PrEP includes knowing specific information about PrEP such as the effectiveness of PrEP at preventing HIV transmission and how PrEP is taken. Five studies examined PrEP knowledge among people who inject drugs. Less than 40% of participants in these studies reported PrEP knowledge.

Perception of one’s own risk for HIV

The use of PrEP and other HIV prevention strategies is affected by a person’s self-perceived risk for HIV. Five studies examined the HIV risk perception of people who inject drugs. In these studies, 1.1% to 66% of participants perceived themselves to be at risk for HIV.

Willingness to use PrEP for HIV prevention

The authors of the review used PrEP acceptability and intent to use PrEP as indicators of willingness to use PrEP. Fourteen studies examined participants’ willingness to use PrEP using qualitative analyses. These studies found that a range of characteristics were associated with an increased willingness to use PrEP among people who inject drugs, but the review did not draw generalizations from these findings as each study found different results. The characteristics included having a high perception of risk for HIV, having support services (e.g., social support, support from healthcare providers), being female, experiencing homelessness and being less than 50 years old.

Access to HIV healthcare providers

Eleven studies examined participants’ access to HIV-related services. In nine of these studies, community-based organizations, needle and syringe distribution programs and addiction treatment services were the primary places where participants accessed HIV prevention services (i.e., where PrEP services could be available). Only one study looked at where people were accessing PrEP. This study found that 55% of people on PrEP and methadone maintenance were prescribed PrEP in the addiction treatment setting, with an additional 14% reporting they got it from a mobile health van.

In a single study, among people aware of PrEP, only 18.4% of people who inject drugs had discussed PrEP with a healthcare provider.

Finally, 86% of the participants in the single study that examined preference for HIV testing reported that they would rather access HIV testing in a needle and syringe distribution programs than in a sexually transmitted infection (STI) program.

Starting and adhering to PrEP

Ten studies examined PrEP use among people who inject drugs. PrEP use was low in these studies, ranging from no participants on PrEP to 3% of participants on PrEP.

Adherence is key to the effectiveness of PrEP, but no studies that measured PrEP adherence in this population were included in the review.

What are the implications of the review for service providers? 

This systematic review demonstrates that more work is needed to engage people who inject drugs with PrEP, including increasing their awareness of PrEP, PrEP knowledge, willingness to use PrEP, access to PrEP and PrEP use and adherence. Research shows that there is a willingness to use PrEP among people who inject drugs but that overall PrEP use is low.

Service providers have a role to play in increasing the uptake of PrEP among people who inject drugs. This includes increasing awareness and understanding of PrEP in the community and linking people who inject drugs to PrEP providers. Provision of PrEP services may best be done in locations where people who inject drugs are already accessing HIV prevention services, such as community health centres and needle and syringe distribution programs.

When considering PrEP use among people who inject drugs, it is also important to be aware of additional factors that affect PrEP engagement.

  • There are many barriers to PrEP for people who inject drugs. There is a need to address individual-level barriers to PrEP use among people who inject drugs, including homelessness, access to healthcare professionals and stigma related to drug use and HIV.
  • While the review focused on many individual-level variables affecting engagement in PrEP care, variables at the service provider level also influence the use of PrEP by people who inject drugs. These include service providers’ knowledge and ability to provide PrEP care as well as the accessibility of the services they are delivering.10,11 To better engage people who inject drugs in PrEP care, service providers should identify the gaps in their own knowledge and work with people who inject drugs to understand and address the barriers that may exist to PrEP services.
  • PrEP should be considered within the context of existing strategies to prevent HIV transmission during drug use and the prevention preferences of people who inject drugs. Concerns with PrEP voiced by people who inject drugs include the use of resources for PrEP where access to other effective harm reduction strategies like safer injecting supplies is limited and underfunded.12
  • PrEP does not prevent other harms associated with injection drug use like the transmission of hepatitis C or other harms associated with sex like STIs. The use of a combination of prevention strategies continues to be important for addressing these concerns.

When considering this review, it is important to remember that:

  • The review primarily focused on the earlier stages of the PrEP cascade, with five of the six variables relating to a person’s decision to start PrEP and their ability to access it. Only the last variable examined starting and adhering to PrEP, with only one study addressing PrEP adherence. Further research is needed to better understand retention in care, adherence and ongoing use of PrEP among people who inject drugs.
  • This review focused on people who inject drugs in the United States, with most studies being conducted in urban areas. The results may not reflect people who inject drugs in Canada or people who inject drugs in rural settings.

What is a systematic review?

Systematic reviews are important tools for informing evidence-based programming. A systematic review is a critical summary of the available evidence on a specific topic. It uses a rigorous process to identify all the studies related to a specific research question. Relevant studies can then be assessed for quality and their results summarized to identify and present key findings and limitations. If studies within a systematic review contain numerical data, these data can be combined in strategic ways to calculate summary (“pooled”) estimates. Combining data to produce pooled estimates can provide a better overall picture of the topic being studied. The process of pooling estimates from different studies is referred to as a meta-analysis.


  1. Holt M, Lee E, Lea T et al. HIV preexposure prophylaxis cascades to assess implementation in Australia: results from repeated, national behavioral surveillance of gay and bisexual men, 2014-2018. Journal of Acquired Immune Deficiency Syndromes. 2020 Mar 1;83(3):e16-22.
  2. Newman PA, Guta A, Lacombe‐Duncan A et al. Clinical exigencies, psychosocial realities: negotiating HIV pre‐exposure prophylaxis beyond the cascade among gay, bisexual and other men who have sex with men in Canada. Journal of the International AIDS Society. 2018 Nov 18;21(11):e25211. Available from: https://onlinelibrary.wiley.com/doi/10.1002/jia2.25211
  3. Parsons, JT, Rendina HJ, Lassiter JM et al. Uptake of HIV pre-exposure prophylaxis (PrEP) in a national cohort of gay and bisexual men in the United States: the motivational PrEP cascade. Journal of Acquired Immune Deficiency Syndromes. 2017 Mar 1;74(3):285-92. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315535/
  4. Nunn, AS, Brinkley-Rubinstein L, Oldenburg CE et al. Defining the HIV pre-exposure prophylaxis care continuum. AIDS. 2017 Mar 13;31(5):731-34. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5333727/
  5. Brouwers P. Improving the HIV pre- exposure prophylaxis (PrEP) cascade. Bethesda (MD): National Institute of Mental Health; 2015. Available from: https://www.nimh.nih.gov/funding/grant-writing-and-application-process/concept-clearances/2015/improving-the-hiv-pre-exposure-prophylaxis-prep-cascade
  6. Mistler CB, Copenhaver MM, Shrestha R. The pre-exposure prophylaxis (PrEP) care cascade in people who inject drugs: a systematic review. AIDS and Behavior. 2021 May; 25(5):1490-1506.
  7. Tan DHS, Hull MW, Yoong D et al. Canadian guideline on HIV pre-exposure prophylaxis and nonoccupational postexposure prophylaxis. Canadian Medical Association Journal. 2017 Nov 27;189(47):E1448-58. Available from: http://www.cmaj.ca/content/189/47/E1448
  8. Choopanya K, Martin M, Suntharasamai P et al. Antiretroviral prophylaxis for HIV infection in injecting drug users in Bangkok, Thailand (the Bangkok Tenofovir Study): a randomised, double-blind, placebo-controlled phase 3 trial. Lancet. 2013;381:2083-90.
  9. Martin M, Vanichseni S, Suntharasamai P et al. The impact of adherence to preexposure prophylaxis on the risk of HIV infection among people who inject drugs. AIDS. 2015 Apr 24;29(7):819-24.
  10. Zhang C, McMahon J, Fiscella K et al. HIV pre-exposure prophylaxis implementation cascade among health care professionals in the United States: implications from a systematic review and meta-analysis. AIDS Patient Care and STDs. 2019 Dec;33(12):507-527. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6918849/pdf/apc.2019.0119.pdf
  11. Hershow RB, Gonzalez M, Costenbader E et al. Medical providers and harm reduction views on pre-exposure prophylaxis for HIV prevention among people who inject drugs. AIDS Patient Care and STDs. 2019 Aug;31(4):363-379. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7289066
  12. International Network of People who Use Drugs. Pre-exposure prophylaxis (PrEP) for people who inject drugs: community voices on pros, cons and concerns. London (UK): International Network of People who Use Drugs; 2016. Available from: https://www.inpud.net/sites/default/files/INPUD%20PrEP%20-%20Community%20Voices%287%29.pdf



About the author(s)

Erica Lee is CATIE’s manager, website content and evaluation. Since earning her Master of Information Studies, Erica has worked in the health library field, supporting the information needs of frontline service providers and service users. Before joining CATIE, Erica worked as the Librarian at the AIDS Committee of Toronto (ACT).