Youth-friendly sexual and reproductive health (SRH) interventions are essential for the health of adolescents (10–19 years). Co-designing is a participatory approach to research, allowing for collaboration with academic and non-academic stakeholders in intervention development. Participatory action research (PAR) involves stakeholders throughout the planning, action, observation, and reflection stages of research. Current knowledge indicates that co-producing SRH interventions with adolescents increases a feeling of ownership, setting the scene for intervention adoption in implementation settings.
The period of the maturation and development of adolescents into adulthood is an important phase of one’s life that is often accompanied by heightened sexual attention, thought, and experimentation. The chance of contracting sexually transmitted infections (STIs), unintended pregnancies, or early childbearing increases with ill-informed early sexual experimentation 
. Adolescents across the globe face sexual and reproductive health (SRH) complications, due to a lack of informative services, barriers to such services, social stigmas, laws, and policies 
. The adolescent period involves significant development; thus, it can be determinative of SRH risks in later life. Consequently, adolescence is an optimal stage for targeted SRH interventions [2,3]
. Providing suitable adolescent sexual and reproductive health (ASRH) interventions at the appropriate time and setting makes it possible to improve these statistics in the future.
Co-designing is a participatory action research (PAR) approach that allows community and individual involvement in developing and implementing interventions by providing a personal opinion, expertise, and life experience on the relevant topic 
. This gives the investigator a deeper understanding of the community’s requirements, which might otherwise be misunderstood or misinterpreted [4,5,6,7]
Co-designing has been applied to various fields that require scientific understanding to be balanced with the public’s knowledge, information, and experience. This has resulted in many valuable improvements, as adolescents and academics benefit from knowledge sharing and exchange [3,6]
. Overall, academics view the collaboration with non-academic stakeholders as a rewarding and enriching experience of learning contextual knowledge 
. Co-designing addresses power imbalances in research partnerships, whereby design partners are involved and treated as equals in all decision-making 
. Further, studies that involved co-designing with adolescents indicated that adolescent involvement in the planning, design, and development stages ensured the intervention met the adolescent’s needs and captured their perspectives, insights, and lived experiences, thus providing a better context 
. One review of the effectiveness of initiatives to improve adolescent access to and utilization of SRH services in low and middle income countries (LMICs) found that adolescent involvement in project stages created more than a twofold increase in the self-reported use of SRH services, compared to when such initiatives were not made 
Co-designed health programs and interventions are increasingly being implemented into different settings across the globe to induce health improvements in communities. Consequently, there is a need to understand how these can best be delivered across health systems and diverse settings 
. There is also a need to understand the barriers to co-designing and how these can be overcome 
. ASRH issues and interventions can be subject to limited funding and political challenges, similar to any other health issues, in general, that may limit the scale, scope, and methodologic rigor. In turn, this can limit the reproducibility, generalizability, and dissemination of the research 
. The current understanding of co-designed interventions is that co-producing implementation strategies with non-academic stakeholders enable stakeholder ownership of these implementation strategies, setting the scene for their adoption in implementation settings. However, this has not yet been reviewed systematically 
2. The Benefits of Co-Designing ASRH Interventions
Following the PAR framework, adolescents were engaged in developing SRH interventions through the planning and action stages. During the planning aspects of the interventions, adolescents were involved in preparing and submitting the proposal [13,29]. This information was provided by adolescents’ involvement in youth leadership groups and workshops, which aided the design team in the rapid development of the intervention [13,29].
The information and insight provided by the adolescents allow the primary research to gain an improved understanding of their current knowledge on SRH topics and what they want to gain from the intervention [19,24,38,41]. Throughout the action stages, adolescents were involved in trialing, collecting data, questioning fellow adolescents, and other pilot testing interventions. Adolescent-led, semi-structured, one-on-one interviews, group discussions, and advisory groups were used to explore a range of SRH issues and consult on how best to engage with the broader community for a successful project to address culturally-sensitive issues [13,28,30]. Through the implementation and troubleshooting of the interventions, adolescents were able to supply feedback and improvements to adapt to the intervention [24,25,31,32,33,34,39,40].
3. Different Ways Adolescents can be Involved in PAR
Although the age groups, number of participants, and setting of the studies were identified, there was no difference in the extent to which adolescents were involved between the study characteristics. The only identified difference was that smaller participation groups allowed for slightly more detail in their explanations of their current knowledge on ASRH and what knowledge they wanted to gain [19,24,38,41]. Although these findings indicate that adolescents can be successfully involved in the planning and action stages of the PAR framework, the collective theme of the included studies concluded that with the development of a SRH intervention and a greater understanding of local perspectives, adolescents play a vital role in co-designing ASRH interventions.
4. The Barriers and Facilitators to Co-Designing ASRH Interventions
Barriers stemming from cultural and social influences, judgment, and taboos were highlighted throughout those studies [16,20,23,30,39]. However, the physical barriers, relating to remote communities and poor transport, identified in some studies were directly identified by other studies and used technology to connect and overcome geographical and transportation limitations [18,19,24,33,34,35,40]. An overarching facilitator of the studies was that the research was conducted in a friendly and professional manner, as well as to remind the adolescents that they are in a safe environment at all times [24,28,31,32,36].
Another objective was to assess the effectiveness of co-designing on adolescents’ SRH outcomes. However, as the identified studies did not report on the effectiveness of co-designing ASRH interventions, this objective could not be met.
The collective theme of the included studies concluded that with the development of a SRH intervention, as well as a greater understanding of local perspectives, adolescents play a vital role in co-designing ASRH interventions.
As there is no current systematic review on this topic, it is suggested that the barriers and facilitators, verbalised by the adolescents, be accommodated in future research to improve the effectiveness of the interventions. Future studies should also involve adolescents in these interventions’ observation and reflection aspects, in order to complete the PAR cycle. Furthermore, future systematic reviews should assess the outcomes of these designed interventions documented to assess their effectiveness.