In total, 51,891 people clicked on the social media advert which took them to the study website displaying an information sheet and next steps to express an interest. Five hundred forty people (1% of people reached) continued onto telephone screening by the study team and 221 (0.43% of enrolled vs reached) women enrolled on the study.

In comparison, 2058 women received an invitation pack from their GP practice (N = 32), enclosing the same information as the study website. One hundred eight (5.3%) women contacted the Clinical Trials Unit and were screened for eligibility and 65 (3.16% of enrolled vs reached) women enrolled on the study. Despite the low conversion rate between reached and enrolled from social media, overall, this route of advertisement was active for the shortest period and was accountable for 53.9% of enrolled participants (Table 1).

Table 1 Overall number of people reached, screened, not enrolled and enrolled in each recruitment route

The recruitment data suggests that leveraging multiple recruitment channels, including both traditional healthcare routes and digital/community-based approaches, may help recruit a diverse study population in terms of both acne characteristics and demographic representation (Table 2).

Table 2 Participant characteristics and clinical characteristics by route of recruitment

Women recruited through community and social media advertising had higher acne severity at baseline, with 62.2% (n = 23) and 57.5% (n = 127), respectively, having an investigator global assessment (IGA) score of 3 or more. These proportions were notably higher compared to participants recruited through primary care (46.2%, n = 30) and secondary care (46.0%, n = 40). Furthermore, social media advertising yielded a notably different patient profile regarding disease duration. Among women recruited through this method, 60.2% (n = 133) reported having acne for over 5 years. This represented a larger proportion compared to other strategies: primary care (49.2%, n = 32), secondary care (39.1%, n = 34) and community advertising (40.5%, n = 15).

Regarding participant ethnicity, primary and secondary care attracted slightly more individuals with White backgrounds (92.3% and 81.6%, respectively) than community (72.9%) and social media advertising (76.9%) approaches.

In absolute terms, social media advertising recruited nearly three times as many women from ethnic minority backgrounds (N = 20) compared to the combined primary, secondary and community routes (N = 8).

Notably, no significant differences were observed between the recruitment route and participant age, suggesting the various methods were able to reach a similar age distribution.

Cost implications

From 11 June 2021 to 31 August 2021 (14 months), in-house social media recruitment incurred costs of £6649.30, yielding 209 enrolled participants. This equates to an approximate cost of £31.82 per participant. In contrast, using a mail-out service for participant identification at participant identification centres (PICs) cost £175.26, resulting in 24 enrolled participants at £7.30 per participant.

Retention

Defined by primary outcome data completeness, participant retention rates varied across recruitment routes at both the 12-week and 24-week follow-up points, with some differences in retention by recruitment method. At the 12-week follow-up visit, which was conducted remotely or face to face, retention was highest among participants recruited through social media advertising (85%), followed closely by primary care recruitment (84%). Community advertising yielded a slightly lower retention rate 79%, while secondary care recruitment showed the lowest retention at this stage, with 73% of participants completing the 12-week measure (Table 3).

Table 3 Participant retention by route of recruitment

By the 24-week endpoint, which only involved a remote questionnaire, retention had declined across all routes, though primary care recruitment shows relatively strong retention (75%), followed by community advertising (74%) and social media (72%). Secondary care recruitment again had the lowest retention rate at this stage (68%).

The variability in retention across recruitment routes highlights the importance of varied recruitment routes to balance initial recruitment with sustained engagement throughout the study. The drop-off in retention over time observed across all routes also signifies the importance of implementing effective retention strategies to keep participants engaged through follow-up.

Participant perspectives and experiences of social media advertisement and the sign-up process for the SAFA trial

Twelve SAFA trial participants completed an interview (Table 3).

Targeted advertisements resonated with the audience

Many participants described actively seeking acne-related care online, including through social media platforms. They highlighted the perceived value of the targeted advertisements they saw for the SAFA clinical trial, as the ads were tailored to their specific needs and characteristics, specifically geographic locality, gender, age and condition (Table 4).

Table 4 Characteristics of interview participants

I think it was something along the lines of, ‘Are you between…?’ and then a certain age and, ‘…suffering from adult acne?’ I was like, ‘Yes. Me!’ Katy, age 27.

Receiving information about SAFA through social media was generally seen as an acceptable and welcomed way to be made aware and learn about trials and access to new treatment opportunities that they would otherwise might not have known about.

I wish I knew about more trials going on because you’d be able to participate in those. I was searching for a very specific thing, which is how I got to find this trial. Sam, age 25.

A few participants had repeated exposure (two or three viewings) to the social media advert before clicking on it and submitting an expression of interest. They did not report the repeated exposure as bothersome and instead, this seemed to motivate the reader to engage with the advert.

..it’s come up again. Somebody is saying something here, so maybe I should just try it. Sam, age 25.

Participants who were not recruited through social media also endorsed this strategy, recognising its potential effectiveness for reaching a wide audience quickly.

social media is the fastest way with this group to spread information. It really makes sense to try and capitalise on that. Linda, age 32.

Several participants also mentioned that the advert was forwarded to them, suggesting that showing the advert to a wider audience could also be a snowball sampling strategy to enhance trial recruitment [16].

Building trust through signals of credibility

Participants highlighted the importance of visually appealing and high-quality graphics in the social media advertisements, as these elements were suggested to help capture their attention and contribute to perceptions of legitimacy. Accounts around making judgements about legitimacy were further supported by recognisable NHS and university logos, as well as linking to further information on the SAFA trial website.

the NHS logo on it, quite detailed information about the study, contact information so I could then..find a bit more information about it and verify it’s the real thing. Laura, age 36.

However, some participants expressed a greater degree of scepticism towards social media advertisement than others. A participant who was invited through their GP surgery suggested they would be more likely to trust an invitation that came directly from their healthcare provider.

I would have definitely been cautious about it [social media advert]…I think it would have really heavily depended on the imagery and where it linked in through. Kat, age 30.

This suggests that emphasising the credibility of the source may be particularly important in optimising engagement with a social media advert, as well as the use of links to and from trusted websites outside of social media platforms.

Leveraging existing online communities

Many participants reported being active in international online acne communities, such as Facebook groups and Reddit forums. These spaces offered opportunities to share experiences and learn about various acne treatments. Through their engagement with members from the USA, many participants had already heard of spironolactone, SAFA’s trial intervention, before enrolling but had not been offered it by their GP, despite a few of them directly enquiring about the drug. This familiarity appeared to reduce perceived risks and increase participants’ openness to joining the trial. The exchange of information among people with similar experiences in these communities functioned as a form of organic social proof, building genuine trust and credibility around the trial drug, which may have influenced enrolment decisions. One participant suggested future advertisements could include leveraging the influence of social media figures who could openly discuss their acne journey and share their experience of participating in the trial.

it’s also looking at social media influencers, if there are any social media influencers that actually have quite bad acne themselves, getting them to do the trial. Then they can then obviously talk about their experience on social, and other people might then want to do it. Jasmine, age 22.

Developing relationships with influential voices within acne-focused online communities could be a valuable strategy for raising awareness and driving participation.

Streamlining the onboarding process

Participants recruited through social media advertisements generally experienced a direct and low-effort recruitment process.

I was worried there might be loads of hoops to jump through and it would end up dragging on for so long that I’d give up! But actually it was really quick and easy to get involved. Laura, age 36.

The relatively seamless onboarding process, supported by responsive research staff, appeared to play a crucial role in facilitating a positive transition from initial interest to enrolment in the trial.

Those recruited through other pathways, such as secondary care, were unaware of the trial until they were invited by a member of clinical staff.

I went on to the study was because I went to a dermatologist appointment… I was given an information leaflet to go away with and then the team conducting the study called me and that’s how it all started. Liz, age 36.

After being invited to participate in the study, participants recruited through all pathways reported that responsive research staff provided a positive experience through to enrolment and were important to their choosing to join the trial.