Table 2 Results extracted for each research question

Thomson 2012 [21]

Febfast registrants: more likely to be females, be aged between 25 and 54, reside in Victoria, have a higher household income, be working, have completed university (p < 0.001), have been born in Australia, be living in a nuclear family or share house (p < 0.001), agree that alcohol is a serious issue for the community (p < 0.001), classify themselves on the heavier spectrum of drinking style (p < 0.001). Less likely to refuse alcohol when offered to them (p < 0.001), believe that there were benefits (p < 0.001) associated with drinking alcohol. 75.9% of the participants participating for the first time in 2011, those aged 45–54 and 55 + more likely to have participated more than once (p < 0.01). Specific motivations: registrants wanting to “give their body a break” more likely to be aged 25–44 (p < 0.05), have a higher income (p < 0.05), have completed febfast more than once (p < 0.05), be heavier drinkers (p < 0.001). Respondents motivated by “getting out of drinking habits” more likely to have a higher income (p < 0.05), be aged 35–54 (p < 0.05), classify themselves as heavier drinkers (p < 0.01). Motivation to participate to lose weight or to improve health more likely associated with being a heavier drinker (p < 0.001). 81.1% reported knowing at least one person who had also participated (p < 0.001)

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Heavier drinkers more likely not to complete the event (p < 0.01)

25% reporting giving up alcohol for a month was difficult or very difficult. Younger participants more likely to find the experience difficult compared to those aged 45 or older, as those with heavier drinking patterns (p < 0.001).46.5% reporting reduced amount of tobacco products consumed during febfast. 14.7% having learnt new information through febfast (health risk associated with alcohol for 32.0%). 85% of the participants reporting at least one benefit. Most commonly reported benefits: saving money (52.2%), improved sleep (40.5%), weight loss (38.1%), improved overall health (35.3%)

Febfast registrants participating the survey: more likely to be females (74.5% vs. 62.0% of the 2011 participants), to have participated more than once

Febfast respondents: 92.7% inclined to recommend the event to others. 68.4% intending to participate to febfast 2012. 25% purchased at least one Time Out Certificate. Females, participants aged 25–44, those without previous participation to febfast (p < 0.05), heavier drinkers (p < 0.01) more likely to purchase certificates. 45.2% having knowledge of ‘unofficial participants’ doing febfast. Among those having reduced their consumption during febfast, 68.8% reporting maintaining the change after February (21.2% planning to maintain reduced consumption because of health)

Reduced frequency of alcohol consumed following febfast: associated with having a higher income and lighter current drinking patterns (p < 0.05), having experienced benefits while completing febfast (p < 0.001), with each individual benefit significantly associated with a reduced frequency (p < 0.01), except being motivated to save money. Those motivated by the desire to break their drinking habits, to give their body a break from alcohol, improve health, save money, lose weight, or for the personal challenge more likely to reduce frequency of consumption (p < 0.05)

Reduced amount of alcohol consumed following febfast: associated with having experienced benefits while completing febfast (p < 0.001), being motivated to break drinking habits, give the body a break, improve health, lose weight, or seeing febfast as a personal challenge. Motivation to participate with others associated with a decreased likelihood of reducing the amount consumed (p < 0.01)

Australian drinkers’ sample: Less than 30% somewhat or very likely to participate to febfast in the future

de Visser et al. 2016 [20]

64.1% of successful respondents

One independent predictor of success: lower frequency of drunkenness at baseline OR = 0.93, 95%CI [0.90; 0.96]. Correlates of success (at baseline): fewer drinks per drinking days (3.78 vs. 4.21, d* = 0.21, p = 0.01), lower frequency of drunkenness the month before (2.55 vs. 3.84, d = 0.36, p < 0.01), lower AUDIT-score (11.09 vs. 12.56, d = 0.26, p < 0.01), Greater social (3.61 vs. 3.23, d = 0.23, p < 0.01) and emotional (4.35 vs. 4.05, d = 0.16, p = 0.02) DRSE scores

Risk of rebound effect: 11% of reported increased frequency of drunkenness at 6-month follow-up. Unsuccessful participants more likely to report an increase in frequency of drunkenness at 6-month follow-up (p < 0.01, d = 0.39). Successful participants: Increase in all 3 dimensions of the DRSE score at 1-month follow-up (social p < 0.01, d = 0.39, emotional p < 0.01, d = 0.30, opportunistic p < 0.01, d = 0.23). Reduction in alcohol intake at 6-month follow-up (drinking days per week p < 0.01, d = 0.53, drinks per drinking day p < 0.01, d = 0.25, drunk episodes last month p < 0.01, d = 0.39). Unsuccessful participants: increase in DRSE social (d = 0.11, p = 0.03), DRSE emotional (d = 0.23, p < 0.01) at 1-month follow-up, reduction in drinking days per week (d = 0.45, p < 0.01), drinks per typical drinking day (d = 0.18, p < 0.01) and frequency of drunkenness at 6-month follow-up (d = 0.39, p < 0.01)

People who completed all three questionnaires: older, more likely to have completed a dry month in the past, fewer drinks per drinking day, less frequent drunkenness, lower AUDIT score, and greater social DRSE. Successful participants: Similar proportion of males and females (female 62.9%, male 66.7%, p = 0.29)

de Visser et al. 2017 [17]

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62% of successful registrants

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Registrants: at 6-month follow-up lower AUDIT scores (p < 0.01), elevated DRSE scores (social DRSE p < 0.01, emotional DRSE p < 0.01, opportunistic p < 0.01) compared to the unofficial participants

15-fold increase in participation between 2013 (4,000) and 2016 (60,000). Unofficial participants: 7% tried not to drink in January in 2015, and 11% in 2016. Adult drinkers: 64% aware of Dry January in 2015 and 78% in 2016. Successful participants: 96% reported signing up to receive official supportive emails, 69% read every message sent, 71% considered the messages helped them succeed. Successful and unsuccessful participants: 57% chose to receive supportive messages, 78% considered that helped them, 42% used social media support and 73% considered such support helped them

de Visser and Nicholls 2020 [18]

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61% of successful respondents

Four independent predictors of success: being male rather than female (OR = 1.46, 95%CI [1.35; 1.58]), having a lower AUDIT score (OR = 0.97, 95%CI [0.96; 0.98]) or a greater emotional DRSE score at baseline (OR = 1.09, 95%CI [1.06; 1.11]), reading supportive emails ‘always’ rather than ‘never’ (OR = 1.81, 95%CI [1.65; 1.97]). Correlates of successful completion of Dry January: being a male (66.4% vs. 59.2% for females, V = 0.05, p < 0.01), lower AUDIT score (d = 0.24, p < 0.01), lower frequency of drunkenness (d = 0.19, p < 0.01), higher DRSE social (d = 0.21, p < 0.01), emotional (d = 0.23, p < 0.01) and opportunistic (d = 0.18, p < 0.01) scores, higher GSE score (d = 0.10, p < 0.01), higher WEMWBS score (d = 0.12, p < 0.01), higher frequency of reading support emails (V = 0.08, p < 0.01)

All Participants: increased WEMWBS scores (d = 0.34, p < 0.01) and the GSE scores (d = 0.12, p < 0.01) at 1-month follow-up, savings (63%), improved sleep (56%), increased energy (52%), greater health (50%), weight loss (38%). Positive effects of Dry January on savings, sleep, energy, health and weight loss found more frequently in the successful participants' group (savings d = 0.13, p < 0.01; sleep d = 0.15, p < 0.01; energy d = 0.14, p < 0.01; health d = 0.12, p < 0.01; weight d = 0.24, p < 0.01) Successful participants: Increase in GSE score (d = 0.12, p < 0.01) at 1-month follow-up. Unsuccessful participants: no significant change in GSE scores

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de Visser and Piper 2020 [19]

Participants: more likely to be female (75.3% vs. 50.9%, p < 0.01), younger (45.41 vs. 49.82, p < 0.01), higher mean income (p < 0.01), more likely to have completed university education (48.1% vs. 37.7%, p < 0.01), better self-rated physical health (3.23 vs. 2.93, p < 0.01), lower WEMWBS scores (3.37 vs. 3.46, p < 0.01), more concern about the health effects of drinking (6.60 vs. 4.47, p < 0.01) and about control over the drinking (5.53 vs. 3.72, p < 0.01), higher AUDIT-C scores (8.47 vs. 5.74, p < 0.01), lower DRSE (4.30 vs. 5.28, p < 0.01). Significantly more likely to have tried to engage in more physical activity (48.7% vs. 23.8%, p < 0.01) or to improve their diet (52.3% vs. 28.2%, p < 0.01)

62.4% of successful respondents

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Successful participants: increase in self-rated physical-health (baseline mean = 3.26, 95%CI [3.17; 3.35], 1-month follow-up mean = 3.47, 95%CI [3.39; 3.46], 6-month follow-up mean = 3.47, 95%CI [3.39; 3.56]), DRSE scores (baseline mean = 4.27, 95%CI [4.14; 4.40], 1-month follow-up mean = 4.86, 95%CI [4.73; 4.98], 6-month follow-up mean = 4.83, 95%CI [4.69; 4.96]), WEMWBS scores (baseline mean = 3.40, 95%CI [3.34; 3.47], 1-month follow-up mean = 3.77, 95%CI [3.71; 3.83], 6-month follow-up mean = 3.68, 95%CI [3.62; 3.74]), decrease in AUDIT-C scores (baseline mean = 8.89, 95%CI [8.65; 9.12], 6-month follow-up mean = 6.72, 95%CI [6.37; 7.07]). Unsuccessful participants: increase in self-rated physical-health (baseline mean = 3.12, 95%CI [3.01; 3.24], 1-month follow-up mean = 3.20, 95%CI [3.07; 3.32]), 6-month follow-up mean = 3.16, 95%CI [3.04; 3.28]), DRSE scores (baseline mean = 4.63, 95%CI [4.45; 4.82], 1-month follow-up mean = 5.04, 95%CI [4.88; 5.21], 6-month follow-up mean = 4.94, 95%CI [4.76; 5.12]), WEMWBS scores (baseline mean = 3.37, 95%CI [3.28; 3.47], 1-month follow-up mean = 3.56, 95%CI [3.48; 3.66], 6-month follow-up mean = 3.49, 95%CI [3.39; 3.58]), decrease in AUDIT-C scores (baseline mean = 6.82, 95%CI [6.37; 7.27], 6-month follow-up mean = 6.18, 95%CI [5.76; 6.59])

Official registrants: more likely to complete the challenge (69.8% vs. 30.2%, p < 0.01)

Unofficial participants: 30.2% Dry January completion (p < 0.01)

Case et al. 2021 [22]

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(1) Percentage of adults reporting drinking monthly or less frequently: lower in January than non-January months both in 2014/2015 (46% vs. 49%) and 2017/2018 (45% vs. 51%),

(2) Mean weekly alcohol consumption among drinkers: no significant differences between January and non-January months (β** = 0.23, 95%CI [− 0.11;0.58])

(3) Percentage of at-risk drinkers reporting a current attempt to restrict alcohol consumption: higher in January than non-January months in both 2014/15 (25% vs. 20%) and 2017/18 (27% vs. 19%). Odds of at-risk drinkers reporting current attempt to restrict consumption significantly higher in January vs. non-January (OR = 1.46, 95%CI [1.25;1.70])

(4) Percentage of at-risk drinkers citing Detox/Dry January as a motive in their most recent attempt to restrict alcohol consumption: higher in January than non-January months in both 2014/15 (13% vs. 4%) and 2017/18 (18% vs. 11%). Odds of at-risk drinkers citing Dry January as a motive in their most recent attempt to restrict consumption significantly higher in January vs. non-January (OR = 2.29, 95%CI [1.62;3.22]) (5) Percentage of at-risk drinkers reporting use of a website or app to help restrict alcohol consumption in their most recent attempt: No significant differences in January vs. non-January (OR = 0.77, 95%CI [0.33;1.78]), same percentage in January vs. non- January months in 2014/15 (2%) and similar in January vs. non-January in 2017/18 (2% vs. 3%)

(1) Percentage of adults reporting drinking monthly or less frequently: Odds of reporting drinking monthly or less frequently significantly higher in 2017/2018 vs. 2014/2015 (OR = 1.06, 95%CI [1.02;1.10]). Odds of reporting drinking monthly or less frequently in January vs. non-January months not significantly different between 2017/18 and 2014/15. Differences between January and other months similar in 2014/15 and 2017/18 for adults reporting drinking monthly or less frequently and mean consumption among drinkers (OR = 0.91, 95%CI [0.79;1.05], BF*** = 0.05; β = 0.55, 95%CI [− 0.14;1.25], BF = 0.13 , respectively)

(2) Mean weekly alcohol consumption among drinkers: No significant differences between 2017/18 and 2014/15 (β = − 0.003, 95%CI [− 0.20;0.20])

(3) Percentage of at-risk drinkers reporting a current attempt to restrict alcohol consumption: No significant difference between 2017/18 and 2014/15 (OR = 0.92, 95%CI [0.84;1.02]

(4) Percentage of at-risk drinkers citing Detox/Dry January as a motive in their most recent attempt to restrict alcohol consumption: Odds of citing Dry January significantly higher in January vs. non-January in 2014/15 (OR = 3.86, 95%CI [2.15;6.92]) vs. 2017/18 (OR = 1.81, 95%CI [1.18;2.79]). Odds of risky drinkers citing Dry January as a motive in their most recent attempt to restrict alcohol consumption significantly higher in 2017/18 vs. 2014/15 (OR = 2.59, 95%CI [1.90;3.53])

(5) Percentage of at-risk drinkers reporting use of a website or app to help to restrict alcohol consumption in their most recent attempt: No significant differences between 2017/18 and 2014/15 (OR = 1.57, 95%CI [0.94;2.61]). Respondents: Mean weekly consumption ranged from 5.2 units (SD: 8.8) (January 2015) to 5.7 units (SD: 10.3) (January 2018). Of the total sample, 26% were at-risk drinkers (scoring ≥ 5 on AUDIT-C)

Dry July Annual Reports [23,24,25,26,27,28,29]

2009/2010, 2010/2011, 2011/2012, 2012/2013, 2013/2014, 2019, 2020

2009/2010: 43% males, 57% females, 12.9% aged 18–25 years old, 38.5% aged 25–35 years old, 25.0% aged 35–45 years old, 15.2% aged 45–55 years old, 6.0% aged 55 years old or more. 2010/2011: 46% males, 54% females, 15.3% aged 18–25 years old, 34.0% aged 25–35 years old, 23.9% aged 35–45 years old, 17.0% aged 45–55 years old, 9.8% aged 55 years old or more. 2011/2012: 43% males, 57% females, 2012/2013: 43% males, 57% females. 2013/2014: 43% males, 57% females, 14% aged 18–24 years old, 38% aged 25–34 years old, 24% aged 35–44 years old, 14% aged 45–54 years old, 10% aged 55 years old or more. Motivations reported for taking part in the challenge: 59% due to friends or family being affected by cancer, 45% to see if able to complete the challenge, 44% to support their local hospital

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2012 Participants: 76% willing to drink less having completed Dry January, 42% having changed their drinking habits post-Dry July. Mid-year health check: 36% having changed their diet, 36% having increased their current exercise program, 33% going to the gym as an alternative to drinking, 34% visiting their family/friends just because of not drinking. 2013 Participants: 74% willing to drink less having completed Dry January, 44% having changed their drinking habits post-Dry July. Mid-year health check: 22% having changed their diet, 22% having increased their current exercise program, 20% going to the gym as an alternative to drinking 2019 Participants: 21% feeling healthier. 2020: 98% reporting a positive experience

2010/2011: 99% reporting Dry July to be a positive experience, 98% planning to participate again. 2011/2012: 99% reporting Dry July to be a positive experience, 53% reporting that the most rewarding part was sense of achievement, 97% intending to recommend Dry July to friends, family and work colleagues. 2012/2013: 99% reporting Dry July to be a positive experience, 36% reporting that the most rewarding part was sense of achievement, 73% intending to participate to Dry July 2014, 96% intending to recommend Dry July to friends, family and work colleagues. 2019: 42% reporting sense of achievement 2020: 75% intending to do dry again to support the cause, 45% reporting the sense of achievement to be the most rewarding