Main findings for use or intention to use illicit drugs
| Pooling | Outcome | Design | References | Subgroups | Number of subjects exp vs ctrl† | Effect measure | Effect size (95% CI) or effect direction (p-value)‡ | Heterogeneity p-value¶ |
|---|---|---|---|---|---|---|---|---|
| Pooled analyses | Use of illicit drugs | RCT | Slater et al 2006;10 Fang et al 2010;18 Newton et al 2010;11 Schwinn et al 2010;19 Lee et al 201028 | – | 2701 vs 2769 | SMD, random effects | −0.02 (−0.15 to 0.12) | 0.020* |
| Intention to use illicit drugs | RCT | Polansky et al 1999;25 Yzer et al 2003;26 Zhao et al 2006;27 Fang et al 201018 | – | 771 vs 499 | SMD, fixed effects | −0.07 (−0.19 to 0.04) | 0.840 | |
| Past-month use of methamphetamine | 4 ITS and 1 CBA | Meth Project studies12–16 | age 12–17 | 14 865 vs 7497 | OR, random effects | 1.16 (0.83 to 1.61) | – | |
| age 18–24 | 347 vs 632 | OR, random effects | 1.63 (0.70 to 3.79) | – | ||||
| Past-year use of methamphetamine | 4 ITS and 1 CBA | Meth Project studies12–16 | age 12–17 | 17 105 vs 7497 | OR, random effects | 0.59 (0.43 to 0.81)** | – | |
| age 18–24 | 1039 vs 632 | OR, random effects | 0.70 (0.34 to 1.45) | – | ||||
| Single studies | Lifetime, past 90-day, or past-30-day use of marijuana | RCT (community-media) | Slater et al 201121 | – | NA (3236) | OR, random effects | 0.60 (0.38 to 0.94)* | – |
| Cohort (mass-media) | – | OR, random effects | 0.26 (0.19 to 0.35)*** | – | ||||
| Past-year use of marijuana | Cohort | Hornik 200622 | – | NA (3529) | OR, fixed effects | 1.21 (1.19 to 1.65)* | – | |
| Intention to use marijuana | – | NA (2915) | OR, fixed effects | 0.89 (0.79 to 1.00)§ | – | |||
| Past 12-month episodes of cannabis intoxication | Cohort | Scheier and Grenard et al 201023 | age 13–14 | NA (2515) | mean difference, SEM | −0.022 | – | |
| age 15–18 | mean difference, SEM | 0.144* | – | |||||
| Past 30-day use of marijuana among high-sensation seekers | ITS | Palmgreen et al 200124 | Fayette | NA (3174) | test for slope | ↓ (p=0.001) | – | |
| Knox, first campaign | NA (3197) | test for slope | ↓ (p=0.001) | |||||
| Knox, second campaign | test for slope | ↓ (p=0.002) | – | |||||
| Past 30-day use of marijuana (girls, 8th grade) | ITS | Carpenter and Pechmann 20112 | – | NA (130 245) | OR, fixed effects | 0.67 (0.52 to 0.87)** | – | |
| Frequency of use of 10 types of drugs | CBA | Miller et al 200020 | – | 567 vs 431 | mean difference, ANOVA | for LSD: ↑ (p<0.001) for marijuana, cocaine, amphetamine, and heroin: ‘no longer significant’ differences | – |
§p<0.10 *p<0.05 **p<0.01 ***p<0.001.
†NA=breakdowns of students exposed to the interventions were not available. Number of analysed subjects is between brackets.
‡Whenever the effect size was not reported, ↓=decreased use or intention to use, and ↑=increased use or intention to use.
¶Heterogeneity test for meta-analyses of RCTs.
ANOVA, analysis of variance; CBA, controlled before and after; Cohort, prospective cohort; ITS, interrupted time-series; RCT, randomised controlled trial; SEM, structural equation modelling; SMD, standardised mean difference.