Smoking behavior characteristics of non-selected smokers with childhood attention-deficit/hyperactivity disorder (AD/HD) history: a systematic review and meta-analysis.

It is unclear whether adult smokers with childhood attention-deficit/hyperactivity disorder history (CH) have more severe smoking behavior than non-CH smokers, while it is clearly suggested that CH adolescents have more severe smoking behavior than CH adolescents. The aim of the present comprehensive meta-analysis is to determine whether CH smokers have more severe smoking behavior characteristics than those without and the effect of age on the association between CH and smoking behavior. We included all case-control studies and first round data collection of observational studies addressing the difference in smoking behavior characteristics of CH smokers versus non-CH smokers, with validated scales or structured interviews, without any language or date restriction. Nine studies (including 365 smokers with CH and 1,708 smokers without) were included. Compared to non-CH smokers, CH smokers smoked significantly more cigarettes [standardized mean differences (SMD) = 0.15, 95 % CI 0.01-0.28, p = 0.04] and began to regularly smoke earlier (SMD = -0.28, 95 % CI -0.49; -0.07, p = 0.01) but were not significantly more nicotine dependent (SMD = 0.23, 95 % CI -0.04 to 0.48, p = 0.08). After removing the single adolescent study, the significant association between CH and number of daily smoked cigarettes disappeared, and subgroups analyses confirmed that the significant association between CH and number of daily smoked cigarettes disappeared as age increased. Our meta-analysis illustrates a clinically important link between CH and tobacco smoking in adolescence but not later in life. Further high-quality studies are needed to confirm this finding, as only two studies included participants with a mean age below 20 years.