Fig. 4
![Fig. 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs43094-021-00245-z/MediaObjects/43094_2021_245_Fig4_HTML.png)
Mann–Whitney U statistics, frequency distribution for 6-MAM concentration in random heroin addicts’ group and addicts going through rehabilitation at the de-addiction center group. There is a significant difference between mean rank for addicts undergoing rehabilitation compared to random regular addicts for 6-MAM levels in the hair sample