ObjectiveTo observe the changes of 5-hydroxytryptamine (5-HT) level in the plasma, anxiety, and depression of heroin addicts after withdrawal and explore the correlations between 5-HT, anxiety, and depression after withdrawal.Methods A total of 53 heroin addicts were enrolled from a compulsory rehabilitation center and the withdrawal of heroin lasted for 26 weeks. Anxiety and depression symptoms were assessed by self-rating anxiety scale（SAS）and self-rating depression scale (SDS) before and after withdrawal. Plasma 5-HT and 5-hydroxyindoleacetic acid（5-HIAA）levels were detected and the 5-HT turnover rate was calculated. ResultsThe SAS score of heroin addicts significantly decreased after 26 weeks of withdrawal (t=2.196, P<0.05) and the SDS score did not change remarkably (t=1.127, P>0.05). The plasma 5-HT (t=-7.083, P<0.001) and 5-HIAA (t=-4.316, P<0.001) levels of heroin addicts significantly increased, while the 5-HT turnover rate significantly decreased (t=4.026, P<0.001). The plasma 5-HT levels at baseline (r=-0.28, P<0.05) and after 26 weeks of withdrawal (r=-0.295, P<0.05) negatively correlated with SAS scores at baseline and after 26 weeks of withdrawal. The plasma 5-HT level did not correlate with the SDS score (P>0.05).ConclusionThe relief of anxiety of heroin addicts after withdrawal may be relevant to the increase of plasma 5-HT level.