MMT	methadone maintenance treatment.
PCR	polymerase chain reaction.
OTUs	operational taxonomic units.
RDP	ribosomal database project.
ANOVA	analysis of variance.
ACE	abundance-based coverage estimator.
PCoA	principal coordinate analysis.
PCA	principal component analysis.
PERMANOVA	permutational multivariate analysis of variance.
LDA	linear discriminant analysis.
LEfSe	linear discriminant analysis effect size.
BMI	body mass index.
CD	compulsory detention (participants).
MP	MMT patients.
DU	drug users.
HC	healthy controls.