Dissertation (MMED Internal Medicine)Viral hepatitis especially hepatitis B (HBV) and hepatitis C(HCV) infections are quite common among opioid drug users. Chronic HBV and HCV may result in decompensated liver cirrhosis and hepatocellular carcinoma. Harm reduction and treatment of chronic HBV and HCV can reduce morbidity and mortality whereas elevated serum alanine aminotransferase (ALAT) may predict HBV and HCV infections among adults with opioid use disorders. To determine the seroprevalence and factors associated with HBV and HCV infections and their relationship to serum ALAT among the adults with opioid use disorders in Dodoma, Tanzania. A cross-sectional study design was conducted from December 2020 to January 2021in which convenience sampling technique was used to recruit the opioid use disorders placed on MST at Itega methadone assisted therapy clinic center. Binary logistic regression was used to find the factors associated with HBsAg and HCV antibodies (anti-HCV) in relation to serum ALAT levels. Out of 254 participants, majority were males 235 (92.5%), unmarried 177 (69.7%), living in urban 251 (98.8%) and self-employed 219 (86.2%) where the mean age was 34.8±7.3 years. Seroprevalence of HBsAg and anti-HCV among the participants were 9.8%and 25.2% respectively. HIV infection was independent associated with positive HBsAg (AOR = 9.91, p-value = <0.0001).The odds of serologic evidence of anti-HCV were higher among the participants who used heroin through injection (AOR= 6.71, p-value = 0.0002), inconsistence condom use(AOR = 3.35, p-value = 0.034), multiple sexual partners (AOR = 10.56, p-value = 0.0003)and methadone dose for more than 120mg (AOR = 5.01, p-value = 0.0003) and criminal justice involvement (AOR = 7.69, p-value = 0.014).Elevated serum ALAT was predicted by serologic evidence of HBsAg (AOR = 7.47, p-value =0.017) and anti-HCV (OR = 4.93, p-value = <0.0001). Among people who use the drug, HCV is still higher while HBV tends to increase. Through harm reduction prevalence of HBV and HCV may be reduced.