To tackle the tuberculosis (TB) epidemic, in 2014 the World Health Organization launched the End TB Strategy, which includes action to prevent latent TB infection (LTBI) reactivation. Available preventive treatments (PT) are based on either isoniazid (INH) alone or rifampicin (RIF)-containing regimens. This study aims to assess and compare PT completion rates, the occurrence of adverse events, and the time of dropout among those receiving INH-alone or RIF-containing regimens at Villa Marelli Institute, Milan, Italy, covering the period from 1992 to 2018. A total of 19,670 subjects, belonging to various risk groups—mainly young (median age of 29 years), foreign-born (73.3%), and males (58.8%)—with presumed LTBI were prescribed PT (79.3% INH-alone and 20.7% RIF-containing regimens). The treatment completion rate was 79.4% on average, with higher rates among those receiving RIF-containing regimens (85.6%) compared to those that were prescribed INH-alone (77.8%) (p < 0.0001). Notably, some of the high-risk groups for progression of LTBI were more likely to complete PT from RIF-containing regimens. These groups included recent TB contact (89.9%, p < 0.0001), healthcare workers (93.5%, p < 0.0001), and homeless people (76.6%, p < 0.0001). Irrespectively of the chosen PT regimen, most of the dropouts occurred between the start of the treatment and the first follow-up visit (14.3%, 15.2% for those on INH-alone vs. 11.1% for those on RIF-containing regimens). Further shortening of the PT regimen is therefore an aim to ensure adherence, even though it might need further efforts to enhance the patient’s attitude towards starting and carrying out PT.