<b><i>Introduction:</i></b> COVID-19 has had a great impact on mental health in the general population. However, few studies have focused on patients with substance use disorders (SUDs). This research aimed to compare the clinical status and substance use patterns of SUD outpatients, before and during confinement due to the COVID-19 pandemic. <b><i>Methods:</i></b> This multicentre study recruited 588 patients (29.2% women; M age = 47.4 ± 11.7 years) in thirteen centres for addiction treatment in Catalonia, Spain. All subjects were evaluated with validated instruments and ad hoc questionnaires. The sample was divided into 3 groups according to how the substance consumption pattern changed during lockdown (maintained pattern, worsened pattern, and improved pattern). <b><i>Results:</i></b> More than 62% of the patients maintained or worsened their consumption pattern during confinement, and about 38% improved throughout this time. Diverse factors were associated with the changes in pattern like age, addiction severity, psychological distress during lockdown, social and familial issues, and therapeutic variables. <b><i>Conclusion:</i></b> The home lockdown during the COVID-19 pandemic was associated with major implications for substance consumption and psychiatric distress among SUD outpatients. Considering this, the need to plan appropriate interventions in cases of similar health crises is highlighted.