In the report the Special Rapporteur addresses the overall violence and the criminal situation in Mexico including substantial drug-production and trafficking, including political support of armed groups (paragraph 75).
The report also lists cases where drugs played a role in the torture/inhumane treatment (starting from page 29 of the table of cases).
Citation: Nigel Rodley, 'Report of the Special Rapporteur on torture and other cruel, inhuman or degrading treatment or punishment: Visit to Mexico' (1998) E/CN.4/1998/38/Add.2