To evaluate the cardiorespiratory, sedative and antinociceptive effects of dexmedetomidine alone or in combination with methadone, morphine or tramadol in dogs. Experimental, blinded, randomized, crossover study. Six mixed breed dogs (two males and four females) weighing 10 ± 4 kg. The animals were randomly divided into four treatments: D (10 μg kg−1 of dexmedetomidine), DM (dexmedetomidine 10 μg kg−1 and methadone 0.5 mg kg−1); DMO (dexmedetomidine 10 μg kg−1 and morphine 0.5 mg kg−1), and DT (dexmedetomidine 10 μg kg−1 and tramadol 2 mg kg−1). The combinations were administered intramuscularly in all treatments. The variables evaluated were heart rate (HR), respiratory rate (fR), rectal temperature (RT), systolic arterial pressure (SAP), sedation scale and pedal withdrawal reflex. These variables were measured at T0 (immediately before the administration of the protocol) and every 15 minutes thereafter until T105. A decrease in HR and fR occurred in all the treatments compared with T0, but no significant difference was observed between the treatments. The RT decreased from T45 onward in all the treatments. The SAP did not show a difference between the treatments, but in the DT treatment, the SAP was lower at T30 and T45 compared with T0. The D treatment had lower scores of sedation at T15 to T75 compared with the other treatments, and the DMO and DM treatments showed higher scores at T60 and T75 compared with DT. The treatments with morphine and methadone added to the dexmedetomidine showed higher sedation scores than the control treatment and the treatment with tramadol added to the dexmedetomidine showed no relevant differences in any of the variables evaluated in the study.