Consort flow diagram.

The test stimulus temperatures (heat pain) as determined prior to treatment averaged to 47 ± 0.5°C, 46.6 ± 0.5°C and 46.9 ± 0.5°C on placebo, morphine and tapentadol experimental sessions (one-way anova: NS). The target conditioning stimulus temperatures were 7.9 ± 0.5°C, 8.1 ± 0.6°C and 8.3 ± 0.6°C on placebo, morphine and tapentadol experimental sessions (one-way anova: NS).