<unk>  analgesic drugs tend to exhibit incomplete cross-tolerance, so that even when a patient has developed a high level of tolerance to one drug from this class, they may find that a different<unk>  drug will still be effective. The reasons for this are still not completely understood, but are thought to result from variations in<unk>  receptor affinity and occupancy levels at equianalgesic doses, as well as additional mechanisms of action possessed by some drugs such as the NMDA antagonist action of methadone or levorphanol, or the SNRI activity of tramadol or tapentadol.
Opioid rotation
Lateral release 
Counterstimulation
Paraspinal inhibition
Co-stimulation
Neurostimulation
Burst suppression
Neural facilitation