For many pain relievers, particularly opioids, tolerance to the medications over time can limit their long-term effectiveness and require higher doses of medication to achieve the same level of pain relief. In this study, the modified compound offered prolonged pain relief -- the animals showed no signs of developing tolerance despite twice-daily treatments with the compound over the course of nine days. This is a promising sign that the molecule could be used as a non addictive drug for relief of chronic pain, which requires continued treatment over time.