March 20 (Reuters) - Nektar Therapeutics said its experimental opioid, designed to achieve pain relief minus the high levels of euphoria that can lead to abuse and addiction with existing opioids, succeeded in a key late-stage study.

The drug, which by design reaches the brain slower than existing opioids to deter abuse, outperformed a placebo in over 600 patients with chronic lower back pain.

(Reporting by Natalie Grover in Bengaluru; Editing by Anil D'Silva)