Things that can cause a false-positive test for opioids on a urine drug screen
Dextromethorphan, diphenhydramine, ibuprofen, and even fluoroquinolones are among the many agents that can cause a false-positive urine drug screen for opioids.
Pseudoephedrine can cause a false-positive test for amphetamines
Further Reading / References
Pitfalls & pearls for 8 common lab tests. J Fam Pract 2014;63(4):198-205.
Urine drug screening: A valuable office procedure. Am Fam Physician 2010;81(5):635-640.
Jamison RN, Mao J: Opioid analgesics. Mayo Clin Proc 2015;90(7):957-968.