[Leu5]-Enkephalin, amide is a δ opioid receptor agonist. Enkephalin, one of several naturally occurring morphinelike substances (endorphins) released from nerve endings of the central nervous system and the adrenal medulla.

Quaternary ammonium analog of ethidium; an intercalating dye with a specific affinity to certain forms of DNA and, used as diiodide, to separate them in density gradients.

Quazolast (RHC 3988) is a potent mediator release inhibitor used as a control against ragweed antigenic nasal challenge and demonstrates superiority over placebo in preventing nasal congestion and nasal itching following such challenges.