The Screen-Well® opioid and sigma ligands plate contains 74 ligands including endogenous neurotransmitters, agonists, antagonists, and marketed drugs. The library is ideal for screening or identifying recombinant orphan G protein coupled receptors, target validation, secondary screening, assay development, and other pharmacological applications. The opioid and sigma ligands plate is 1 plate of the larger Neurotransmitter Library which contains over 650 ligands.