Sigmaergics

Ligands at the sigma receptors. The name is a historical accident: σ₁ was first taken for an opioid receptor subtype and is nothing of the kind — it is a chaperone protein at the endoplasmic reticulum membrane, modulating calcium signalling and the trafficking of other receptors — and σ₂ turned out to be an unrelated protein again. Because a sigma ligand modulates rather than opening or blocking a channel of its own, reported effects vary with what else is happening in the cell, and one ligand's profile predicts little about another's.

Sigma binding on its own is not what puts a substance here. Many drugs already filed elsewhere on this tree bind sigma sites incidentally — dissociatives, stimulants, antidepressants and antipsychotics among them. This family is for compounds whose sigma activity is the reason they are taken, not for every compound that happens to touch the receptor.