The building blocks of English

Affixes

-ergic

Involving, releasing, or mimicking a specified substance as a neurotransmitter.

Greek ergon, work, plus ‑ic.

Some examples: adrenergic, relating to or denoting nerve cells in which adrenalin or a similar substance acts as a neurotransmitter, as contrasted with cholinergic cells, in which acetylcholine acts as a neurotransmitter; dopaminergic, releasing or involving dopamine as a neurotransmitter; purinergic, involving a purine derivative; peptidergic, designating a neurone which releases one or more particular neuropeptides when stimulated.

The same root is present in synergic (from synergy, the creation of something greater than the sum of its parts). However, in lysergic (as in lysergic acid diethylamide or LSD) the root is ergot, a fungal disease of cereals; in allergic the ending is an accident of spelling.