The categories overlap. Neuropeptides can function as neurotransmitters, so the clearest comparison is between small-molecule neurotransmitters and peptide transmitters. Both help cells communicate, but they often differ in production, storage, release and timing.

Two broad styles of chemical signaling

Small-molecule transmitters include substances such as glutamate, GABA and acetylcholine. Peptide transmitters are amino-acid chains processed from larger precursors. Many neurons use more than one messenger, allowing rapid signals and slower modulation to interact. NCBI Bookshelf: Neurotransmitters

A useful analogy is the difference between a brief command and a change in operating settings. A rapid transmitter may help trigger an immediate response, while a peptide can adjust how readily the network responds to later signals. The analogy is only a guide: actual timing and effects depend on receptors and circuits.

Their production and removal can differ

Peptides generally require synthesis and processing of precursor proteins and transport within the neuron. After release, enzymes can break them into inactive fragments. Small-molecule transmitters use other combinations of synthesis, recycling, reuptake and degradation. NCBI Bookshelf: The neuropeptides

Why the distinction matters

Calling a substance a neuropeptide does not make it more advanced, more natural or safer than another transmitter. Nor does it mean adding more will improve communication. The nervous system depends on location, timing and balance, not simply the amount of a messenger.

When a study reports a peptide-related effect, look at the receptor and outcome rather than assuming all peptide signaling works the same way. The most useful scientific descriptions explain how the specific molecule interacts with the specific circuit being studied.