[Neuroscience] What exactly are neuromodulators?

[alex]

Are neuromodulators secreted by neurons and do they bind to receptors
of the post synaptic membrane? So what is the difference between them
and neurotransmitters then? Do they affect neurontransmitters? If yes,
how do they do? Are drugs (like opiates, amphetamines) neuromodulators
or neurotransmitters?

Thanks and kind regards, alex