A chemical messenger is any compound that serves to transmit a message. A chemical messenger may refer to: 1  Hormone, Long range chemical messenger. 2  Neurotransmitter, communicates to adjacent cells.3  Neuropeptide, a protein sequence which acts as a hormone or neurotransmitter. chemical messenger may refer to: 1  Hormone, Long range chemical messenger. 2  Neurotransmitter, communicates to adjacent cells. 3  Neuropeptide, a protein sequence which acts as a hormone or neurotransmitter.