5-HT	5-hydroxytryptamine
Ach	Acetylcholine
AIDS	Acquired Immune Deficiency Syndrome
BDNF	Brain Derived Neurotrophic Factor
CNS	Central Nervous System
DOR	δ-opioid receptors
ENS	Enteric Nervous System
FMT	Faecal Microbiota Transplantation
GI	Gastrointestinal
HCV	Hepatitis C Virus
HIV	Human Immunodeficiency Virus
HPA	Hypothalamus Pituitary Axis
HSV	Herpes Simplex Virus
IBD	Irritable Bowel Disease
MLCK	Myosin Light Chain Kinase
MOR	μ-opioid receptors
NMDA	N-methyl-D-aspartate
OIBD	Opioid-Induced Bowel Dysfunction
OIC	Opioid Induced Constipation
OID	Opioid Induced Dysbiosis
OIH	Opioid-Induced hyperalgesia
OUD	Opioid Use Disorder
PAMORA	Peripherally Acting μ Opioid Receptor Antagonists
PNS	Peripheral Nervous System
QSP	Quantitative Systems Pharmacology
RVM	Rostral Ventromedial Medulla
TLR	Toll-Like Receptor
VIP	Vasoactive Intestinal Peptide