G protein-coupled receptor for 5-hydroxytryptamine (serotonin) (PubMed:10452531, PubMed:1315531, PubMed:1328844, PubMed:1348246, PubMed:1351684, PubMed:1559993, PubMed:1565658, PubMed:1610347, PubMed:23519210, PubMed:23519215, PubMed:29925951, PubMed:8218242). Also functions as a receptor for ergot alkaloid derivatives, various anxiolytic and antidepressant drugs and other psychoactive substances, such as lysergic acid diethylamide (LSD) (PubMed:23519210, PubMed:23519215, PubMed:29925951). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors, such as adenylate cyclase (PubMed:10452531, PubMed:1315531, PubMed:1328844, PubMed:1348246, PubMed:1351684, PubMed:1559993, PubMed:1565658, PubMed:1610347, PubMed:23519210, PubMed:23519215, PubMed:29925951, PubMed:8218242). HTR1B is coupled to G(i)/G(o) G alpha proteins and mediates inhibitory neurotransmission by inhibiting adenylate cyclase activity (PubMed:29925951, PubMed:35610220). Arrestin family members inhibit signaling via G proteins and mediate activation of alternative signaling pathways (PubMed:29925951). Regulates the release of 5-hydroxytryptamine, dopamine and acetylcholine in the brain, and thereby affects neural activity, nociceptive processing, pain perception, mood and behavior (PubMed:18476671, PubMed:20945968). Besides, plays a role in vasoconstriction of cerebral arteries (PubMed:15853772). {ECO:0000269|PubMed:10452531, ECO:0000269|PubMed:1315531, ECO:0000269|PubMed:1328844, ECO:0000269|PubMed:1348246, ECO:0000269|PubMed:1351684, ECO:0000269|PubMed:1559993, ECO:0000269|PubMed:1565658, ECO:0000269|PubMed:15853772, ECO:0000269|PubMed:1610347, ECO:0000269|PubMed:23519210, ECO:0000269|PubMed:23519215, ECO:0000269|PubMed:29925951, ECO:0000269|PubMed:35610220, ECO:0000269|PubMed:8218242, ECO:0000303|PubMed:18476671, ECO:0000303|PubMed:20945968}. This is the function of Ensembl gene identifier ENSG00000135312 (HTR1B, 5-hydroxytryptamine receptor 1B).