Nomenclature	H1 receptor	H2 receptor	H3 receptor	H4 receptor
HGNC, UniProt	HRH1, P35367	HRH2, P25021	HRH3, Q9Y5N1	HRH4, Q9H3N8
Principal transduction	Gq/11	Gs	Gi/o	Gi/o
Selective agonists (pKi)	methylhistaprodifen (6.4) 1025, histaprodifen (5.7) 1013	amthamine (pEC50 6.4) 1008	immethridine (9.1) 1007, methimepip (9.0) 1006	clobenpropit (Partial agonist) (7.4 – 8.3) 1000,1013–1015,1019, 4-methylhistamine (7.3 – 8.2) 1001,1013, VUF 8430 (7.5) 1012
Selective antagonists (pKi)	pyrilamine (Inverse agonist) (8.7 – 9.0) 995,1023, triprolidine (8.5 – 9.0) 995,1017	tiotidine (7.5 - Rat) 994, ranitidine (7.1) 1010	clobenpropit (8.4 – 9.4) 997,1000,1011,1014,1016,1028,1029, A331440 (8.5) 1002, iodophenpropit (8.2 – 8.7) 1028,1029, thioperamide (7.1 – 7.7) 997,999,1000,1011,1016,1028,1029	JNJ 7777120 (7.8 – 8.3) 1013,1026,1027
Radioligands (Kd)	[11C]pyrilamine, [11C]doxepin (Antagonist) (1x10-9 M) 1004, [3H]pyrilamine (Antagonist, Inverse agonist) (7.9x10-10 – 4x10-9 M) 998,1017,1024,1025	[125I]aminopotentidine (Antagonist) (2x10-9 M - Rat) 1009, [3H]tiotidine (Antagonist) (2.2x10-9 – 2x10-8 M) 1018	[123I]iodoproxyfan (Antagonist) (6.3x10-11 M) 1011, [125I]iodophenpropit (Antagonist) (6x10-10 M - Rat) 1005, [3H](R)-α-methylhistamine (Agonist, Full agonist) (6x10-10 M) 1014, N-[3H]α-methylhistamine (Agonist, Full agonist) (1x10-9 M - Mouse) 996	[3H]JNJ 7777120 (Antagonist) (3.6x10-9 M) 1027