A compound of formula ( I-Ha ), or a salt, or solvate thereof: wherein R 6 is selected from the group consisting of hydrogen, - C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, and heterocycle; R' is selected from the group consisting of hydrogen, -(C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and R 7 and R 8 are independently selected from the group consisting of hydrogen, -C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; or a compound of formula ( II-Hc ), or a salt, or solvate thereof wherein R 6 is selected from the group consisting of hydrogen, - C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, and heterocycle; R' is selected from the group consisting of hydrogen, -(C 1 -C 8 )alkyl,-(C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and R 7 and R 8 are independently selected from the group consisting of hydrogen, -C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and wherein R 1 is selected from hydrogen and (C 1 -C 4 )alkyl; for use in a method for treating and/or preventing symptoms, diseases, disorders, or conditions associated with, or having etiologies involving, vitamin B3 deficiency, selected from indigestion, fatigue, canker sores, vomiting, poor circulation, burning in the mouth, swollen red tongue, depression, pellagra, Cockayne Syndrome, Neill-Dingwall Syndrome and progeria, in a subject mammal, comprising orally delivering to the mammal in need of such treatment an effective amount of at least one compound of formula ( I-Ha ) or compound of formula (II-Hc), or a salt, or solvate thereof. wherein R 6 is selected from the group consisting of hydrogen, - C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, and heterocycle; R' is selected from the group consisting of hydrogen, -(C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and R 7 and R 8 are independently selected from the group consisting of hydrogen, -C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; or a compound of formula ( II-Hc ), or a salt, or solvate thereof wherein R 6 is selected from the group consisting of hydrogen, - C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, and heterocycle; R' is selected from the group consisting of hydrogen, -(C 1 -C 8 )alkyl,-(C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and R 7 and R 8 are independently selected from the group consisting of hydrogen, -C(O)R', -C(O)OR', -C(O)NHR', (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, aryl, heteroaryl, heterocycle, aryl(C 1 -C 4 )alkyl, and heterocycle(C 1 -C 4 )alkyl; and wherein R 1 is selected from hydrogen and (C 1 -C 4 )alkyl; for use in a method for treating and/or preventing symptoms, diseases, disorders, or conditions associated with, or having etiologies involving, vitamin B3 deficiency, selected from indigestion, fatigue, canker sores, vomiting, poor circulation, burning in the mouth, swollen red tongue, depression, pellagra, Cockayne Syndrome, Neill-Dingwall Syndrome and progeria, in a subject mammal, comprising orally delivering to the mammal in need of such treatment an effective amount of at least one compound of formula ( I-Ha ) or compound of formula (II-Hc), or a salt, or solvate thereof. <EOS>