Use of a diaminophenothiazine compound in the manufacture of a medicament to inhibit or reverse the aggregation of synuclein, wherein the aggregation is associated with a disease state manifested as neurodegeneration and\or clinical dementia, which disease is selected from: Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, drug-induced parkinsonism; pure autonomic failure, and wherein said medicament is for the treatment of said disease state, and wherein in said treatment the diaminophenothiazine compound is administered orally as either: (i) dosage units of about 10, 20, 30, 40, 50, 60, 80, 90, 100, 110, 120, or 130 mg three times a day; or (ii) dosage units of about 10, 20, 30, 40, 50, 60, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200 mg twice a day; or(iii) a dosage of less than or equal to 400 mg total daily dose, wherein said compound is selected from compounds of the following formulae: wherein each one of R 1, R 2, R 4, R 6, R 8, and R 9 is independently selected from: -H; -F; -CI; -Br; -I; -OH; -OR; -SH; -SR; -NO 2; -C(=O)R; -C(=O)OH; -C(=O)OR; -C(=O)NH 2; -C(=O)NHR; -C(=O)NR 2; -C(=O)NR N1 R N2; -NH 2; -NHR; -NR 2; -NR N1 R N2; -NHC(=O)H; -NRC(=O)H; -NHC(=O)R; -NRC(=O)R; -R; wherein each R is independently selected from: unsubstituted aliphatic C 1-6 alkyl; substituted aliphatic C 1-6 alkyl; unsubstituted aliphatic C 2-6 alkenyl; substituted aliphatic C 2-6 alkenyl; unsubstituted C 3-6 cycloalkyl; substituted C 3-6 cycloalkyl; unsubstituted C 6-10 carboaryl; substituted C 6-10 carboaryl; unsubstituted C 5-10 heteroaryl; substituted C 5-10 heteroaryl; unsubstituted C 6-10 carboaryl-C 1-4 alkyl; substituted C 6-10 carboaryl-C 1-4 alkyl; wherein, in each group -NR N1 R N2, independently, R N1 and R N2 taken together with the nitrogen atom to which they are attached form a ring having from 3 to 7 ring atoms; and wherein, in each group -NR 3NA R 3NA: each one of R 3NA and R 3NB is independently selected from: -H; unsubstituted aliphatic C 1-6 alkyl; substituted aliphatic C 1-6 alkyl; unsubstituted aliphatic C 2-6 alkenyl; substituted aliphatic C 2-6 alkenyl; unsubstituted C 3-6 cycloalkyl; substituted C 3-6 cycloalkyl; unsubstituted C 6-10 carboaryl; substituted C 6-10 carboaryl; unsubstituted C 5-10 heteroaryl; substituted C 5-10 heteroaryl; unsubstituted C 6-10 carboaryl-C 1-4 alkyl; substituted C 6-10 carboaryl-C 1-4 alkyl; or: R 3NA and R 3NB taken together with the nitrogen atom to which they are attached form a ring having from 3 to 7 ring atoms; and wherein the group -NR 7NA R 7NB is the same as -NR 3NA R 3NB; and wherein X- is one or more anionic counter ions to achieve electrical neutrality; and pharmaceutically acceptable salts, mixed salts, hydrates, and solvates thereof. (i) dosage units of about 10, 20, 30, 40, 50, 60, 80, 90, 100, 110, 120, or 130 mg three times a day; or (ii) dosage units of about 10, 20, 30, 40, 50, 60, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200 mg twice a day; or(iii) a dosage of less than or equal to 400 mg total daily dose, -H; -F; -CI; -Br; -I; -OH; -OR; -SH; -SR; -NO 2; -C(=O)R; -C(=O)OH; -C(=O)OR; -C(=O)NH 2; -C(=O)NHR; -C(=O)NR 2; -C(=O)NR N1 R N2; -NH 2; -NHR; -NR 2; -NR N1 R N2; -NHC(=O)H; -NRC(=O)H; -NHC(=O)R; -NRC(=O)R; -R; unsubstituted aliphatic C 1-6 alkyl; substituted aliphatic C 1-6 alkyl; unsubstituted aliphatic C 2-6 alkenyl; substituted aliphatic C 2-6 alkenyl; unsubstituted C 3-6 cycloalkyl; substituted C 3-6 cycloalkyl; unsubstituted C 6-10 carboaryl; substituted C 6-10 carboaryl; unsubstituted C 5-10 heteroaryl; substituted C 5-10 heteroaryl; unsubstituted C 6-10 carboaryl-C 1-4 alkyl; substituted C 6-10 carboaryl-C 1-4 alkyl; -H; unsubstituted aliphatic C 1-6 alkyl; substituted aliphatic C 1-6 alkyl; unsubstituted aliphatic C 2-6 alkenyl; substituted aliphatic C 2-6 alkenyl; unsubstituted C 3-6 cycloalkyl; substituted C 3-6 cycloalkyl; unsubstituted C 6-10 carboaryl; substituted C 6-10 carboaryl; unsubstituted C 5-10 heteroaryl; substituted C 5-10 heteroaryl; unsubstituted C 6-10 carboaryl-C 1-4 alkyl; substituted C 6-10 carboaryl-C 1-4 alkyl;