A chemical agent obtainable from a plant of the Euphorbiaceae family or a derivative or chemical analogue or a pharmaceutically compatible salt thereof which chemical agent, derivative or chemical analogue is a macrocyclic diterpene selected from compounds of the ingenane family represented by general formula wherein:- R 24, R 25 and R 26 are independently selected from hydrogen, OH, OR 27 or X(C=X)R 29 where X is oxygen; each R 27 is independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy, C 1 -C 10 alkyl which is substituted by CN, OR 27', SR 27', NR 27' R 28', N(=O) 2, NR 27' OR 28', ONR 27' R 28', SOR 27', SO 2 R 27', SO 3 R 27', SONR 27' R 28', SO 2 NR 27' R 28', SO 3 NR 27' R 28', P(R 27') 3, P(=O)(R 27') 3, Si(R 27') 3, or B(R 27') 2; R 27' and R 28' are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy; R 29 is R 27; and which chemical agent, derivative or chemical analogue or pharmaceutically compatible salt thereof is capable of modulating PKC activity, PKC-gene expression or PKC enzyme turnover for use in the treatment or prophylaxis of a PKC-related condition or disorder in a subject, wherein the PKC-related condition is alcoholism, Alzheimer's disease, asthma, atherosclerosis, atopic dermatitis, autoimmune disease, bipolar disorder, blood disorder, cardiac hypertrophy, depression, diabetes, hypertension, hyperplastic dermatosis, multiple sclerosis, mycardial ischemia, osteoarthritis, psoriasis, rheumatoid arthritis, transplantation or latent virus and wherein said chemical agent, derivative or chemical analogue or pharmaceutically compatible salt thereof is for administration for a time and under conditions sufficient to ameliorate one or more symptoms associated with the PKC-related condition or disorder. R 24, R 25 and R 26 are independently selected from hydrogen, OH, OR 27 or X(C=X)R 29 where X is oxygen; each R 27 is independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy, C 1 -C 10 alkyl which is substituted by CN, OR 27', SR 27', NR 27' R 28', N(=O) 2, NR 27' OR 28', ONR 27' R 28', SOR 27', SO 2 R 27', SO 3 R 27', SONR 27' R 28', SO 2 NR 27' R 28', SO 3 NR 27' R 28', P(R 27') 3, P(=O)(R 27') 3, Si(R 27') 3, or B(R 27') 2; R 27' and R 28' are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy; R 29 is R 27; and which chemical agent, derivative or chemical analogue or pharmaceutically compatible salt thereof is capable of modulating PKC activity, PKC-gene expression or PKC enzyme turnover for use in the treatment or prophylaxis of a PKC-related condition or disorder in a subject, wherein the PKC-related condition is alcoholism, Alzheimer's disease, asthma, atherosclerosis, atopic dermatitis, autoimmune disease, bipolar disorder, blood disorder, cardiac hypertrophy, depression, diabetes, hypertension, hyperplastic dermatosis, multiple sclerosis, mycardial ischemia, osteoarthritis, psoriasis, rheumatoid arthritis, transplantation or latent virus and wherein said chemical agent, derivative or chemical analogue or pharmaceutically compatible salt thereof is for administration for a time and under conditions sufficient to ameliorate one or more symptoms associated with the PKC-related condition or disorder.