A pharmacotherapy is provided for preventing glaucoma or preventing or treating ocular hypertension, the pharmacotherapy providing potent intraocular pressure-lowering action with fast-acting properties and prolonged duration. A combination of (S)-(−)-1-(4-fluoro-5-isoquinolinesulfonyl)-2-methyl-1,4-homopiperazine or a salt thereof, or a solvate of (S)-(−)-1-(4-fluoro-5-isoquinolinesulfonyl)-2-methyl-1,4-homopiperazine or the salt thereof and an α2 agonist for preventing or treating glaucoma.