Objectives: To determine whether candidate pharmacodynamic ((3-adrenergic receptor) and pharmacokinetic (cytochrome P450 2D6) gene polymorphisms are associated with the intraocular pressure (IOP) response to topical β-blockers. Methods: Medical records of 18773 adults in the Personalized Medicine Research Project were searched to extract all IOP measurements for subjects who had been prescribed a topical β-blocker. Five single-nucleotide polymorphisms in the (β1-, (β2-, and (β3-adrenergic receptor genes and 6 polymorphisms in the CYP2D6 gene were genotyped. Results: A total of 58.1% of the subjects were female; the mean age was 63.8 years. Topical (3-blockers were prescribed for 343 eyes of 215 subjects. An IOP reduction of 20% or more in 1 or both eyes was observed in 61.0% of subjects. Men were significantly more likely than women to have an IOP decrease of 20% or more (69.3% vs 54.9%, respectively; ψ2=4.48; P= .04). After adjusting for sex, family history of glaucoma, and use of systemic (3-blockers, subjects with the CC genotype at coding single-nucleotide polymorphism rs1042714 in the ADRB2 gene were significantly more likely to experience an IOP decrease of 20% or more (odds ratio, 2.00; 95% confidence interval, 1.00-4.02). Conclusion: We found that a coding single-nucleotide polymorphism in ADRB2 is associated with an increased likelihood of a clinically meaningful IOP response to topical β-blockers. Clinical Relevance: Because topical β-blockers are the least expensive class of agents used to lower IOP, genotype-based drug prescribing could save health care dollars.