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Background Pharmacogenetics is the study of variability in drug response caused by genetic variations. It is estimated that over two million hospitalized patients develop severe adverse drug reactions in the United States annually, incurring a direct medical cost of 200 billion US dollars (USD). This indicates a huge potential in reducing healthcare costs even if only a small proportion of adverse drug reactions are preventable by genotype-guided prescription. The current clinical applications of pharmacogenetics are mostly limited to reactive pharmacogenetic testing, in which investigations are ordered only when certain high-risk medications are prescribed, or after an adverse drug reaction has occurred. In contrast, preemptive pharmacogenetic testing allows the optimization of dosing based on genotype information at the time of prescription, minimizing the risk of undesired outcomes. Objectives Pharmacogenetics (PGx) encompasses the potential to improve therapeutic response and reduce adverse drug reaction in the era of precision medicine. However, Chinese PGx data is limited. To address this issue, we examined the spectrum of 133 actionable pharmacogenetic variants and rare deleterious variants in 108 pharmacogenes and estimated the proportion of dispensed drugs that may potentially benefit from genotype-guided prescriptionusing an exome sequencing (ES) cohort. Methods Secondary analysis of ES data was conducted to study pharmacogenetics in 1116 HK Chinese, which included 622 males and 494 females. The projected preemptive pharmacogenetic testing prescription impact was evaluated based on the patient prescription data between January 1, 2019 and December 31, 2019 in the HK public healthcare system, serving 7.5 million people and accounting for approximately 90% of all secondary and tertiary healthcare services provided. Results Twenty-nine actionable pharmacogenetic variants/alleles were identified in our cohort. Nearly all (99.6%) subjects carried at least one actionable pharmacogenetic variant, with a median of four variants, whereas 93.5% of subjects harbored at least one rare deleterious pharmacogenetic variant, with a median of two variants. The frequency of actionable genotypes was the highest in recipients of clopidogrel (57.21%), tacrolimus (43.38%), and warfarin (43.13%). Based on the prescription data of the public healthcare system in 2019, 13.4% of the HK population was prescribed with drugs with implicated actionable pharmacogenotypes in the HK population. The total expenditure on actionable drugs was 33,520,000 USD, and it was estimated that 8,219,000 USD (24.5%) worth of drugs were prescribed to patients with an implicated actionable genotype. Conclusions In conclusion, nearly all individuals carried at least one actionable pharmacogenetic variant and one rare, deleterious pharmacogenetic variant in our cohort. It was estimated that oneseventh of the HK population received at least one of the 36 drugs with CPIC guideline recommendations, and 8,219,000 USD worth of drugs were prescribed to patients with an implicated actionable genotype. The results showed that secondary use of ES data is feasible for pharmacogenetic analysis, and preemptive pharmacogenetic testing has the potential to support prescription decisions in inpatient and specialist outpatient settings in the HK Chinese population.