Background/Objectives: Malnutrition and undernutrition are critical health concerns associated with increased mortality and costs. Although these are distinct clinical concepts, they are often used interchangeably in clinical practice and are inconsistent with the diagnostic frameworks. This diagnostic ambiguity may obscure true patient profiles. This study aimed to clarify the real-world diagnostic patterns of malnutrition and undernutrition and identify associated drug prescription trends using a patient estimation database in Japan. Methods: We analyzed the AHI partners database of 2024. Patients were identified using the International Statistical Classification of Diseases and Related Health Problems, 10th Revision, code E46. Sex differences were analyzed and stratified according to age group: older adults (≥65 years) and younger adults (15–39 years). Odds ratios (ORs) were used to identify associated drugs. Results: Of 96,673,453 patients, 216,652 were diagnosed with malnutrition and 77,100 with undernutrition. In both categories, older adults accounted for more than half of the patients. Notably, distinct diagnostic labeling patterns were observed by sex. Malnutrition predominated in women (58.8%), whereas undernutrition was more prevalent in men (70.6%). This male predominance of undernutrition was reversed in younger adults, where women showed higher proportions in both categories. Prescription analysis identified 31 drugs frequently prescribed to the study population. Enteral elemental formulas had the highest OR (89.7). Some psychotropic drugs were frequently prescribed to women. Conclusions: Diagnostic patterns varied by sex and age, potentially reflecting distinct practices in diagnostic labeling. These findings highlight the need for standardized frameworks to ensure consistent assessments and effective nutritional interventions.

“Triple whammy” prescriptions, combining non-steroidal anti-inflammatory drugs (NSAIDs), renin–angiotensin system (RAS) inhibitors, and diuretics, increase acute kidney injury (AKI) risk. To clarify the frequency and profiles of these prescriptions and identify vulnerable populations, we analyzed the AHI partners database to estimate the number of individuals prescribed these three drug classes. In the single-agent analysis, loxoprofen was the most commonly prescribed NSAID (66.3%), olmesartan (19.4%) and telmisartan (15.9%) were the predominant RAS inhibitors, and furosemide (19.6%) and spironolactone (16.0%) were the most frequently used diuretics. Dual-drug combinations showed patterns consistent with the single-agent results for NSAIDs and diuretics. By contrast, sacubitril/valsartan was the most common RAS inhibitor when combined with diuretics, frequently utilized for heart failure management. In triple whammy prescriptions, NSAIDs and diuretics patterns mirrored those of single-agents. The annual number of triple whammy prescriptions showed a statistically significant downward trend over the study period by the Mann–Kendall trend test (p = 0.048). Notably, sacubitril/valsartan was the leading RAS inhibitor (46/199 patients, 23%), showing a higher proportion than its single-agent use (7.4%). Heart failure patients prescribed these two causative drugs are highly vulnerable to “triple whammy” prescriptions. Awareness of inadvertent NSAID additions is warranted to mitigate potential AKI risks.