Introduction Sarcopenia and osteoporosis are progressive, age-related conditions that often coexist in older adults, resulting in a combined syndrome known as osteosarcopenia. This condition is characterized by a decline in bone mineral density (BMD) and skeletal muscle mass, contributing to increased functional impairment and diminished quality of life. While pharmacological agents such as alendronate are used in the management of osteoporosis, there are currently no Food and Drug Administration (FDA)-approved treatments that specifically address sarcopenia. This study explores the therapeutic potential and safety of incorporating nandrolone decanoate, an anabolic steroid, into an alendronate regimen for the management of osteosarcopenia. Methodology This prospective, single-center study was conducted at a tertiary care spine hospital in India. The study enrolled 100 postmenopausal women between the ages of 45 and 80, all diagnosed with osteoporosis using dual-energy X-ray absorptiometry (DEXA). Each participant received intramuscular nandrolone decanoate at a dose of 50 mg every three weeks for 12 weeks, followed by four-weekly injections. This regimen was administered alongside weekly oral alendronate for one year. All participants also received routine calcium and vitamin D supplementation. Assessments were performed at baseline and after 12 months, including DEXA scans to evaluate BMD, lean body mass, and fat mass. Patient-reported outcomes were captured using the Oswestry Disability Index (ODI), Visual Analog Scale (VAS), and a standardized Quality of Life Score (QoLS). Adverse events were recorded at 3, 6, and 12 months to evaluate treatment safety. Results A total of 89 out of the 100 enrolled participants completed the study. Baseline assessments revealed median BMD T-scores of -3.1 at the lumbar spine and -2.9 at Ward's triangle. The mean lean body mass was 31,984.07 g, while the mean total body fat mass was 25,966.96 g. After 12 months, BMD significantly improved at both the lumbar spine and hip. Lean body mass increased from 31,984 to 33,062 g, while total fat mass decreased slightly, although the change was not statistically significant. Patient-reported outcomes revealed substantial improvement in back pain (VAS), disability (ODI), and QoLS. No adverse events were recorded throughout the study period. Conclusion The incorporation of nandrolone decanoate with alendronate therapy significantly improved lean body mass, BMD, and patient-reported outcomes among postmenopausal women with osteosarcopenia. This therapeutic combination exhibited an excellent safety profile, with no adverse events recorded throughout the study period. These findings highlight the potential of nandrolone decanoate as an effective adjunct in the integrated management of osteoporosis and sarcopenia, contributing to improved overall patient health outcomes. However, further longitudinal studies are required to assess the long-term safety and efficacy of this therapeutic approach.