A 60-year-old man in Warsaw, Poland, presented a peculiar diagnostic dilemma. He had been vomiting for two days and had lost 40 pounds (18 kilograms) over the previous year without dieting. Doctors initially treated him with a diuretic, intravenous fluids, a steroid, and a calcium-lowering drug. While his calcium levels briefly improved, they soon rose again, leading to his admission to a nephrology ward. The patient’s medical history revealed a crucial detail: he had been receiving ‘unknown intramuscular injections’ containing testosterone to enlarge his chest and upper-arm muscles. The last dose was administered two years prior, but the frequency of these injections was unclear. Blood tests showed low parathyroid hormone levels, ruling out a common hormonal cause of high calcium. The patient had no signs of digestive tract cancers, urological abnormalities, or autoimmune conditions. A biopsy of the abnormal muscle regions revealed a silicone-like, oil-based substance surrounded by dense calcium deposits, indicating the presence of synthol, a muscle-bulking agent made of oil. The synthol injections had triggered a foreign-body reaction, leading to scarring and calcification, which eventually entered his bloodstream. The rarity of this case and the delayed onset of symptoms made diagnosis challenging. Only two other cases of high blood calcium linked to synthol injections had been reported, both from Lebanon. The authors emphasized that synthol injections can cause elevated serum calcium levels, despite their infrequent occurrence. This case highlights the potential risks of synthol, including muscle deformity, chronic wounds, and scarring, and the importance of understanding its long-term effects.