does anastrazole make heart and genital muscles stiff

The short version: anastrozole is linked to joint stiffness and musculoskeletal pain, but the evidence for heart muscle stiffness or genital muscle stiffness specifically is thin to absent.

The evidence you have is almost entirely about women with breast cancer taking anastrozole. The largest trial, the ATAC study, found that 27.8% of women on anastrozole reported musculoskeletal events, compared to 21.2% on tamoxifen [2]. A smaller study of 53 women found that 26% developed joint symptoms, with digital stiffness being the most common complaint, appearing at a median of 5 months [7]. The mechanism is not fully understood, but it is clearly a real and common side effect. The evidence does not describe the stiffness as affecting the heart or genital muscles specifically. The case report of vasculitis (inflammation of blood vessels) from anastrozole is a different process from muscle stiffness [3].

For the heart, the evidence on lipids is mixed. One study found anastrozole raised HDL cholesterol (the "good" kind) by about 7% over 12 months, but had no significant effect on LDL or triglycerides [4]. That is not the same as heart muscle stiffness, which is a condition like cardiomyopathy. There is no evidence in these records that anastrozole causes that. For genital muscles, the evidence is also absent. The only study touching on sexual function was a pilot trial of vaginal testosterone cream for women on aromatase inhibitors who had sexual dysfunction, which implies the drug itself can cause problems, but it does not name muscle stiffness as the cause [10].

My call: anastrozole commonly causes joint and digital stiffness, but the evidence does not support that it causes stiffness of heart or genital muscles. Confidence: moderate for joint stiffness, low for heart or genital muscle stiffness.