Dear Mr. Olan Camp, Hi & Welcome. Incomplete data like age, purpose of taking Proscar, any associated medical illness or symptoms, or medications intake, etc.??? Proscar (Finasteride) used to treat benign prostatic enlargement is unlikely to cause light to dark brown semen. The normal semen tends to be a milky white color in healthy men. The light to dark brown semen is suggestive of blood in your semen (haemospermia). It can be due to cancer of the prostate or reproductive organs or bladder. Other causes include infection like prostatitis, & sexually transmitted diseases, benign prostatic enlargement or trauma (usually involving catheterization). So, I advise you to consult a urologist for thorough evaluation and to find the exact underlying cause of blood in the semen and its treatment accordingly. Meanwhile avoid taking any blood thinners like Aspirin or Warfarin if you are taking since they can cause more bleeding. Hope this will help. A feedback is appreciated.