Finasteride is generally safe. Side effects are more common at the 5mg dosage (effective for treating benign prostatic hyperplasia, or BPH) than at the 1mg for hair loss treatment.18 But, there are possible side effects, which most commonly include lower sex drive, drop in semen volume, and erectile dysfunction. There is also a reasonable chance of increased depression, especially in men already diagnosed with the condition.19 Other side effects are more serious, but they're less common.