You ought not modify your dose without speaking with your provider first. There is no research to ascertain whether use of tadalafil is effective or safe in patients with retinitis pigmentosa, and use in these patients is not recommended. Tadalafil does not exhibit harm to the fetus in animal studies; however, it is not studied in pregnant or nursing women. As there are no sufficient and well-controlled human studies, tadalafil should be used in pregnancy only when evidently needed, and caution should be exercised in nursing women. It really is expected that most medical health insurance plans will pay part of the cost of this medication.