Among the people who should not take tadalafil are those who are allergic to tadalafil or any of its inactive components and those taking a nitrate for angina. Also, problems with the heart, brain, and blood vessels can occur in some people taking tadalafil. A few other precautions and warnings for tadalafil include potential drug interactions, conditions to let your healthcare provider know about before you take tadalafil (including liver disease or failure), and the risk of a prolonged and sometimes painful erection (lasting longer than four hours) in some people taking this medicine.

• Low blood pressure (hypotension)
• High blood pressure (hypertension)
• Heart disease, such as angina, congestive heart failure, or irregular heartbeats
• Multiple myeloma
• Kidney disease or kidney failure
• Liver disease or liver failure
• A history of a heart attack, stroke, or life-threatening arrhythmia within the past three months
• Retinitis pigmentosa, which is a rare eye problem
• A history of severe vision loss, including a condition called NAION
• Stomach ulcers
• Other bleeding problems
• Sickle cell anemia
• Leukemia
• A history of priapism, which is a painful erection lasting longer than six hours
• Any condition that causes a penis deformation, such as angulation, Peyronie's disease, or cavernosal fibrosis
• Any allergies.