Cialis is the trade name and the generic name is tadalafil. Taking tadalafil 5mg per day does not work and may be caused by insufficient dosage of the medication, lack of sexual stimulation and so on. 1. Insufficient dosage: Tadalafil is a drug for treating erectile dysfunction in men, and the general recommended dosage is 10mg, so taking 5mg may not work because of insufficient dosage. 2. No sexual stimulation: Tadalafil requires sexual stimulation for the drug to take effect, so without sexual stimulation, you may not be able to get an erection. Tadalafil must be guided by a doctor to use the drug, the patient can not be arbitrary use of drugs, and must strictly comply with the doctor’s instructions, on time and according to the dosage of the drug, the drug to pay attention to the drug ingredients allergic to those who are prohibited.