Mechanism of action[ edit ] Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and the smooth muscle of the corpus cavernosum. Tadalafil is in a class of medications called phosphodiesterase PDE inhibitors. Do not take a double dose or more than one dose per day to make up for a missed one. Symptoms may include sudden urges to urinate urgency , difficulty in starting urination hesitancy , a weak urine stream, and more frequent urination — especially at night. It works best when taken one hour before sex. If you are taking tadalafil for erectile dysfunction, your doctor will probably start you on an average dose of tadalafil and increase or decrease your dose depending on your response to the medication. Society and culture[ edit ] Marketing[ edit ] Cialis 5mg UK pack of 28 tablets In the United States, the FDA relaxed rules on prescription drug marketing in , allowing advertisements targeted directly to consumers.Tadalafil is in a class of medications called phosphodiesterase (PDE) inhibitors. It works to treat erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection. Tadalafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow more easily. heart attack symptoms – chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating. Common tadalafil side effects may include: headache; flushing (warmth, redness, or tingly feeling); nausea, upset stomach; stuffy nose; or. muscle pain, back pain, pain in your arms, legs, or back. This is not a complete list of side. milligrams (mg) 5 mg 10 mg 20 mg The cost for these different strengths depends on whether you have insurance, your individual plan coverage, and .