Tell your doctor if any of these symptoms are severe or do not go away: headache. Do not take a double dose or more than one dose per day to make up for a missed one. 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. Conclusion Navigating the vast ocean of medical treatments can be daunting. One advantage Cialis has over Viagra and Levitra is its Tadalafil can be synthesized starting from D – tryptophan methyl ester and piperonal via a Pictet—Spengler reaction. Before taking tadalafil, tell your doctor and pharmacist if you are allergic to tadalafil, any other medications, or any of the ingredients in tadalafil tablets.Cialis. Cialis 40/20mg, packs of 10 – Pills. The sexual enhancer Cialis is mainly used by men with medically diagnosed erectile dysfunction. This is when the erection is not sufficient for satisfactory sexual intercourse. The drug requires a prescription and is only dispensed in pharmacies against a prescription. Check Price. Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash. Tadalafil, or generic Cialis, is most commonly used to treat erectile dysfunction (ED). However, it’s also used to treat benign prostatic hyperplasia (BPH) and pulmonary arterial hypertension.