Yes, ED pills can cause side effects. In trials of the drug, individuals taking Cialis saw a significant reduction in the frequency and urgency of urination and improved urine flow. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. Brand-name versions of the drug approved for PAH include Adcirca. Cialis tadalafil : This ED medication works with the same principle as Viagra, but lasts up to 36 hours.Side Effects. Headache, stomach upset, back pain, muscle pain, stuffy nose, flushing, or dizziness may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. To. Compare prices and print coupons for Tadalafil (Cialis) (Generic Cialis) and other drugs at CVS, Walgreens, and other pharmacies. Prices start at $ Welcome! 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.