They may also include frequent urges to urinate. But if your symptoms are severe, call or go to the nearest emergency room right away. Never try to catch up by taking two doses erection once. This could cause dangerous side effects. Before prescribing tadalafil, your doctor may do blood tests. These tests will check how well your liver and kidneys are working. Your doctor may start you on a lower dosage of tadalafil, have you take it less often, or Generic Viagra prescribe it at all for you. This is because the symptoms of BPH and prostate cancer can be similar. Not every pharmacy stocks this drug.