You can take sildenafil with or without food. Tell your doctor if any of these symptoms are severe or do not go away: headache. The trial results revealed that sildenafil had improved the patients’ depression, anxiety, and self-esteem. What should I do if I forget a dose? The result of smooth muscle cell target protein phosphorylation is a decrease in intracellular calcium, increased efflux of potassium, and deactivation of myosin light chain kinase, ultimately causing smooth muscle relaxation. · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose. Men will no longer require a prescription to obtain the impotence drug Viagra and will instead be able to buy it over the counter at pharmacies. The decision by the UK Medicines and Healthcare. Currently, there are no over the counter alternatives to Viagra available. Viagra (sildenafil) is a prescription medication, meaning it’s not available over the counter from your local.