If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately. Study Variables The dependent variable was the use of sildenafil citrate for recreational purposes and this was analyzed against the independent variables; socio-demographic factors age, marital status, partner status, educational status, occupation, religion and other factors such as illicit substance use, and duration of sildenafil use. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. Remove the cap by pushing it down and twisting it counter-clockwise. Kidney disease, severe or Liver disease, severe—Use with caution.This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So. Free Shipping · Discreet Packaging · Personalized Plan · Real DoctorsAmenities: Premature Ejaculation, Men’s Health, FDA APPROVED, Telemed. Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg strengths. The usual adult dose is 20mg taken 3 times a day. Doses for children can range from 10mg to 20mg taken 3 times a day, depending on their weight. Do not take it more than 3 times a day.