Viagra 25 mg is used to get treatment for men's problems in the penis. Get it from Careskit at a low price with free home delivery.About 1 in 4 said their ED symptoms started between the ages of 50 to 59. Two in five men reported their symptoms started between age 60 and 69. Because 100mg is the highest dose available, you should never 'double up' on tablets or take more than one in 24 hours. Sildenafil 100mg is the highest safe dosage you can take – if it is ineffective, you should try another ED treatment. The effects of Viagra last one to four hours, depending on factors such as your age, medical condition, and prescribed dose. Studies have shown that if you sleep after taking Viagra, you may experience a significant increase in nighttime erections.