Never take an extra dose to make up for a forgotten one. It can be a sign of a thickening of the blood vessels as well as other conditions, so you may need further tests. You can take it up to 4 hours before you want to have sex. There are many other treatments for erectile dysfunction. The products discussed in this site may have different product labeling in different countries. If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when you get sexually excited. It is not recommended for use in Australia.There is not a great deal of difference between Sildenafil mg and 50mg, although in clinical trials, the higher dosage was seen to be 82% effective, as opposed to 74% effective. The effects of Sildenafil mg do not last longer than the 50mg dosage, but they tend to be stronger. This means that side effects can be more pronounced as well.  · Is Viagra prescribed in dosages of mg, mg, or mg? The highest recommended Viagra dose for treating erectile dysfunction (ED) is mg per day, according to the drug’s manufacturer. Viagra® 16 tablets: from £ Viagra® 28 tablets: from £ Viagra® 40 tablets: from £ Viagra® 56 tablets: from £ Viagra Connect® 2 tablets: £ Viagra Connect® 4 tablets: £ Viagra Connect® 8 tablets: £ Viagra Connect® 12 tablets: £ Viagra Connect® 16 tablets: £ Viagra Connect.