The TGA has released a warning that an erection-enhancing drug that could pose serious health risks to users.    MMC Maxman IV Erection Enhancer capsules, sold primarily online, contain traces of sildenafil, the active ingredient in Viagra, which has a multitude of contraindications and has been linked to rare cases of stroke, heart attack, vision loss and renal failure.    A number of people in Australia have purchased the pills online in the believing they were made from herbal ingredients and contained no medicines, because the quantities of sildenafil were not declared on the product's label, the TGA said.    In Australia, sildenafil products are only available via prescription making Maxman IV not only illegal, but potentially very dangerous.    Consumers taking MMC Maxman IV Erection Enhancer have...