Kim Stanley Robinson deals with a lot of these issues in his sci fi trilogy about the colonization of Mars (Red Mars, Green Mars, Blue Mars), where the life-extending treatment is invented and provided to the colonists of Mars. It's fascinating and if you ever wondered about this idea, you should get these books and read them, especially the first two. In his portrayal of this process it seems the most prevalent side effect is memory loss, which makes sense. Also this type of thing needs to be paired with strict population control measures, which he also goes into in a very elegant way (every person granted the implicit right to bear 0.75 children, licencing off the other 0.5 or buying it from another couple that does not want it, etc.)