Lower levels of testosterone but higher levels of oxytocin/vasopressin have been associated with long-term relationships (e.g., couples often have less sex as they become more attached to each other). (Fisher, Helen, PhD. The First Sex. p 256-258. NY:Random House, 1999.)

Study: attachment, lust, and infatuation. Each component is characterized by specific brain chemistry. (Pease, Barbara and Allan. Why Men Don’t Have a Clue and Women Always Need More Shoes. p 226-230. NY: Broadway Books, 2004.)

There is an inverse relationship between lust and attachment. It is dose dependent (e.g., increasing testosterone can decrease vasopressin and oxytocin, increasing vasopressin can decrease testosterone, increasing oxytocin in both males and females can decrease the impact of dopamine and norepinephrine). (Fisher, Helen, PhD. The First Sex. p 90-100. NY:Random House, 1999.)