For example, "They may choose someone they may not choose otherwise," he said. In theory, Roberts said a woman may choose a man while she's on the pill and feel fine, but subconsciously find her mate less attractive if she goes off the pill.
"There is evidence that couples that are more MCH similar to each other have more difficulty conceiving, and they have more miscarriages," added Roberts, who has also cited research that women who marry men with similar MCH genes are more likely to have an affair.
Aside from chemical conjectures, Einstein's Santoro has heard straight from her patients that the pill can affect one's sex life.
"Clearly, pills suppress androgen production in the ovary, so, to the extent that androgen levels drive sex drive in women, it could affect them," said Santoro, who is also a doctor with the Montefiore Medical Center in New York City.
"It's also possible for some women, especially if they're Catholics, to have a libido problem. ... Once they start on the pill, it may reduce their enjoyment in some way out of guilt," she said.
Santoro said many of her patients tend to think of the pill as an off-switch for hormones, but in truth, the pill exposes women to higher levels of hormones to overcome their own cycle.
"Because the pill in a lot of ways produces a pseudo-pregnant state, some of the side effects of pregnancy are noticed in the pill," Santoro said.
That means women on the pill may experience heartburn, or constipation, or sleep disturbances, either as insomnia or extra sleepiness.
Santoro said doctors are also less likely to get into great detail about weight changes.
"We tell our patients that weight doesn't change if you take the pill ... but among the individual women, there may be some who gain and some who lose," said Santoro, who added that large studies on the subject might cancel out the average weight changes experienced by women on the pill.
Overall, Santoro said she'd spend more time talking about the pill's more serious health risks and side effects with a patient.
"Women over 35 who smoke more than 10 cigarettes a day -- they shouldn't be taking the pill at all," she said.
For patients who have migraines with aura, which refers to feelings and symptoms noticed shortly before the headache begins, "they should not take pills without making sure everybody's on board."
Santoro said although research hasn't drawn any hard-and-fast conclusions about side effects from taking the pill for an extended period of time, many of her patients have decided to give the hormones a break.
"It's outdated, but some women feel better if they take a little 'pill holiday' now and then," she said.