"I care about the levels of hormones that are circulating my body because I know it affects my brain," said Casten.
A study in the New England Journal of Medicine finds IUDs or intrauterine devices and hormonal implants are 20 times more effective at preventing pregnancies than short term contraceptives like birth control pills, the patch or the ring.
"There's a one time placement and doesn't require a daily administration, weekly or monthly administration," said Dr. Adam Jacobs.
There are two kinds of IUDs . Both are inserted in the uterus -- the hormonal IUD is approved for five years. The copper IUD up to 10 years. Hormonal implants which go in the upper arm can last for three years.
IUDs and implants have the lowest failure rate, but they're not very popular. A big reason: Many women cannot afford the up front costs, which can be more than 500 dollars.
The study showed that when IUDs were offered for free, 75 percent of women chose them.
Older IUDs were linked to pelvic inflammatory disease but doctors say current ones are very safe.
"Women clearly are not at increased risk of infection and are also not at risk of having problems getting pregnant in the future after getting the IUD removed," said Dr. Jacobs.
Medical student Casten likes the convenience.
"I don't have to worry about getting my pills every three month. I really don't have to think about it at all," said Casten.
And she won't have to think about it for another four years.
About three million pregnancies in the United States are unplanned every year. Past studies have shown that about half of these pregnancies are the result of contraception failure.