Contraceptive patch
A contraceptive patch is a transdermal patch applied to the skin that releases synthetic estrogen and progestin hormones to prevent pregnancy. They are thought to have the same effectiveness as the combined oral contraceptive pill.
The only currently available contraceptive patches are Ortho Evra, marketed in the United States by Ortho-McNeil, and Evra marketed in Canada by Janssen-Ortho and marketed in the United Kingdom and other countries by Janssen-Cilag. The patches are packaged in boxes of three and are only available by prescription. The contraceptive patch is often informally referred to as "the Patch".

# Method of use
A woman applies her first patch onto her upper outer arm, buttocks, abdomen or thigh on either the first day of her menstrual cycle (day 1) or on the first Sunday following that day, whichever she prefers. The day of application is known from that point as patch change day.  Seven days later, when patch change day comes again, the woman removes the patch and applies another to one of the approved locations on the body.  This process is repeated again on the next patch change day.  On the following patch change day, the patch is removed and not replaced.  The woman waits 7 days without a patch in place, and on the next patch change day she applies a new patch.

## Backup contraception
- If a woman chooses to begin with her patch change day as day 1 of her menstrual cycle, the patch is able to take effect in time to prevent ovulation (see Mechanism of Action below) and no form of backup contraception is needed at all.
In the case that a woman wishes to begin using the contraceptive patch following a first trimester abortion or miscarriage, patch application can be done immediately afterwards.  This can be considered the same as a day 1 start above, and no backup contraception is required.
- In the case that a woman wishes to begin using the contraceptive patch following a first trimester abortion or miscarriage, patch application can be done immediately afterwards.  This can be considered the same as a day 1 start above, and no backup contraception is required.
- If a woman chooses to begin with her patch change day as the first Sunday following day 1, it is necessary to use a backup form of contraception such as spermicide or condoms for the first week of patch wear.

# Mechanism of action
Like all combined hormonal contraceptives, Ortho Evra / Evra works primarily by preventing ovulation. A secondary mechanism of action is inhibition of sperm penetration by changes in the cervical mucus. Hormonal contraceptives also have effects on the endometrium that theoretically could affect implantation, however no scientific evidence indicates that prevention of implantation actually results from their use.
The 20 cm2 Ortho Evra contraceptive patch contains 750 g ethinyl estradiol (an estrogen) and 6000 g norelgestromin (a progestin). 
The 20 cm2 Evra contraceptive patch contains 600 g ethinyl estradiol and 6000 g norelgestromin. 
The Ortho Evra contraceptive patch and the Evra contraceptive patch are both intended to gradually release into the systemic circulation approximately 20 g/day of ethinyl estradiol and 150 g/day of norelgestromin.

# Interactions and Contraindications
Contraceptive effectiveness of the patch or any other hormonal contraceptive may be reduced significantly if co-administered alongside various antibiotics, antifungals, anticonvulsants, or other drugs that increase metabolism of contraceptive steroids.
However, despite the interactions with many other antibiotics, a clinical pharamacokinetic drug interaction study showed that oral administration of tetracycline HCl 500 mg for 3 days prior to and 7 days during use of Ortho Evra did not reduce effectiveness of Ortho Evra.  This is a significant factor in the common decision to administer tetracycline-derived antibiotics following an abortion (preventatively to fight potential infection) when synthetic hormone contraceptives are to be used afterwards.
Drugs containing St. John's Wort are also known to affect the effectiveness of hormonal contraceptives.

# Side effects
In three large clinical trials involving a total of 3,330 women using the Ortho Evra / Evra patch for up to one year, 12% of users discontinued the patch because of adverse events. The most frequent adverse events leading to patch discontinuation were: nausea and/or vomiting (2.4%), application site reaction (1.9%), breast discomfort, engorgement or pain (1.9%), headache (1.1%), and emotional lability (1.0%).
The most frequent adverse events reported while using the Ortho Evra / Evra patch were: breast discomfort, engorgement or pain (22%), headache (21%), application site reaction (17%), nausea (17%), upper respiratory tract infection (10%), menstrual cramps (10%), and abdominal pain (9%).
Breakthrough bleeding and/or spotting while using the Ortho Evra / Evra patch was reported by: 18% in cycle 1, 12% in cycle 3, 8% in cycle 6 and cycle 13. Breakthrough bleeding (requiring more than one pad or tampon per day) was reported by: 4% in cycle 1, 3% in cycle 3 and cycle 6, and 1% in cycle 13.
Additional side effect information is provided in the Ortho Evra label information and the Evra SPC and PIL.

## Thromboembolic risks
All combined hormonal birth control products have a very small increased risk of serious or fatal thromboembolic events. Currently, there is ongoing research into the thromboembolic risks of Ortho Evra as compared to combined oral contraceptive pills. A recent study found that users of the contraceptive patch may have a twofold increased risk for non-fatal venous thromboembolic events compared with women who took a norgestimate-containing oral contraceptive with 35 g of estrogen. PMID 17267834   However, a different study published in the journal Contraception concludes that the risk of nonfatal venous thromboembolism for the contraceptive patch is similar to the risk for oral contraceptives containing 35 g of ethinyl estradiol and norgestimate (PDF file). The contradictory findings between the two studies is not easily resolved, because the confidence intervals for the studies are overlapping.
In 2004, the Associated Press reported that fatal adverse events were reported to the FDA for users of Ortho-Evra at three times the rate of fatal events in oral contraceptive users. .  However, these comparisons do not represent methodical scientific studies. The AP noted that, "Dr. Philip Darney, a professor of obstetrics and gynecology at the University of California, San Francisco, and a leading contraceptive researcher, cautioned that the FDAs adverse event reports tend to be inflated for newer products like the patch."
In studies with oral contraceptives, the risk for cardiovascular disease (such as thromboembolism) is significantly increased in women over the age of 35 years who also smoke tobacco (PMID 10818409).  Hence, Ortho-Evra's package insert states that "Women who use hormonal contraceptives, including ORTHO EVRA, should be strongly advised not to smoke". According to the manufacturer, the patches introduce a 60% higher level of estrogen into the bloodstream as compared to oral contraceptives; however, the clinical significance of this difference is unknown.
On November 10, 2005 Ortho McNeil, in conjunction with the FDA, revised the label for Ortho Evra, including a new bolded warning about higher exposure to estrogen for women using the weekly patch compared to taking a daily birth control pill containing 35 g of estrogen, noting that higher levels of estrogen may put some women at increased risk for getting blood clots.

# Lawsuits
The Patch has been associated with strokes and thrombosis and the mechanism for hormone absorption and dissipation from the body's tissues is different from "the pill". Several lawsuits have been instigated over these issues.
A lawsuit filed in Federal Court in New Jersey on September 2, 2005, by a Georgia woman, who suffered a pulmonary embolism, alleges the company promoted the patch despite knowledge of its health risks, for financial gain while failing to warn of the risks of blood clots and other injuries.
In November 2005, CBS News aired a story about documents that surfaced in a lawsuit involving a young mother who was paralyzed by a stroke and remained a total invalid, that showed the company had received nearly 500 reports of adverse events between April 2002 and December 2004. During the same time frame, only 61 adverse event reports were filed in connection with all type of birth control pills. 
The parents of a 14 year-old girl from Wisconsin have filed a lawsuit against Johnson & Johnson because they claim that she died from a blood clot that arose from her use of the patch.