A review.The advantages of a non-invasive method of drug delivery that offers both convenience and efficiency already outweigh the more traditional methods of oral delivery and hypodermic needles as the process eliminates gastrointestinal toxicity and first-pass metabolism associated with the more conventional techniques.Fentanyl, 2 anti-parkinson drugs, a bladder incontinence drug, and nitroglycerin transdermal solutions have been approved by the FDA.