fetal brain development and pregnancy outcomes. There is also risk of stillbirth and pre-term birth. Nicotine use will probably harm fetal neurological development. Risks to the child later in life from nicotine exposure during pregnancy include type 2 diabetes, obesity, hypertension, neurobehavioral defects, respiratory dysfunction, and infertility. Nicotine exposure during pregnancy can result in attention deficit hyperactivity disorder (ADHD) and learning disabilities in the child. It also puts the child at increased risk for nicotine addiction in the future. Pregnant women should consider behavioral therapy before NRT is considered. Youth In people under the age of eighteen, a physician is often consulted before starting NRT. The evidence suggests that exposure to nicotine between the ages of 10 and 25 years causes lasting harm to the brain and cognitive ability. Evidence is unclear whether adolescents gain benefit from cognitive-behavioral therapy or smoking cessation over the long-term as of 2017. Most tobacco users are under-eighteens when they start, and almost no-one over the age of 25 starts using. Cardiovascular conditions While there is no evidence that NRT can increase the risk of heart attacks, individuals with pre-existing cardiovascular conditions or recent heart attacks should consult a physician before initiating NRT. Smoking is known to cause cardiovascular diseases such as coronary heart disease, hypertension, heart attack, stroke, and peripheral artery disease. Cigarette smoking is the cause of 20% of all cardiovascular deaths in the United States, which is the leading cause of mortality. Other conditions Nicotine replacement therapies should be used cautiously in individuals with the following conditions: severe reactive airway diseases (for nasal spray), chronic nasal disorders such as sinusitis, polyps, rhinitis, or allergy (for nasal spray), diabetes (insulin-dependent), gastrointestinal diseases such as esophagitis, active gastric or peptic ulcer disease, liver problems, hyperthyroidism,pheochromocytoma, phenylketonuria (for lozenges), renal problems, and skin conditions such as psoriasis or dermatitis (for the transdermal patch). Mechanism of action Nicotine replacement therapy works by reducing cravings due to nicotine addiction. Smoking cigarettes releases high doses of nicotine to the brain in a matter of seconds as opposed to low doses released over a period of minutes to hours by the various forms of nicotine replacement therapy. Nicotine from NRT does not reach as high a concentration in the blood as does nicotine from smoke inhalation due to different absorption methods. NRT relies on systemic venous absorption, whereas nicotine from cigarettes reaches the arterial system. Nicotine replacement products vary