Phentermine oral capsule doesn’t cause drowsiness, but it can cause trouble sleeping. It can also cause other side effects. More common side effects How does Adipex work? Phentermine HCl – the main ingredient in Adipex – is a sympathomimetic amine, which means it stimulates the nervous system. More specifically, it promotes the release of norepinephrine, which is a neurotransmitter (chemical in the brain) that evokes a stress response such as the “fight or flight” reaction and it. Adipex-P (phentermine) is an appetite suppressant used in combination with diet and exercise for the short-term treatment of obesity. A generic version of Adipex-P is available. If you experience any of the following more common side effects of phentermine and they don’t go away or become sever, call your doctor or seek emergency medical care: Detailed Orlistat dosage information for adults and children. Includes dosages for Obesity; plus renal, liver and dialysis adjustments. Phentermine is an appetite suppressant used together with diet and exercise to treat obesity. Learn about side effects, interactions and indications. Adderall (Adderall XR) is a prescription medication used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy in children and adults. Phentermine (Adipex-P and Lomaira) is a schedule IV controlled prescription drug used as a short-term weight loss in conjunction with diet and other lifestyle modifications to treat obesity. Side effects include impotence, hives, constipation, dry mouth, and nausea. Pregnancy and breastfeeding safety are provided. Discontinued brands include. Phentermine belongs to a class of drugs called “anorectics,” also known as appetite suppressants. Taking phentermine helps suppress your appetite, thereby limiting how many calories you eat. Phentermine supports weight loss by suppressing the appetite and boosting energy. On the most basic level, weight loss is a matter of creating an internal environment in which the body is expending energy in a manner that burns more calories than are being consumed.