Phentermine?

Phentermine is a stimulant, a controlled substance, narcotic, in the family of amphetamines AKA "speed". You cannot take phentermine long term. As soon as you stop taking it the weight you lost will slowly start to return.

This came from LiveStrong.com

"The drug Phentermine is part of an overall weight-loss program that includes dieting, exercising and counseling. It suppresses the appetite by increasing the metabolic rate and blood pressure. Dr. Sunny E. Ohia has done extensive research on its use, side effects and what happens to the human body when it's taken. It is only to be prescribed for eight to 12 weeks. By that time, the effects of it will be gone; increasing the dosage only causes dependency and an increase in dangerous side effects that are already associated with this drug. Discontinued use of Phentermine causes dizziness, depression and fatigue.
Most Dangerous Side Effects

Dr. Ohia points out that besides addiction, the most serious side effects of Phentermine are heart palpitations, tachycardia, arrhythmia, high blood pressure, low blood pressure and pulmonary hypertension. Heart palpitations are noticeable irregularities in the heartbeat. They may be too slow, too fast or irregular. Tachycardia is a rapid heartbeat of more than 100 beats a minute. Arrhythmia is a skipping, rapid or pounding heartbeat. Pulmonary hypertension is high blood pressure specifically in the pulmonary artery, vein or capillaries, which are those related to the lungs. It was these side effects, particularly pulmonary hypertension, that caused sudden death for several users, which resulted in the recall of Phentermine.

Additional and Pre-existing Side Effects

Phentermine also causes dry mouth, unpleasant taste, nausea, vomiting, abdominal discomfort, diarrhea and constipation. These side effects happen in the digestive system, indicating the body is rejecting something it's being given to digest. Change in the libido or sex drive may also occur. A person who has anxiety, a history of drug abuse, nervousness, restlessness, dizziness, insomnia, euphoria, depression, agitation or headaches is in danger, as these are additional side effects of Phentermine or its discontinuation. If a person has psychological problems, seizures, low blood sugar, hyperthyroidism, glaucoma or is sensitive to tartrazene, he is medically advised to be reluctant to take Phentermine. MAO inhibitors cause drug interaction, even if they haven't been taken up to 14 days prior.
Medical History and Phentermine
In addition to the effects on the human body that have been described, Phentermine is even more dangerous to the person with heart disease and high blood pressure. Because the most serious side effects include heart malfunction and high blood pressure, Phentermine would obviously maximize the effects of these health problems. If a person is taking another drug that stimulates the nervous system, there is a medical alert against the taking of Phentermine, which stimulates the nervous system as well. This will cause overstimulation, which is an exaggerated reaction to what one sees, hears, touches, tastes and smells. It can also be expressed in the form of hyperactivity or the inability to be normal or calm in activity."