Phentermine (also known as Adipex, Suprenza, and Lomaira) is the oldest and most widely used weight loss medication. It was originally used as a short-term medication to jump-start weight loss, but now newer medical guidelines have added it to long-term therapy. Some patients may lose about 5% of their body weight by taking phentermine.

In the US, phentermine is almost exclusively available in the HCl formulation – available in 15 mg and 30 mg strength. Side effects include headache, overstimulation, high blood pressure, insomnia, rapid or irregular heart rate, and tremor.

Interactions may occur during or within 14 days following the use of monoamine oxidase (MAO) inhibitors, sympathomimetics, alcohol, adrenergic neuron-blocking drugs, and possibly some anesthetic agents.

Qsymia is the combination of Phentermine and Topiramate to decrease appetite and cravings. Having the combination of two drugs increases efficacy.

Adults with migraines and obesity are good candidates for this weight-loss medication. Some patients may lose an average of 5–10% of body weight.

If more than 5% weight loss is not achieved after 12 weeks of the maximum dose, the weight loss pill should be gradually discontinued.

Daily doses with four strengths start at 3.75 mg/23 mg to 15 mg/92 mg. Side effects include abnormal sensations, dizziness, altered taste, insomnia, constipation, and dry mouth. Contraindications include uncontrolled hypertension and coronary artery disease, hyperthyroidism, glaucoma, and sensitivity to stimulants.