Dry mouth, sleep problems, dizziness, heart palpitations, skin flushing, fatigue, constipation, irritability, nausea, and vomiting are the most commonly reported side effects of phentermine and combined phentermine and topiramate.
While severe side effects are relatively rare, they include elevated blood pressure, suicidal ideation, metabolic acidosis, increased creatinine levels, fetal harm, vision problems, cognitive impairment, and hypokalemia.