Do not take this medication if you are pregnant or breast-feeding a baby. You should also avoid using it in case you have glaucoma, overactive thyroid disease such as hyperthyroidism and thyrotoxicosis; severe heart problems like myocardial infarction within the last three months before taking medicines prescribed for ADHD (such as atomoxetine). Additionally patients with uncontrolled high blood pressure shouldn't use phentermine either since these will aggravate their condition when taken together.