Before taking phentermine,tell your doctor and pharmacist if you are allergic to phentermine, any other medications, or any of the ingredients in phentermine tablets. Ask your pharmacist for a list of the ingredients.tell your doctor or pharmacist if you are taking the following medications or have stopped taking them within the past two weeks: monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan®), phenelzine (Nardil®), selegiline (Eldepryl®, Emsam®, Zelapar®) and tranylcypromine (Parnate®).some medications should not be taken with phentermine. Other medications may cause dosing changes or extra monitoring when taken with phentermine. Make sure you have discussed any medications you are currently taking or plan to take before taking phentermine with your doctor and pharmacist. Before starting, stopping, or changing any medications while taking phentermine, please get the advice of your doctor or pharmacist.tell your doctor if you have or have ever had heart disease, high blood pressure, arteriosclerosis (narrowing of the arteries), hyperthyroidism (overactive thyroid gland), diabetes, glaucoma, or a history of drug abuse.tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking phentermine, call your doctor.talk to your doctor about the risks and benefits of taking phentermine if you are 65 years of age or older. Older adults should not usually take phentermine because it is not as safe as other medications that can be used to treat the same condition.you should know that this medication may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.ask your doctor about the safe use of alcohol while you are taking phentermine. Alcohol can make the side effects of phentermine worse.if you have diabetes, you may need to decrease your dose of insulin while taking phentermine. Call your doctor if you have questions or problems.What special dietary instructions should I follow?, Phentermine is an appetite suppressant used together with diet and exercise to treat obesity. Learn about side effects, interactions and indications., Phentermine works as an appetite suppressant and can help people lose weight in combination with diet and exercise. But the medication may not be safe for certain people..