How to use Phentermine HCL

Take this medication by mouth as directed by your doctor, usually once a day, 1 hour before breakfast or 1 to 2 hours after breakfast. If needed, your doctor may adjust your dose to take a small dose up to 3 times a day. Carefully follow your doctor’s instructions. Taking this medication late in the day may cause trouble sleeping (insomnia).

If you are using sustained-release capsules, the dose is usually taken once a day before breakfast or at least 10 to 14 hours before bedtime. Swallow the medication whole. Do not crush or chew sustained-release capsules. Doing so can release all of the drug at once, increasing the risk of side effects.

If you are using the tablets made to dissolve in the mouth, the dose is usually taken once a day in the morning, with or without food. First, dry your hands before handling the tablet. Place your dose on top of the tongue until it dissolves, then swallow it with or without water.

The dosage is based on your medical condition and response to therapy. Your doctor will adjust the dose to find the best dose for you. Use this medication regularly and exactly as prescribed in order to get the most benefit from it. To help you remember, take it at the same time(s) each day.

This medication is usually taken for only a few weeks at a time. It should not be taken with other appetite suppressants (see also Drug Interactions section). The possibility of serious side effects increases with longer use of this medication and use of this drug along with certain other diet drugs.

Before taking this medicine

You should not use phentermine if you are allergic to it, or if you have:

• a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, stroke);
• severe or uncontrolled high blood pressure;
• overactive thyroid;
• glaucoma;
• extreme agitation or nervousness;
• a history of drug abuse; or
• if you take other diet pills.

Do not use phentermine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.

If you suddenly stop using this medication, you may have withdrawal symptoms (such as depression, severe tiredness). To help prevent withdrawal, your doctor may lower your dose slowly. Withdrawal is more likely if you have used phentermine for a long time or in high doses. Tell your doctor or pharmacist right away if you have withdrawal.

Though it helps many people, this medication may sometimes cause addiction. This risk may be higher if you have a substance use disorder (such as overuse of or addiction to drugs/alcohol). Do not increase your dose, take it more often, or use it for a longer time than prescribed. Properly stop the medication when so directed.

This medication may stop working well after you have been taking it for a few weeks. Talk with your doctor if this medication stops working well. Do not increase the dose unless directed by your doctor. Your doctor may direct you to stop taking this medication.

Phentermine side effects

Get emergency medical help if you have signs of an allergic reaction to phentermine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• feeling short of breath, even with mild exertion;
• chest pain, feeling like you might pass out;
• swelling in your ankles or feet;
• pounding heartbeats or fluttering in your chest;
• tremors, feeling restless, trouble sleeping;
• unusual changes in mood or behavior; or
• increased blood pressure – severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.

Common phentermine side effects may include:

• itching;
• dizziness, headache;
• dry mouth, unpleasant taste;
• diarrhea, constipation, stomach pain; or
• increased or decreased interest in sex.