Take the immediate-release form of this medication by mouth as directed by your doctor, usually 2 to 3 times a day (1 hour before meals). Taking this medication late in the day may cause trouble sleeping (insomnia).

The sustained-release form of phendimetrazine is usually taken once a day 30 - 60 minutes before the morning meal. Swallow this medication whole. Do not crush, chew, or break the capsules. Doing so can destroy the long action of the drug and may increase side effects.

The dosage is based on your medical condition and response to treatment. 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.

Phendimetrazine 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.

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 phendimetrazine 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 while. 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.