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Created Feb 2019 | Updated Nov 2020


  • [DIDREX]

DEA CODE 1228: Schedule 3

Benzphetamine is a sympathomimetic agent with properties similar to dextroamphetamine. It is used in the management of exogenous obesity as a short term (a few weeks) adjunct in a regimen of weight reduction based on caloric restriction in patients with an initial body mass index (BMI) of 30 kg/m2 or higher who have not responded to appropriate weight reducing regimen (diet and/or exercise) alone. Presumably, benzphetamine produces its effects through mechanisms similar to amphetamine via induces synaptic vesicular amine transporter, but precise mechanism of action of benzphetamine is not known.

Weight Loss drug:
Didrex is the brand name for the generic drug benzphetamine. It is a sympathomimetic amine and is similar in make up to amphetamines. Didrex is used as a short-term supplement to diet and exercise in the treatment of obesity. Didrex works to stimulate the central nervous system, thereby increasing the heart rate and blood pressure and decreasing appetite. In the use of Didrex, a patient can put themselves at risk as health care professionals often warn that the use of diet pills is one of the most dangerous methods for losing weight. The use of Didrex or its derivatives should only be applied under the close care of a doctor.

Its chemical and pharmacological similarity to amphetamines and related stimulant drugs. Didrex is dangerously addictive and the possibility of abuse must be seriously considered before it is selected as part of a weight reduction program. The abuse of Didrex, amphetamines and other related drugs is thought to be associated with the intense psychological dependence and severe social dysfunction. Patients have reported using more of the medication than has been prescribed in order to achieve a desired effect. Such use and abuse builds a tolerance to Didrex, which can lead to a psychological and physiological dependence.

Important Information:

Benzphetamine can harm an unborn baby or cause birth defects. Do not use benzphetamine if you are pregnant.

Do not use benzphetamine 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.

Taking benzphetamine together with other diet medications (including medicines available over the counter) can cause a rare fatal lung disorder called pulmonary hypertension. Do not take benzphetamine with any other diet medications without your doctor's advice.

Benzphetamine may be habit-forming and should be used only by the person it was prescribed for.

Never share benzphetamine with another person, especially someone with a history of drug abuse or addiction.

Keep track of the amount of medicine used from each new bottle. Benzphetamine is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

Drinking alcohol can increase certain side effects of benzphetamine.

To prevent sleep problems, avoid taking this medication late in the afternoon.

Benzphetamine may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.


Drug Interactions (201) Alcohol/Food Interactions (3) Disease Interactions (17)

What other drugs will affect Benzphetamine?
Tell your doctor about all medicines you use, and those you start or stop using during your treatment with benzphetamine, especially:
  • an antidepressant - citalopram, escitalopram, desvenlafaxine, duloxetine, fluoxetine, paroxetine, sertraline, venlafaxine, vilazodone, and others
  • a stimulant or ADHD medication such as Adderall or Ritalin
This list is not complete. Other drugs may interact with benzphetamine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

A total of 201 drugs are known to interact with Benzphetamine.

  • 43 major drug interactions
  • 153 moderate drug interactions
  • 5 minor drug interactions

Benzphetamine hydrochloride is sold as Didrex, an FDA-approved drug for people who struggle with obesity. Benzphetamine is monitored under the Controlled Substance act since it can put users at a serious risk for abuse and addiction. Because of its chemical and pharmacological relation to amphetamines, the FDA warns about the possibility of becoming addicted to the stimulant. Negative side effects include cardiovascular palpitation, elevated blood pressure, and gastrointestinal issues. Over stimulation, insomnia, and tremor have also been reported, and in rare cases, psychotic episodes have occurred Withdrawal can also be a problem, sometimes leading to depression. Even if you get a prescription for Didrex, it can put your health at serious risk.

Didrex (benzphetamine)
Side Effects:
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Stop using benzphetamine and call your doctor at once if you have
  • shortness of breath (even with mild exertion), swelling, rapid weight gain
  • chest pain, feeling like you might pass out
  • pounding heartbeats or fluttering in your chest
  • confusion or irritability, unusual thoughts or behavior
  • dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, confusion, chest pain, shortness of breath, uneven heartbeats, seizure)
Common side effects may include:
  • feeling restless or hyperactive
  • headache, dizziness, tremors
  • sleep problems (insomnia)
  • increased sweating
  • dry mouth or an unpleasant taste in your mouth
  • nausea, diarrhea upset stomach
  • skin rash
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Appropriate studies have not been performed on the relationship of age to the effects of benzphetamine in children.

Use of this medicine is not recommended in children younger than 17 years of age.

Appropriate studies have not been performed on the relationship of age to the effects of benzphetamine in the elderly. However, elderly patients are more likely to have age-related liver, kidney, or heart problems, which may require caution and an adjustment in the dose for patients receiving benzphetamine.

Other Medical Problems:
Make sure you tell your doctor if you have any other medical problems, especially:

  • Agitation or anxiety, severe
  • Drug abuse or dependence, history of
  • Glaucoma
  • Heart or blood vessel disease
  • Heart rhythm problems
  • High blood pressure, moderate or severe
  • Overactive thyroid - Should not be used in patients with these conditions
  • Diabetes
  • High blood pressure, mild
  • Lung or breathing problems
  • Mental illness - Use with caution. This medicine may make these conditions worse

Benzphetamine Hydrochloride
Maximum Dosage:
Prescribers Digital Reference
Adults:150 mg/day PO.
Elderly150 mg/day PO.
Adolescents:150 mg/day PO.
Children:Safety and efficacy have not been established.

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