What You Should Know About Benzphetamine Side Effects

Starting a new medication can be nerve-racking, especially when it's a controlled substance like Benzphetamine. Knowing what side effects to expect — and which ones are red flags — can help you feel more prepared and in control.

This guide covers the most common side effects, the serious ones to watch for, and practical tips for managing them.

What Is Benzphetamine?

Benzphetamine (brand names Didrex and Regimex) is a Schedule III prescription appetite suppressant approved for short-term weight loss in adults with a BMI of 30 or higher. It works by stimulating the central nervous system to reduce hunger. For a deeper look at how the medication works, see our guide on Benzphetamine's mechanism of action.

Like all medications, Benzphetamine can cause side effects. Most are mild and go away as your body adjusts, but some require medical attention.

Common Side Effects

These side effects are reported most often. They're usually mild and tend to improve within the first week or two of treatment:

• Dry mouth — One of the most frequently reported effects. Sipping water throughout the day and chewing sugar-free gum can help.
• Insomnia or trouble sleeping — Benzphetamine is a stimulant, so it can keep you awake. Taking your dose in the mid-morning or mid-afternoon (not late in the day) helps prevent this.
• Restlessness and irritability — You may feel jittery or on edge, especially when you first start.
• Dizziness — Usually mild. Stand up slowly from sitting or lying positions.
• Headache — Often temporary. Over-the-counter pain relievers can help if needed.
• Nausea — May improve if you take the medication with a small snack.
• Constipation or diarrhea — Digestive changes are common with appetite suppressants. Staying hydrated and eating fiber-rich foods can help.
• Tremor — Slight shaking, especially in the hands.
• Increased sweating — Your body may sweat more than usual.
• Unpleasant taste — Some patients notice a metallic or odd taste in their mouth.

Serious Side Effects — When to Call Your Doctor

While rare, some side effects are serious and need immediate medical attention. Contact your doctor right away if you experience any of the following:

• Rapid or irregular heartbeat (palpitations/tachycardia) — A pounding or racing heart can signal cardiovascular stress. Do not ignore this.
• Significant increase in blood pressure — Symptoms may include severe headache, blurred vision, or chest tightness. If you monitor your blood pressure at home, report any readings that are consistently elevated.
• Chest pain or shortness of breath — Could indicate a serious cardiac or pulmonary issue. Seek emergency care.
• Psychotic episodes — In rare cases, stimulant medications can cause hallucinations, paranoia, or severely disordered thinking. This is a medical emergency.
• Seizures — Rare but serious. Call 911 immediately.
• Signs of dependence or withdrawal — If you feel you need to take more than prescribed, or experience depression and extreme fatigue when stopping, talk to your doctor. Benzphetamine has abuse potential, which is why it's classified as Schedule III.

Rare but reported with similar medications: Pulmonary hypertension (high blood pressure in the lungs) and valvular heart disease have been associated with anorectic medications as a class. While these have not been specifically linked to Benzphetamine alone, they are worth knowing about.

Special Populations

Some groups need extra caution with Benzphetamine:

Pregnant and Breastfeeding Women

Benzphetamine is contraindicated in pregnancy — it can cause harm to a developing baby. It is also not recommended during breastfeeding. If you become pregnant while taking Benzphetamine, stop the medication and contact your doctor immediately.

Patients Under 17

Benzphetamine is not recommended for patients under 17 years of age. Safety and effectiveness have not been established in this age group.

Elderly Patients

Older adults should use Benzphetamine with caution. Age-related changes in heart function, blood pressure, and kidney or liver function may increase the risk of side effects.

People With Certain Medical Conditions

Benzphetamine should not be used by anyone with:

• Advanced arteriosclerosis or symptomatic cardiovascular disease
• Moderate to severe hypertension
• Hyperthyroidism
• Glaucoma
• A history of drug abuse
• Agitated states

If you have any of these conditions, your doctor should explore alternative weight loss options with you.

Managing Side Effects

Here are some practical strategies to minimize common side effects:

Timing Your Dose

Take Benzphetamine in the mid-morning or mid-afternoon — not late in the day. This matches how your body processes the medication and reduces the chance of insomnia.

Staying Hydrated

Drink plenty of water throughout the day. This helps with dry mouth, constipation, and headaches.

Eating Regularly

Even though Benzphetamine suppresses appetite, try to eat balanced meals. Skipping meals can worsen dizziness, headaches, and irritability.

Tracking Your Symptoms

Keep a simple log of any side effects you notice — what happened, when, and how severe. This gives your doctor useful information at your follow-up visits.

Communicating With Your Doctor

Don't wait until your next scheduled appointment if something feels off. Call your doctor's office if a side effect is bothering you or getting worse. They may adjust your dose or suggest a different medication.

What About Drug Interactions?

Some side effects can be made worse by interactions with other medications. Benzphetamine has serious interactions with MAO inhibitors, other stimulants, and several other drug classes. Read our full guide on Benzphetamine drug interactions to learn what to avoid.

Final Thoughts

Most people who take Benzphetamine experience only mild side effects that go away on their own. Dry mouth, trouble sleeping, and restlessness are the most common complaints. Serious side effects are rare but real — knowing the warning signs helps you act quickly if something goes wrong.

The best thing you can do is stay in close contact with your prescriber, especially during the first few weeks. And if you're still looking for a provider, check out our guide on how to find a doctor who prescribes Benzphetamine.