Short answer: The phendimetrazine label lists side effects without percentages: palpitations, fast heartbeat, raised blood pressure, ischemic events, overstimulation, restlessness, insomnia, agitation, tremor, sweating, dizziness, headache, blurred vision, dry mouth, nausea, diarrhea, constipation, stomach pain and libido changes. Its warnings cover pulmonary hypertension, heart valve disease and tolerance. The label has no boxed warning.
What Phendimetrazine is approved for: Phendimetrazine is approved as a short-term (a few weeks) add-on to a calorie-restricted weight-loss plan for obesity in people with a starting BMI of 30 kg/m2 or more who have not responded to diet and/or exercise alone, and only on its own, not with other weight-loss drugs (Indications and Usage). The package label prints CIII, and the label calls it a controlled substance (Drug Abuse and Dependence).
Source
Phendimetrazine Tartrate Tablets, USP, 35 mg, CIII, prescribing information. Preferred Pharmaceuticals (repackager). DailyMed, version published August 17, 2026. DailyMed setid 767b5386-1e56-4eeb-8d59-510b940ab75e
No. The current Phendimetrazine label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Phendimetrazine.
| Body system | Reactions listed |
|---|---|
| Cardiovascular | Palpitations, tachycardia, elevated blood pressure, ischemic events. No case of valvulopathy has been reported when phendimetrazine tartrate has been used alone. |
| Central nervous system | Overstimulation, restlessness, insomnia, agitation, flushing, tremor, sweating, dizziness, headache, psychotic state, blurring of vision |
| Gastrointestinal | Dryness of the mouth, nausea, diarrhea, constipation, stomach pain |
| Genitourinary | Urinary frequency, dysuria, changes in libido |
In a case-control study, use of appetite-suppressant ("anorectic") drugs for longer than three months was linked to a 23-fold increase in the risk of pulmonary hypertension.
Tolerance to the appetite effect develops within a few weeks.
Stopping suddenly after long use of high doses leads to extreme fatigue and depression. Signs of chronic misuse include severe skin problems, marked insomnia, irritability, hyperactivity and personality changes; the most severe is psychosis.
Signs of overdose include unusual restlessness, confusion, belligerence, hallucinations and panic, followed by fatigue and depression, plus heart rhythm and blood pressure changes. Poisoning may result in convulsions, coma and death.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. People with allergy to stimulant amines, advanced hardening of the arteries, heart disease with symptoms, moderate or severe high blood pressure, an overactive thyroid or glaucoma; highly nervous or agitated people; people with a history of drug abuse; and people taking other stimulants, including MAO inhibitors.
Other weight-loss drugs. Phendimetrazine is not used with other appetite suppressants, including prescription, over-the-counter and herbal products.
Pulmonary hypertension. This rare, often fatal lung disease has been linked to appetite suppressants including phendimetrazine. New or worse shortness of breath on exertion, chest pain, fainting or leg swelling suggest it, and the drug is stopped right away.
Heart valve disease. Heart valve disease has been reported with some appetite suppressants, but no cases with phendimetrazine used alone. It is not recommended with a known heart murmur or valve disease, and a heart check before starting may be considered.
Continue only with early weight loss. Treatment is continued only with satisfactory weight loss in the first 4 weeks, for example at least 4 pounds. It is not recommended for people who used any appetite suppressant in the prior year.
Tolerance. Tolerance develops within a few weeks. When it does, the drug is stopped, and the maximum dose is not exceeded.
MAO inhibitors, driving and stopping. Use within 14 days of an MAO inhibitor may cause a blood pressure crisis. It may impair driving or operating machinery. Stopping suddenly after long high-dose use causes extreme fatigue and depression.
Blood pressure, diabetes and tartrazine. Caution is used even with mild high blood pressure. Insulin needs may change with diabetes. Only the yellow tablet contains FD&C Yellow No. 5 (tartrazine), which may cause allergic-type reactions in some people.
From the Warnings that comes with Phendimetrazine:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.