Qsymia Side Effects: What to Expect and When to Call Your Doctor

Qsymia (phentermine/topiramate extended-release) is effective for weight management, but like any medication, it comes with a side effect profile worth understanding before you start. Knowing what's normal, what's manageable, and what requires a call to your doctor can make your experience with Qsymia safer and less stressful.

Most Common Side Effects of Qsymia

In controlled clinical trials in adults, the following side effects occurred in at least 5% of Qsymia patients and at least 1.5 times more frequently than in placebo patients:

Paresthesia ("pins and needles"): A tingling or numbness sensation in the hands, feet, or face. This is the most commonly reported side effect of Qsymia. It's caused by topiramate's effect on carbonic anhydrase and is usually mild and temporary.

Dizziness: Lightheadedness, especially when standing up quickly. Often improves after the first few weeks.

Dysgeusia (altered taste): Food may taste different or less appealing than usual. This can actually support weight loss by reducing the pleasure of eating.

Insomnia: Difficulty sleeping, especially if Qsymia is taken late in the day. Always take Qsymia in the morning to minimize sleep disruption.

Constipation: Reduced bowel frequency is common. Increasing water and fiber intake typically helps.

Dry mouth: A frequent complaint that usually improves over time. Staying well-hydrated helps.

Side Effects in Adolescents (Ages 12–17)

In clinical trials for pediatric patients aged 12–17, the most commonly reported side effects (occurring in at least 4% of patients and more than placebo) were:

Depression

Dizziness

Joint pain (arthralgia)

Fever (pyrexia)

Flu-like symptoms (influenza)

Importantly, Qsymia may slow height growth in adolescents. Pediatric prescribers should monitor height velocity throughout treatment.

Serious Side Effects: When to Call Your Doctor Immediately

Some Qsymia side effects are serious and require prompt medical attention:

Eye pain or vision changes: Stop Qsymia and seek care immediately if you develop sudden eye pain, redness, or vision changes. Topiramate can cause acute myopia and secondary angle-closure glaucoma.

Suicidal thoughts or behavior: Topiramate carries a risk of suicidal thoughts, especially in the first weeks of treatment. Call 911 or go to an emergency room immediately. If not in crisis, call the 988 Suicide and Crisis Lifeline.

Severe mood changes or depression: Contact your doctor if you notice worsening depression, unusual mood swings, or significant behavioral changes.

Decreased sweating + overheating: Topiramate can reduce sweating (oligohidrosis), raising the risk of heat-related illness. If you notice you're not sweating normally during exercise in hot weather, take it seriously and contact your provider.

Kidney stones: Topiramate can increase kidney stone risk by inhibiting carbonic anhydrase. Symptoms include sudden back or flank pain, blood in urine, and painful urination.

Fast or irregular heartbeat: Phentermine can increase heart rate. Significant palpitations or an irregular heartbeat should be reported to your doctor.

Severe skin reactions: If you develop a rash, blistering, or peeling skin, stop Qsymia and seek medical attention. Stevens-Johnson syndrome has been reported rarely with topiramate use.

Boxed Warnings: Fetal Harm

Qsymia carries a boxed warning for fetal harm. Topiramate can cause cleft lip and/or cleft palate and small-for-gestational-age outcomes if taken during pregnancy, especially in the first trimester. If you become pregnant while taking Qsymia, stop the medication immediately and contact your healthcare provider and the Qsymia Pregnancy Surveillance Program at 1-888-998-4887.

Important Safety Note: Do Not Stop Abruptly

Do not stop the highest dose of Qsymia (15/92 mg) abruptly. The topiramate component can lower the seizure threshold if stopped suddenly. Taper by taking 15/92 mg every other day for at least one week before discontinuing completely.

For a complete guide on Qsymia drug interactions, see our article Qsymia Drug Interactions: What to Avoid and What to Tell Your Doctor. For tips on finding Qsymia in stock, visit medfinder.com.