What the label lists and what reports show
Phentermine and topiramate side effects
Phentermine and topiramate's FDA label: “Most common adverse reactions in: Adults (incidence ≥ 5% and at least 1.5 times placebo) are: paraesthesia, dizziness, dysgeusia, insomnia, constipation, and dry mouth ( 6.1 ).” FAERS holds 5,790 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is headache (362 reports).
- Generic listed
- DEA Schedule IV
Check it at the source: the phentermine and topiramate FDA label on DailyMed (effective April 22, 2026); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of QSYMIA?QSYMIA can cause serious side effects, including: See " What is the most important information I should know about QSYMIA? " Mood changes and trouble sleeping. QSYMIA may cause depression or mood problems, and trouble sleeping. Tell your health care provider if symptoms occur. Concentration, memory, and speech difficulties. QSYMIA may affect how you think and cause confusion, problems with concentration, attention, memory, or speech. Tell your health care provider if symptoms occur. Slowing of growth. QSYMIA may slow the increase in height in children 12 years and older, when used for a long time. Increases of acid in bloodstream (metabolic acidosis). If left untreated, metabolic acidosis can cause brittle or soft bones (osteoporosis, osteomalacia (rickets), osteopenia), kidney stones, can slow the rate of growth in children, and may possibly harm your baby if you are pregnant. […]
Source: FDA drug label, Vivus LLC, effective April 22, 2026 (SPL set 40dd5602-53da-45ac-bb4b-15789aba40f9), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions in: Adults (incidence ≥ 5% and at least 1.5 times placebo) are: paraesthesia, dizziness, dysgeusia, insomnia, constipation, and dry mouth ( 6.1 ).
Table 1. Adverse Reactions Reported in ≥2% of QSYMIA-Treated Adults with Overweight or Obesity and More Frequently than Placebo in Overall Study Population of 1 Year Duration
| Adverse Reaction | Placebo (N = 1561) % | QSYMIA 3.75 mg/23 mg (N = 240) % | QSYMIA 7.5 mg/46 mg (N = 498) % | QSYMIA 15 mg/92 mg (N = 1,580) % |
|---|---|---|---|---|
| Paraesthesia | 2 | 4 | 14 | 20 |
| Dry Mouth | 3 | 7 | 14 | 19 |
| Constipation | 6 | 8 | 15 | 16 |
| Upper Respiratory Tract Infection | 13 | 16 | 12 | 14 |
| Headache | 9 | 10 | 7 | 11 |
| Dysgeusia | 1 | 1 | 7 | 9 |
| Insomnia | 5 | 5 | 6 | 9 |
| Nasopharyngitis | 8 | 13 | 11 | 9 |
| Dizziness | 3 | 3 | 7 | 9 |
| Sinusitis | 6 | 8 | 7 | 8 |
| Nausea | 4 | 6 | 4 | 7 |
| Back Pain | 5 | 5 | 6 | 7 |
| Fatigue | 4 | 5 | 4 | 6 |
| Diarrhea | 5 | 5 | 6 | 6 |
| Vision Blurred | 4 | 6 | 4 | 5 |
| Bronchitis | 4 | 7 | 4 | 5 |
| Urinary Tract Infection | 4 | 3 | 5 | 5 |
| Cough | 4 | 3 | 4 | 5 |
| Influenza | 4 | 8 | 5 | 4 |
| Depression | 2 | 3 | 3 | 4 |
| Anxiety | 2 | 3 | 2 | 4 |
| Hypoesthesia | 1 | 1 | 4 | 4 |
| Irritability | 1 | 2 | 3 | 4 |
| Alopecia | 1 | 2 | 3 | 4 |
| Disturbance in Attention | 1 | 0 | 2 | 4 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: Embryo-Fetal Toxicity [see Warnings and Precautions (5.1) and Use in Specific Populations (8.1 , 8.6) ] Suicidal Behavior and Ideation [see Warnings and Precautions (5.2) ] Risk of Ophthalmologic Adverse Reactions [see Warnings and Precautions (5.3) ] Mood and Sleep Disorders [see Warnings and Precautions (5.4) ] Cognitive Impairment [see Warnings and Precautions (5.5) ] Slowing of Linear Growth [see Warnings and Precautions (5.6) ] Metabolic Acidosis [see Warnings and Precautions (5.7) ] Decrease in Renal Function [see Warnings and Precautions (5.8) ] Risk of Seizures with Abrupt Withdrawal of QSYMIA [see Warnings and Precautions (5.9) ] Kidney Stones [see Warnings and Precautions (5.10) ] Oligohydrosis and Hyperthermia [see Warnings and Precautions (5.11) ] Hypokalemia [see Warnings and Precautions (5.12) ] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity Reactions [ see Warnings and Precautions (5.13) ] Serious Skin Reactions [see Warnings and Precautions (5.14) ] Anaphylaxis and Angioedema [see Warnings and Precautions (5.15) ] Allergic Reactions Due to Inactive Ingredient FD&C Yellow No. …
Source: FDA drug label, Vivus LLC, effective April 22, 2026 (SPL set 40dd5602-53da-45ac-bb4b-15789aba40f9), via openFDA; the full label on DailyMed
What do FAERS reports show?
5,790 reports list phentermine and topiramate among the medicines taken, each a report of something that happened, not proof the medicine caused it; 16 are coded as a death and 221 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Reports rose sharply in 2025 (1,186, against a median of 271 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 23 reactions below, 14 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Phentermine and topiramate: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions