Prescription medication · Sympathomimetic Amine (Appetite Suppressant)
phentermine
Also sold as Adipex-P, Lomaira. Phentermine is used for a few weeks to help with weight loss.
Data updated 2026-05-15
- 6,109
- FDA reportsLightly reported
- In shortage
- FDA status
What the data shows
phentermine (Adipex-P) is a prescription Sympathomimetic Amine (Appetite Suppressant), reported less often than most tracked drugs (6,109 FDA reports).
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
phentermine (Adipex-P) is a prescription Sympathomimetic Amine (Appetite Suppressant). Phentermine is used for a few weeks to help with weight loss.
Phentermine is a drug that can help you lose weight. It works by reducing your appetite.
Verify with FDA → · CMS NADAC pricing →
Drug Shortage Alert
phentermine is currently listed as to be discontinued by the FDA. Affected manufacturer: Teva Pharmaceuticals USA, Inc..
View all drug shortages →Drug Pricing (NADAC)
Generic Price
$2.48/unit
Generic Available
Yes (21 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Phentermine is used for a few weeks to help with weight loss.
Common side effects
Dry mouth, Difficulty sleeping, Constipation
Key warnings
Taking phentermine with other weight loss drugs is not recommended.
The sections below are summarized in plain English from phentermine's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Phentermine is a stimulant that affects your brain. It helps to decrease your appetite. This can help you eat less and lose weight.
Side Effects (from patient reports)
Based on 6,109 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for phentermine, by number of reports
- Nausea
Nausea
475 reports
- Pain
Pain
462 reports
- Fatigue
Fatigue
346 reports
- Headache
Headache
335 reports
- Anxiety
Anxiety
312 reports
- Vomiting
Vomiting
237 reports
- Dizziness
Dizziness
224 reports
- Chronic Kidney Disease
Chronic Kidney Disease
204 reports
- Diarrhoea
Diarrhoea
203 reports
- Weight Increased
Weight Increased
203 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for phentermine each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where phentermine sits
phentermine has more FDA adverse-event reports than 28% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is phentermine; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 6,109 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
6,109
Reports Mentioning Death
390
6.4% of reports — not proof of cause
Hospitalization Reports
1,481
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 2 | NAUSEA | 475 |
| 3 | PAIN | 462 |
| 4 | FATIGUE | 346 |
| 5 | HEADACHE | 335 |
| 6 | ANXIETY | 312 |
| 7 | VOMITING | 237 |
| 8 | DIZZINESS | 224 |
| 10 | CHRONIC KIDNEY DISEASE | 204 |
| 11 | DIARRHOEA | 203 |
| 12 | WEIGHT INCREASED | 203 |
| 13 | DYSPNOEA | 193 |
| 14 | DEPRESSION | 191 |
| 15 | ARTHRALGIA | 180 |
| 16 | ABDOMINAL PAIN | 165 |
| 17 | INSOMNIA | 162 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Taking phentermine with other weight loss drugs is not recommended. In rare cases, people have developed lung problems called pulmonary hypertension. Tell your doctor right away if you have shortness of breath, chest pain, fainting, or swelling in your legs. Phentermine can be habit-forming, so use it carefully.
Common Questions
Can I take phentermine with other weight loss medications?
What should I do if I experience shortness of breath while taking phentermine?
Can I drink alcohol while taking phentermine?
What if phentermine stops working for me?
Can I drive while taking phentermine?
What do I do if I take too much phentermine?
Can children take phentermine?
Does phentermine interact with any other medications?
What if I have kidney problems?
How long can I take phentermine?
What are the common side effects of phentermine?
What drug class is phentermine?
What pregnancy or breastfeeding source fields are listed for phentermine?
Is phentermine currently in shortage?
Related Medications in Sympathomimetic Amine (Appetite Suppressant)
Other drugs grouped near phentermine - same-class peers and common alternatives.
acarbose
Precose
Acarbose is a medicine that helps lower blood sugar levels in people with type 2 diabetes.
Compare with phentermine →
alogliptin
Nesina
Compare with phentermine →
bromocriptine
Cycloset
Bromocriptine (Cycloset) is a medicine that acts like dopamine in your body.
Compare with phentermine →
canagliflozin
Invokana
Invokana is a medicine used with diet and exercise to lower blood sugar in adults with type 2 diabetes.
Compare with phentermine →
colesevelam
Welchol
Colesevelam is a medicine that helps lower bad cholesterol (LDL-C) and control blood sugar in adults.
Compare with phentermine →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for phentermine: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 6,109.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 6.38%.
- budesonide Δ 0.00 pts · 55,389 reports · Corticosteroid 6.38%death share
- latanoprost Δ 0.00 pts · 48,513 reports · Prostaglandin Analog (Ophthalmic) 6.38%death share
- epinephrine Δ 0.00 pts · 61,536 reports · Adrenergic Agonist 6.39%death share
- icosapent ethyl Δ 0.01 pts · 7,801 reports · Omega-3 Fatty Acid (EPA) 6.37%death share
Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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What the FDA Data Shows for phentermine
The FDA label for phentermine (sold under brand names such as Adipex-P, Lomaira) classifies it as a prescription-only medication in the Sympathomimetic Amine (Appetite Suppressant) class. Phentermine is used for a few weeks to help with weight loss. Official labeling lists 3 commonly reported side effects, including Dry mouth, Difficulty sleeping, Constipation.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 6,109 voluntary reports. Interaction data is drawn directly from FDA-approved prescribing information. NADAC pricing from CMS shows a generic unit cost of $2.48.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC). Shortage status: FDA Drug Shortages Database.
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. This registry does not provide medication decisions.
Last updated: July 14, 2025
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages