phentermine
Brand names: Adipex-P, Lomaira
Phentermine is a drug that can help you lose weight. It works by reducing your appetite.
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.
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.
How to Take It
Take phentermine as your doctor tells you to. The usual dose is one 37.5 mg tablet daily. Take it before breakfast or 1 to 2 hours after breakfast. Some people may only need half a tablet (18.75 mg) daily, or half a tablet twice a day.
Pregnancy & Breastfeeding
Do not take phentermine if you are pregnant. Weight loss during pregnancy can harm the baby. Talk to your doctor about safe ways to manage your weight if you are pregnant or plan to become pregnant.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose.
Storage
Store phentermine at room temperature, away from light and moisture, and keep out of reach of children.
Side Effects (from patient reports)
Based on 3,337 FDA adverse event reports.
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
Death-Related Reports
390
Hospitalization Reports
1,481
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 537 |
| 2 | NAUSEA | 475 |
| 3 | PAIN | 462 |
| 4 | FATIGUE | 346 |
| 5 | HEADACHE | 335 |
| 6 | ANXIETY | 312 |
| 7 | VOMITING | 237 |
| 8 | DIZZINESS | 224 |
| 9 | OFF LABEL USE | 205 |
| 10 | CHRONIC KIDNEY DISEASE | 204 |
| 11 | DIARRHOEA | 203 |
| 12 | WEIGHT INCREASED | 203 |
| 13 | DYSPNOEA | 193 |
| 14 | DEPRESSION | 191 |
| 15 | ARTHRALGIA | 180 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) 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?
Is phentermine safe during pregnancy?
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.
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alogliptin
Nesina
Alogliptin and Metformin HCl is a drug that helps lower blood sugar in adults with type 2 diabetes.
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bromocriptine
Cycloset
Bromocriptine (Cycloset) is a medicine that acts like dopamine in your body.
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canagliflozin
Invokana
Invokana is a medicine used with diet and exercise to lower blood sugar in adults with type 2 diabetes.
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colesevelam
Welchol
Colesevelam is a medicine that helps lower bad cholesterol (LDL-C) and control blood sugar in adults.
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Related Health & Safety Data
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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 3,337 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 further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
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. Always consult a healthcare professional before making medication decisions.
Last updated: July 14, 2025
Read our methodology — how this data is sourced, computed, and verified.
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