PlainMeds provides educational information only. This is not medical advice. Always consult your doctor or pharmacist.

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 →

View Alternatives → Compare with Another Drug → Full Side Effects Report →

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.

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.

This is a plain-language summary of phentermine's FDA labeling, not individualized dosing advice. Ask a pharmacist or prescriber before changing how you take this medication.

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.

This is a plain-language summary of phentermine's FDA labeling, not individualized advice. Ask a pharmacist or prescriber about pregnancy or breastfeeding on this medication.

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.

This is a plain-language summary of phentermine's FDA labeling, not individualized advice. Ask a pharmacist or prescriber what to do about your specific 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 6,109 FDA adverse event reports.

Most-reported reactions

Adverse reactions in FAERS for phentermine, by number of reports

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.

Source FDA Adverse Event Reporting System (FAERS) As of 2025

Reports over time

Adverse-event reports filed for phentermine each year to the FDA Adverse Event Reporting System (FAERS).

0200400600 20042007201020132016201920222025 544

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.

fewest reports most reports

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

Female 4,729 (85%)
Male 772 (14%)

Age Distribution

0–17 51
18–44 1,819
45–64 1,667
65–74 251
75+ 54

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

COMPLETED SUICIDE 95
DRUG ABUSE 91
TOXICITY TO VARIOUS AGENTS 77
DEATH 60
CARDIO-RESPIRATORY ARREST 43
CARDIAC ARREST 42
RESPIRATORY ARREST 33
OVERDOSE 17
POISONING 15
ACUTE KIDNEY INJURY 12

Reactions in Hospitalization Reports

PAIN 186
NAUSEA 154
ANXIETY 134
PULMONARY EMBOLISM 127
INJURY 110
VOMITING 100
DEEP VEIN THROMBOSIS 98
ABDOMINAL PAIN 90
DYSPNOEA 86
CHOLECYSTITIS CHRONIC 83

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?
No, it is not recommended to take phentermine with other weight loss medications.
What should I do if I experience shortness of breath while taking phentermine?
Stop taking phentermine and contact your doctor immediately.
Can I drink alcohol while taking phentermine?
Drinking alcohol with phentermine may cause unwanted side effects.
What if phentermine stops working for me?
If phentermine stops working, stop taking it and talk to your doctor.
Can I drive while taking phentermine?
Phentermine may affect your ability to drive or operate machinery. Be careful until you know how it affects you.
What do I do if I take too much phentermine?
Call your doctor or go to the emergency room right away.
Can children take phentermine?
No, phentermine is not recommended for children under 16 years old.
Does phentermine interact with any other medications?
Yes, phentermine can interact with other medications, especially MAO inhibitors, alcohol, insulin and oral hypoglycemics, and adrenergic neuron blocking drugs. Tell your doctor about all the medications you take.
What if I have kidney problems?
If you have kidney problems, talk to your doctor before taking phentermine. The dose may need to be adjusted.
How long can I take phentermine?
Phentermine is meant for short-term use, usually a few weeks.
What are the common side effects of phentermine?
The most commonly reported side effects of phentermine include Dry mouth, Difficulty sleeping, Constipation. Based on 6,109 FDA adverse event reports. Always consult your healthcare provider about potential side effects.
What drug class is phentermine?
phentermine belongs to the Sympathomimetic Amine (Appetite Suppressant) drug class. It requires a prescription (Rx). Phentermine is used for a few weeks to help with weight loss.
Is phentermine safe during pregnancy?
Do not take phentermine if you are pregnant. Weight loss during pregnancy can harm the baby. Always consult your healthcare provider before using any medication during pregnancy or breastfeeding.
Is phentermine currently in shortage?
Yes, phentermine is currently listed as to be discontinued by the FDA. Affected manufacturer: Teva Pharmaceuticals USA, Inc.. Visit the FDA Drug Shortages database for the latest updates.

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 phentermine vs acarbose side-by-side →

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

Why some drugs demand precise dosing and monitoring

Common Drug Interactions

Dangerous medication combinations and how to protect yourself

Save on phentermine

Compare prices and find discounts at pharmacies near you. Free coupons can save up to 80% on prescriptions.

Check Prices on GoodRx →

Disclosure: This link may earn us a commission at no extra cost to you. See our terms.

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 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.

Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled and last refreshed May 2026. See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a correction.

All federal data sources used on this page