Phentermine hydrochloride
Sympathomimetic amine anorectic. Sold as Phentermine hydrochloride, Lomaira.
Phentermine is the oldest weight loss medication still in common use in the United States, approved in 1959. Its label differs from the newer medications in one important way: it is approved for short-term use, described in the label as a few weeks, and not for long-term treatment.
Brands and what each one is approved for
One active ingredient can hold several separate FDA approvals. They are different documents with different approved uses, and mixing them up is the most common mistake made about these medications.
| Brand | Status for this use | Supply | Label version |
|---|---|---|---|
| Phentermine hydrochlorideSun Pharmaceutical Industries, Inc. | Approved for weight loss | Prescription | 14 July 2025 |
| LomairaCalvin Scott & Co., Inc. | Approved for weight loss | Prescription | 21 May 2026 |
How it works
Written by us
Phentermine is related to amphetamine and acts on the central nervous system. The label describes the effect as appetite suppression, and states that the exact mechanism by which it reduces weight is not fully established.
From the mechanism of action section of the Phentermine hydrochloride label
Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, amphetamine (d- and d / l-amphetamine). Drugs of this class used in obesity are commonly known as "anorectics" or "anorexigenics." It has not been established that the primary action of such drugs in treating obesity is one of...
What the FDA approved it for
The approved uses, as worded in the label.
From the FDA label
Phentermine hydrochloride
- Phentermine hydrochloride is indicated as a short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity for patients with an initial body mass index ≥ 30 kg/m 2, or ≥ 27 kg/m 2 in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia).
- Below is a chart of body mass index (BMI) based on various heights and weights.
- BMI is calculated by taking the patient's weight, in kilograms (kg), divided by the patient's height, in meters (m), squared.
- Metric conversions are as follows: pounds ÷ 2.2 = kg; inches × 0.0254 = meters.
Lomaira
- LOMAIRA™ tablets are indicated as a short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity in patients with an initial body mass index greater than or equal to 30 kg/m 2, or greater than or equal to 27 kg/m 2 in the presence of other risk factors (e.g., controlled hypertension,...
- Below is a chart of body mass index (BMI) based on various heights and weights.
- BMI is calculated by taking the patient's weight, in kilograms (kg), divided by the patient's height, in meters (m), squared.
- Metric conversions are as follows: pounds ÷ 2.2 = kg; inches x 0.0254 = meters.
Forms and strengths
The presentations and strengths listed in the label.
From the FDA label
Phentermine hydrochloride
- Tablets containing 37.5 mg phentermine hydrochloride (equivalent to 30 mg phentermine base).
- Tablets containing 37.5 mg phentermine hydrochloride.
Lomaira
LOMAIRA™ is available as follows: LOMAIRA™ 8 mg is supplied as white butterfly shaped tablets with blue speckles, debossed "K1" on one side and bisected on the other side.
How the label says it is taken
What the label states about administration. It is not a dosing instruction for any individual.
From the FDA label
Phentermine hydrochloride
- Dosage should be individualized to obtain an adequate response with the lowest effective dose.
- Late evening administration should be avoided (risk of insomnia).
- Phentermine hydrochloride tablets can be taken with or without food.
- Limit the dosage to 15 mg daily for patients with severe renal impairment (eGFR 15 to 29 mL/min/1.73 m 2)
Lomaira
- Dosage should be individualized to obtain an adequate response with the lowest effective dose.
- The usual adult dose is one tablet three times a day ½ hour before meals.
- This tablet is scored to facilitate administering one half of the usual dosage for patients not requiring the full dose.
- Phentermine hydrochloride is not recommended for use in pediatric patients less than or equal to 16 years of age.
Most common adverse reactions
The adverse reactions the label reports as most common.
From the FDA label
Phentermine hydrochloride
The following adverse reactions are described, or described in greater detail, in other sections: Primary pulmonary hypertension Valvular heart disease Effect on the ability to engage in potentially hazardous tasks Withdrawal effects following prolonged high dosage administration The following adverse reactions to phentermine have been identified: Cardiovascular Primary pulmonary hypertension...
Lomaira
The following adverse reactions are described, or described in greater detail, in other sections: - Primary pulmonary hypertension (see Warnings) - Valvular heart disease (see Warnings) - Effect on the ability to engage in potentially hazardous tasks (see Warnings) - Withdrawal effects following prolonged high dosage administration (see Drug Abuse and Dependence) The following adverse reactions...
Warnings and precautions
The warnings and precautions section of the label.
From the FDA label
Phentermine hydrochloride
- Coadministration with other drugs for weight loss is not recommended (safety and efficacy of combination not established).
- Rare cases of primary pulmonary hypertension have been reported. Phentermine should be discontinued in case of new, unexplained symptoms of dyspnea, angina pectoris, syncope or lower extremity edema.
- Rare cases of serious regurgitant cardiac valvular disease have been reported.
- Tolerance to the anorectic effect usually develops within a few weeks. If this occurs, phentermine should be discontinued. The recommended dose should not be exceeded.
- Phentermine may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle.
- Risk of abuse and dependence. The least amount feasible should be prescribed or dispensed at one time in order to minimize the possibility of overdosage.
- Concomitant alcohol use may result in an adverse drug reaction.
- Use caution in patients with even mild hypertension (risk of increase in blood pressure).
Lomaira
- Coadministration with Other Drug Products for Weight Loss LOMAIRA™ tablets are indicated only as short-term (a few weeks) monotherapy for the management of exogenous obesity.
- The safety and efficacy of combination therapy with phentermine and any other drug products for weight loss including prescribed drugs, over-the-counter preparations, and herbal products, or serotonergic agents such as selective serotonin reuptake inhibitors (e.g., fluoxetine, sertraline, fluvoxamine, paroxetine), have not been established.
- Therefore, coadministration of phentermine and these drug products is not recommended.
- Primary Pulmonary Hypertension Primary Pulmonary Hypertension (PPH) - a rare, frequently fatal disease of the lungs - has been reported to occur in patients receiving a combination of phentermine with fenfluramine or dexfenfluramine.
Contraindications
Situations in which the label states the medication must not be used.
From the FDA label
Phentermine hydrochloride
History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension) During or within 14 days following the administration of monoamine oxidase inhibitors Hyperthyroidism Glaucoma Agitated states History of drug abuse Pregnancy Nursing Known hypersensitivity, or idiosyncrasy to the sympathomimetic amines History of...
Lomaira
- History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension)
- During or within 14 days following the administration of monoamine oxidase inhibitors
- Hyperthyroidism
- Agitated states
- History of drug abuse
- Pregnancy (see Precautions)
- Nursing (see Precautions)
- Known hypersensitivity, or idiosyncrasy to the sympathomimetic amines
Drug interactions
Interactions the label singles out.
From the FDA label
Phentermine hydrochloride
- Monoamine oxidase inhibitors: Risk of hypertensive crisis.
- Alcohol: Consider potential interaction.
- Insulin and oral hypoglycemics: Requirements may be altered.
- Adrenergic neuron blocking drugs: Hypotensive effect may be decreased by phentermine.
Pregnancy and breastfeeding
The opening of the pregnancy section of the label. The full section is longer and is in the source document.
From the FDA label
Phentermine hydrochloride
Pregnancy Category X Phentermine is contraindicated during pregnancy because weight loss offers no potential benefit to a pregnant woman and may result in fetal harm. A minimum weight gain, and no weight loss, is currently recommended for all pregnant women, including those who are already overweight or obese, due to obligatory weight gain that occurs in maternal tissues during pregnancy.
Generic or brand
Written by us
Phentermine is available as a generic and has been for decades. It is also sold as Lomaira, an 8 mg tablet intended to be taken three times a day, and under other brand names at 37.5 mg.
The FDA label database lists 19 approved generic applications for this ingredient.
What affects the cost
Written by us
Phentermine is one of the least expensive medications in this category because generics have been available for many years. It is a controlled substance in the United States, which affects how it can be prescribed and dispensed.
Common questions
- Is phentermine approved for long-term weight loss?
- No. The label describes it as a short-term adjunct, a few weeks, in a weight reduction regimen based on exercise, behavioural modification and caloric restriction. The GLP-1 medications in this category are approved for long-term use, which is a substantive difference between them.
- Is phentermine a controlled substance?
- Yes, in the United States it is a Schedule IV controlled substance. The label includes a section on drug abuse and dependence.
Other medications under weight loss
Whether each one carries an FDA approval for this use is marked on its page and in this list.
Sources
Every fact above comes from one of these documents. The date is the effective date of the label version this page was built from.
FDA prescribing information for Phentermine hydrochloride
Sun Pharmaceutical Industries, Inc.. Label version 10, effective 14 July 2025.
FDA prescribing information for Lomaira
Calvin Scott & Co., Inc.. Label version 3, effective 21 May 2026.
Page last updated: 29 July 2026
Compiled by the HealthyStudy editorial team from FDA source documents. No medical reviewer is credited on this page, because none reviewed it.