Unifast

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Unifast

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Medically reviewed

Rosario Oropesa

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Unifast

What Type of Medicine is Unifast?

Unifast is a prescription-only medication that contains the active ingredient Phentermine, a synthetic compound classified as an anorectic agent (or anorexigenic agent). Medications in this category act to suppress appetite. The drug belongs to the sympathomimetic amine class, functioning as a central nervous system (CNS) stimulant. Unifast is typically a single-ingredient product, intended for use in adults with specific health criteria, such as a high Body Mass Index.

Unifast Composition and Available Form

The core composition of the medicine is Phentermine (often as the hydrochloride salt), delivered via the oral route in solid pharmaceutical preparations, specifically capsules or tablets. A key characteristic is the availability of both immediate-release and sustained-release formulations. Phentermine is a Schedule IV controlled substance. This regulatory status establishes its accepted medical use while requiring specialized monitoring.

What is the General Purpose of Unifast?

The general therapeutic purpose of Unifast is to provide targeted support for appetite suppression as an adjunct to a comprehensive lifestyle regimen. As a CNS stimulant, Phentermine works by influencing neurotransmitter release in the brain. This action results in increased satiety and reduced hunger, which assists the patient in adhering to necessary caloric restrictions to support overall weight management efforts.

Regulatory References

  1. MedlinePlus - NIH
  2. FDA
  3. FDA Drug Label
  4. [PubChem - NIH]

What side effects are possible with Unifast?

Possible side effects and safety information

The safety characteristics of this anorectic agent are officially classified across several System-Organ Classes, with specific safety notes related to duration of use and special populations. The most frequently documented adverse reactions, classified as common in official labeling, primarily affect the Central Nervous System and the Cardiovascular System. These include tachycardia (rapid heart rate), palpitations, elevated blood pressure, insomnia, tremor, dizziness, and restlessness.

Less common but officially listed effects involve the gastrointestinal system, such as dry mouth, constipation, and diarrhea. Psychotic episodes, dysphoria, and euphoria have also been documented, particularly at higher doses.

Serious Adverse Reactions and Safety Constraints

The regulatory profile highlights the potential for rare but serious adverse reactions, notably the risk of Primary Pulmonary Hypertension (PPH) and Valvular Heart Disease. These severe cardiovascular risks are primarily associated with prolonged use of anorectic agents. Due to its classification as a Schedule IV controlled substance, there is a recognized potential for dependence, and the label documents the risk of severe fatigue and depression following abrupt cessation after long-term use.

Population-Specific Safety Notes

The official labeling includes safety considerations for specific populations. Caution is advised for use in older adults (geriatric population), often recommending a lower starting dose due to potential decreases in hepatic, renal, or cardiac function. Safety notes also address patients with renal impairment due to the drug's excretion pathway. Furthermore, the label states that dosage requirements for antidiabetic medication may be altered in patients with Type 2 Diabetes Mellitus undergoing weight loss.

Overdose and Emergency Response

Unifast (Phentermine) overdose is officially documented as a severe medical event requiring immediate intervention. The clinical presentation is typically biphasic, starting with signs of extreme central nervous system (CNS) stimulation. These initial manifestations may include restlessness, tremor, hyperreflexia, confusion, panic states, and rapid respiration.

The overdose profile outlines significant cardiovascular risks, such as arrhythmia, tachycardia, and unstable blood pressure (hypertension followed by hypotension). The most serious and potentially fatal outcomes include circulatory collapse, convulsions, and coma. Immediate medical attention must be sought for any suspected overdosage. Emergency services should be contacted without delay if severe, life-threatening symptoms, such as seizures or collapse, are present.

Regulatory information confirms that no specific antidote is known for Phentermine intoxication. Consequently, the management of acute overdose is entirely symptomatic and supportive. Officially described procedures include the use of gastric lavage and the administration of sedation with a barbiturate to control acute stimulation. Patients with impaired renal function are noted to have a greater risk of toxic reactions due to the drug’s substantial renal excretion.

Therapeutic Uses of Unifast

What Unifast Treats: Main Uses and Benefits

Unifast is commonly used as a pharmacological aid in the overall management of Exogenous Obesity, a chronic condition characterized by excessive body fat accumulation. It is considered relevant for adults with an initial Body Mass Index (BMI) of 30 kg/m^2, or for those with a BMI of 27 kg/m^2 who are simultaneously managing weight-related complications such as high blood pressure or Type 2 Diabetes Mellitus. The therapeutic benefit plays a role in managing weight reduction efforts, which may contribute to easing the overall systemic burden related to these associated chronic conditions.

The primary symptomatic domain addressed is the patient's experience of frequent and intense excessive hunger or an inability to feel lasting satiety (fullness). This targeted support may help with adherence to the necessary reduced-calorie diet.

Quick Fact: Relief for Appetite Dysregulation
Assists with managing excessive hunger and supports the patient's experience of satiety during periods of required caloric restriction.

Regulatory References

  1. NIH DailyMed drug label

Eligibility and Restrictions for Use

Official Eligibility Criteria

Unifast (Phentermine) is a prescription medicine approved as a short-term adjunct to a weight reduction regimen. Eligibility is strictly defined by regulatory criteria regarding Body Mass Index (BMI) and the absence of specific pre-existing health conditions.

Eligibility scope Official Regulatory Statements
Populations Allowed Adults with Exogenous Obesity and an initial BMI 30 kg/m^2 or 27 kg/m^2 in the presence of risk factors (e.g., controlled Hypertension or Type 2 Diabetes Mellitus).
Populations Contraindicated Patients with a history of Cardiovascular Disease (e.g., coronary artery disease, stroke); Moderate-to-Severe Hypertension; Hyperthyroidism; Glaucoma; Agitated States; or a history of Drug Abuse.

Age and Condition Restrictions

Official labeling defines specific restrictions for certain populations:

  • Pediatric Use: Use is not recommended in patients leq 16 years of age; safety and effectiveness have not been established.
  • Pregnancy and Lactation: The medicine is contraindicated during Pregnancy (Pregnancy Category X) and is not recommended for Nursing Mothers due to the potential for serious adverse reactions in the infant.
  • Renal Function: Use requires caution in patients with renal impairment and is avoided in cases of End-Stage Renal Disease.
  • Drug History: The medicine is contraindicated within 14 days following the administration of a Monoamine Oxidase Inhibitor (MAOI).

What should I know about interactions with other medicines?

Interactions with other medicines and products — Official Regulatory Information for Unifast


Interaction Scope

Category Regulatory Status or Constraint
Medicinal product categories with documented interactions: Monoamine Oxidase Inhibitors (MAOIs), Adrenergic Neuron Blocking Drugs, Insulin and Oral Hypoglycemic Medications, and Other Drug Products for Weight Loss (including prescribed, over-the-counter, and herbal preparations).
Specific interacting medicines (if explicitly listed): Fenfluramine and Dexfenfluramine.
Mechanistic basis of interactions (only if stated in label): Primarily Pharmacodynamic interaction (additive sympathomimetic effects or opposing pharmacodynamic effects).
Timing-based interaction rules (if applicable): Must not be administered during or within 14 days following the administration of an MAOI.
Population-specific interaction notes (if applicable): Requirements for Insulin and Oral Hypoglycemic Medications in patients with diabetes may be altered.
Interaction-related restrictions: Coadministration is not recommended with other drug products intended for weight loss. Concomitant use with Alcohol may result in an adverse drug reaction.

Interaction Classifications (High-Level)

Category Classification Details based on Regulatory Documents
Interaction severity classification (as defined in official documents): Contraindicated Combination (with MAOIs); Warning/Precautionary Note (with Fenfluramine/Dexfenfluramine); Coadministration Not Recommended (with other weight-loss agents).
Interaction-context constraints (as defined in official documents): The 14-day separation rule for MAOIs and documented altered requirements for diabetes medications.

Resulting Interaction Structure

Official interaction statements:

  • Monoamine Oxidase Inhibitors (MAOIs) are officially contraindicated due to the potential risk of a Hypertensive Crisis, requiring a mandatory 14-day separation period.
  • Co-administration with Adrenergic Neuron Blocking Drugs may result in a decrease in their hypotensive effect.
  • The combination with Fenfluramine or Dexfenfluramine is associated with serious cardiac risks, including Primary Pulmonary Hypertension and Valvular Heart Disease.
  • Coadministration is not recommended with other drug products intended for weight loss, including certain herbal preparations.
  • Requirements for Insulin and Oral Hypoglycemic Medications may be altered, a documented systemic effect.

Connection to the overall interaction profile: The regulatory profile is dominated by serious pharmacodynamic interactions, particularly concerning sympathomimetic agents and cardiovascular safety, leading to restrictions and prohibitions. The structure defines a strict timing rule for MAOIs and notes a systemic adjustment interaction affecting diabetes management.

Mechanism of Action

The action of Unifast is strictly defined by its influence on the body's sympathomimetic pathways, primarily acting on the central nervous system to influence the hypothalamic signaling pathways and sympathetic outflow that govern appetite and metabolic rate. The mechanism involves a molecular cascade that increases synaptic neurotransmitter concentration, resulting in altered physiological signaling.

The active ingredient, Phentermine, initiates its effect by interacting with the Trace Amine-Associated Receptor 1 (TAAR1), a receptor on monoamine neurons. This interaction triggers the rapid reversal of the Norepinephrine (NET) and Dopamine (DAT) transporters. By operating in reverse, these transporters expel stored norepinephrine ( NE) and dopamine ( DA) directly into the synapse. This dramatically increases the local concentration of catecholamines available for postsynaptic binding.

The resulting high concentration of NE acts upon beta-adrenergic receptors located in the hypothalamus, the brain region controlling energy balance. This intense adrenergic receptor stimulation initiates a central feedback signal associated with satiety. This modification of central signaling alters the balance of neurobiological signaling that influences feeding impulses.

Beyond central effects, the increase in circulating NE leads to a generalized activation of the peripheral autonomic nervous system's sympathetic branch. This systemic action elevates the body’s sympathetic tone, which is directly correlated with an increase in the resting energy expenditure (metabolic rate).

Dosage and Administration Information

Unifast is an oral prescription medication intended for short-term use, typically limited to a few weeks, as an adjunct to a comprehensive weight reduction program. The method of administration and dosage must strictly follow the patterns established in clinical guidelines.

The dosage is individualized to find the lowest effective amount, with a common regimen being 37.5 mg taken once daily. This single dose is typically administered before breakfast or within one to two hours after the meal. For other formulations, such as the 8 mg tablet, the regimen requires administration three times a day, taken approximately 30 minutes before each meal. Regardless of the form, it is a key principle of use that the drug must be avoided in the late evening due to its central nervous system stimulating effects.

Correct use requires careful handling of the dosage form. Extended-release capsules must be swallowed whole and should not be crushed, broken, or chewed. Conversely, the 37.5 mg tablets are scored, allowing them to be divided for a prescribed twice-daily schedule.

Usage is subject to specific constraints. The medication should be discontinued if a loss of appetite-suppressant effect (tolerance) occurs. Furthermore, specific dose adjustments are required for certain populations. For adult patients with severe renal impairment, the maximum dose is reduced to 15 mg once daily, and the medication is not recommended for patients 16 years of age and younger.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Unifast

This section summarizes the official research evidence for Unifast (Phentermine), focusing on the types of studies conducted, the populations examined, and the outcomes measured, as reported by regulatory bodies and peer-reviewed scientific literature.


Research Evidence Investigating Exogenous Obesity Management

The research available for Unifast in conjunction with diet and lifestyle change primarily comes from short-term, placebo-controlled Randomized Controlled Trials (RCTs). These studies were designed to compare outcomes in groups receiving the medicine against groups receiving a placebo, both while following a reduced-calorie diet. Research was studied for outcomes related to physical discomfort stemming from appetite dysregulation and changes in key measurements.

Studies monitored several outcomes related to weight and body composition. Researchers primarily measured the change in total body weight during the study period. The studies reported measurements showing that a higher percentage of participants reached the threshold of 5% total body weight loss in the groups receiving the medicine compared to those receiving a placebo. Studies monitored reported changes during the study period concerning feelings of satiety (fullness) and patient-reported hunger intensity.


Duration of Research and Follow-up Data

Initial regulatory evaluation of Unifast included evidence from trials with limited follow-up durations, typically only assessing outcomes over mathbf12 weeks (a few weeks). The data are still emerging regarding the durability of weight change. Evidence often relies on longer-term observational cohort studies which track patient data over periods of up to two years. However, long-term effects are not fully established, and studies monitored and described patterns suggesting that weight regain often follows discontinuation of the treatment.


Unresolved Questions and Research Gaps

Despite the existing research, several areas remain insufficiently understood, and certainty remains low regarding certain aspects of treatment. The follow-up durations were limited in the most rigorous short-term RCTs, meaning there is limited information for long-term outcomes and maintenance. Data for groups like older adults are often limited and heterogeneous. Additionally, the data for certain high-risk subgroups remain insufficient, and subgroup findings are uncertain.

Key Studies & References

  1. Label: PHENTERMINE HCL capsule - DailyMed (Official US National Library of Medicine Drug Label)
  2. Safety and Effectiveness of Longer-Term Phentermine Use: Clinical Outcomes from an Electronic Health Record Cohort (Observational data on long-term outcomes and maintenance)

Frequently Asked Questions (FAQ)

Common questions about Unifast (FAQ)


Q: Is Unifast an antibiotic or a different type of medicine?

Unifast is officially classified as a sympathomimetic amine, which is a type of prescription medication that primarily acts on the central nervous system. This action is distinct from antibiotics. According to the regulatory mechanism of action, Unifast is intended to assist in reducing appetite.


Q: Are the side effects of Unifast known to be temporary or permanent?

Official safety information indicates that rare but serious side effects, such as Primary Pulmonary Hypertension, have been associated with prolonged use of this class of medication. Some common side effects listed in the product label are reported to appear early in the course of treatment, while others may require monitoring.


Q: What are the signs that a side effect is considered medically serious?

Official warnings describe several serious symptoms that warrant immediate attention. These include any signs of cardiac or respiratory distress, such as chest pain, unexplained shortness of breath, or feeling faint. Swelling of the lower legs or feet is also a symptom listed in the regulatory documents.


Q: Are there known interactions between Unifast and blood pressure or cholesterol medicines?

Regulatory documents confirm a potential interaction with certain blood pressure medications, specifically Adrenergic Neuron Blocking Drugs, which may reduce their blood-pressure-lowering effect. There are no major interaction categories that specifically list common cholesterol-lowering medicines. Professional review of all current medications is standard practice before starting treatment.


Q: Does Unifast interact with common vitamins or herbal supplements like St. John's Wort?

Official labeling advises caution when using Unifast with other products intended for weight loss, which includes certain herbal preparations. Since specific herbal supplements are not named individually in the regulatory document, the general caution for any product that affects the central nervous system applies.


Q: Is it necessary to avoid specific foods or beverages while taking Unifast?

According to the official product information, the concomitant use of alcohol may result in an adverse drug reaction. The regulatory label does not include restrictions on specific foods that need to be avoided while taking the medication.


Q: Are there any pre-existing medical conditions that are contraindications for Unifast use?

Yes, the official regulatory label lists several conditions that preclude the use of this medicine. These include pre-existing conditions such as advanced arteriosclerosis, severe uncontrolled high blood pressure, hyperthyroidism, and glaucoma. Unifast is contraindicated for individuals with a history of drug abuse.


Q: What are the non-drug-related substances that can interact with Unifast (e.g., caffeine)?

The most notable non-drug substance that may interact with Unifast is alcohol. The regulatory labeling explicitly warns that taking the medication with alcohol may result in an adverse drug reaction.


Q: What is the definition of a 'contraindication' related to Unifast use?

A contraindication is a medical term used to describe a condition or circumstance that makes the use of a particular medication potentially harmful or inappropriate. When a drug is officially contraindicated for a patient, it means the medicine is generally not administered.


Q: Why do some people on forums mention initial drowsiness when starting Unifast?

While the primary action of Unifast is stimulating and commonly leads to effects like restlessness or insomnia, the list of reported side effects does include general central nervous system effects such as dizziness and fatigue. This is factual information based on the official adverse reaction data.


Q: Can I safely take common over-the-counter pain relievers while using Unifast?

Official information indicates that caution is necessary with any drug that could increase blood pressure. Some common over-the-counter pain relievers can potentially increase the risk or severity of hypertension when combined with this type of medication.


Q: How long does it typically take to notice the full therapeutic effects of Unifast?

The regulatory label provides a guideline for checking effectiveness within the initial phase of treatment. The label suggests that effectiveness is generally assessed if a certain amount of weight is not lost within the initial four weeks of treatment.


Q: What are the general precautions about using Unifast during pregnancy or breastfeeding?

According to official regulatory documents, the use of Unifast is not recommended during pregnancy or while breastfeeding. Weight loss offers no known benefit to a pregnant woman and may cause fetal harm. The regulatory documents state that use is generally avoided or contraindicated during these periods due to the potential for serious adverse reactions in the infant.


Q: Does Unifast carry a specific FDA safety warning, such as a Boxed Warning?

The FDA label for Unifast monotherapy does not include a Boxed Warning, which is the specific regulatory term for the agency's strongest caution. However, the label does contain serious warnings, especially concerning the risks of Primary Pulmonary Hypertension and valvular heart disease.


Q: What does the patient information guide say about driving or operating machinery while on Unifast?

The official patient information indicates that the medication may impair a person's ability to engage in activities that require full attention. This includes potentially hazardous tasks such as driving a motor vehicle or operating heavy machinery. The patient information states that patients are cautioned about these potential effects.


Q: Is a generic version of Unifast widely available for purchase?

Yes, the active ingredient in Unifast, Phentermine, is widely available in generic form. This is confirmed by regulatory and official drug databases that track commercial availability.


Q: What is the recommended method for properly storing Unifast?

The official guidelines state that Unifast should be stored at room temperature and away from excessive moisture and heat. The regulatory information advises that the container should be kept tightly closed.


Q: Does Unifast have any known effects on fertility in men or women?

Regulatory studies have not been performed with the active ingredient to determine the potential for impairment of fertility in men or women.


Q: What is the process for safely disposing of unused or expired Unifast?

Unifast is classified as a Schedule IV controlled substance. The official guidance advises keeping the medicine in a secure location to prevent theft or misuse. For disposal, the guidance states that it is necessary to follow DEA and local guidelines, such as utilizing drug take-back programs.


Q: What are the factual signs of an overdose related to Unifast?

According to the official Overdosage section of the product information, symptoms of an acute overdose may include extreme restlessness, confusion, or hallucinations. Cardiovascular effects such as a rapid heart rate, high blood pressure, and in severe cases, circulatory collapse are also listed.

How should Unifast be stored and disposed of?

How to Store and Dispose of Unifast (Phentermine)

Official Storage Conditions

Unifast (Phentermine) must be stored at Controlled Room Temperature, defined by regulatory standards as 20 C to 25 C (68 F to 77 F), with permitted excursions up to 30 C. The product must be kept in a tightly closed container to ensure protection from moisture and to maintain stability until the expiration date. It is a mandatory requirement to keep this medicine out of the sight and reach of children due to its classification as a Schedule IV controlled substance.

Disposal Requirements

Unused or expired Unifast must be disposed of according to local regulations. If no official drug take-back program is available, the FDA recommends following the controlled substance protocol: mixing the medication with an unappealing substance, such as dirt or used coffee grounds, and placing the mixture in a sealed container before discarding in the household trash. All identifying information on the packaging must be removed or obscured prior to disposal.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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