Phentermine Hcl 15mg Capsules
It is used for weight loss.
Drug Class
Anorexiant
Pharmacologic Class
Sympathomimetic amine
Pregnancy Category
Not available
FDA Approved
May 1959
DEA Schedule
Schedule IV
Overview
What is this medicine?
Phentermine is a prescription medication used for a short period of time to help people lose weight. It works by decreasing your appetite. It should be used along with a doctor-approved diet, exercise, and behavior change program.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, it's essential to take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. The dosage schedule may vary depending on the specific product you're taking. Some products are designed to be taken once a day, either before breakfast or 1 to 2 hours after breakfast. Others may need to be taken multiple times a day, approximately 30 minutes before meals. Make sure you understand the correct dosage schedule for your medication.
To minimize potential sleep disturbances, avoid taking your medication late in the evening. If you have any questions or concerns about taking your medication, be sure to discuss them with your doctor or pharmacist.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry place, away from the bathroom. Keep your medication in a secure location where children cannot see or reach it, and where others cannot access it. Consider using a locked box or area to store your medication. It's also important to keep all medications out of reach of pets.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless specifically instructed to do so. Instead, consult with your pharmacist to determine the best disposal method. You may also want to explore local drug take-back programs in your area.
What to Do If You Miss a Dose
If you miss a dose of your medication, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosage schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To get the most benefit from your medication, it's essential to take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. The dosage schedule may vary depending on the specific product you're taking. Some products are designed to be taken once a day, either before breakfast or 1 to 2 hours after breakfast. Others may need to be taken multiple times a day, approximately 30 minutes before meals. Make sure you understand the correct dosage schedule for your medication.
To minimize potential sleep disturbances, avoid taking your medication late in the evening. If you have any questions or concerns about taking your medication, be sure to discuss them with your doctor or pharmacist.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry place, away from the bathroom. Keep your medication in a secure location where children cannot see or reach it, and where others cannot access it. Consider using a locked box or area to store your medication. It's also important to keep all medications out of reach of pets.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless specifically instructed to do so. Instead, consult with your pharmacist to determine the best disposal method. You may also want to explore local drug take-back programs in your area.
What to Do If You Miss a Dose
If you miss a dose of your medication, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosage schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Follow a reduced-calorie diet as prescribed by your doctor or dietitian.
- Engage in regular physical activity.
- Adopt healthy eating habits and portion control.
- Avoid taking phentermine late in the day to prevent insomnia.
- Do not stop taking phentermine suddenly after prolonged use, as withdrawal symptoms may occur.
Available Forms & Alternatives
Dosing & Administration
Adult Dosing
Standard Dose:
15 mg once daily in the morning, before breakfast or 1-2 hours after breakfast.
Dose Range:
15 - 37.5 mg
Condition-Specific Dosing:
obesity:
Initial dose of 15 mg or 30 mg once daily, adjusted based on response and tolerability. Maximum 37.5 mg daily.
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Not established (Safety and efficacy not established in patients under 16 years of age).
Adolescent:
Not established (Safety and efficacy not established in patients under 16 years of age).
Dose Adjustments
Renal Impairment:
Mild:
No specific dose adjustment recommended, but use with caution.
Moderate:
Use with caution; consider lower doses or extended intervals. Contraindicated in severe renal impairment.
Severe:
Contraindicated
Dialysis:
Contraindicated
Hepatic Impairment:
Mild:
Use with caution.
Moderate:
Use with caution; consider lower doses. Contraindicated in severe hepatic impairment.
Severe:
Contraindicated
Pharmacology
Mechanism of Action
Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, the amphetamines. Actions include central nervous system stimulation and elevation of blood pressure. It is believed to exert its anorexigenic effect primarily through the release of norepinephrine from nerve terminals in the hypothalamus, which stimulates the satiety center, leading to appetite suppression. It may also have some effect on dopamine and serotonin.
Pharmacokinetics
Absorption:
Bioavailability:
Not precisely quantified, but well absorbed from the GI tract.
Tmax:
3-4.4 hours
FoodEffect:
Food may slightly delay absorption but does not significantly affect overall bioavailability.
Distribution:
Vd:
Not precisely quantified, but widely distributed.
ProteinBinding:
Approximately 17%
CnssPenetration:
Yes
Elimination:
HalfLife:
19-24 hours (highly variable, pH-dependent)
Clearance:
Primarily renal clearance, pH-dependent.
ExcretionRoute:
Renal (urine)
Unchanged:
70-80% (at acidic urine pH)
Pharmacodynamics
OnsetOfAction:
Within 1-2 hours
PeakEffect:
3-4.4 hours (corresponds to Tmax)
DurationOfAction:
Approximately 12-14 hours (due to long half-life, effects can last throughout the day)
Confidence:
Medium
Safety & Warnings
Side Effects
Serious Side Effects: Seek Medical Help Immediately
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of high blood pressure, including:
+ Severe headache or dizziness
+ Passing out
+ Changes in eyesight
Changes in behavior or mood
Shakiness
Rare but serious side effects, such as heart valve problems or increased pressure in the lungs, which can be fatal. If you experience any of the following, seek medical help immediately:
+ Dizziness or passing out
+ Persistent tiredness or weakness
+ Fast or abnormal heartbeat
+ Chest pain
+ Shortness of breath
+ Swelling in your arms or legs
+ Decreased ability to exercise
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects, contact your doctor or seek medical help if they bother you or persist:
Dizziness or headache
Feeling nervous or excitable
Diarrhea or constipation
Dry mouth
Trouble sleeping
Bad taste in your mouth
Decreased interest in sex
Difficulty getting or maintaining an erection
Restlessness
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of high blood pressure, including:
+ Severe headache or dizziness
+ Passing out
+ Changes in eyesight
Changes in behavior or mood
Shakiness
Rare but serious side effects, such as heart valve problems or increased pressure in the lungs, which can be fatal. If you experience any of the following, seek medical help immediately:
+ Dizziness or passing out
+ Persistent tiredness or weakness
+ Fast or abnormal heartbeat
+ Chest pain
+ Shortness of breath
+ Swelling in your arms or legs
+ Decreased ability to exercise
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects, contact your doctor or seek medical help if they bother you or persist:
Dizziness or headache
Feeling nervous or excitable
Diarrhea or constipation
Dry mouth
Trouble sleeping
Bad taste in your mouth
Decreased interest in sex
Difficulty getting or maintaining an erection
Restlessness
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe headache
- Blurred vision
- Chest pain
- Shortness of breath
- Swelling in your ankles or feet
- Fainting
- Unusual changes in mood or behavior (e.g., severe anxiety, agitation, hallucinations)
- Palpitations or very fast heartbeat
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following conditions and situations to ensure safe treatment:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Describe the allergic reaction and its symptoms.
A history of heart disease, including heart failure or abnormal heart rhythms, as well as high blood pressure or stroke.
Presence of glaucoma, agitation, anxiety, or an overactive thyroid gland.
Kidney disease or being on dialysis.
Recent use (within the last 14 days) of certain medications for depression or Parkinson's disease, such as isocarboxazid, phenelzine, tranylcypromine, selegiline, or rasagiline, as this can lead to severely high blood pressure.
Current use of fluoxetine, fluvoxamine, linezolid, methylene blue, paroxetine, or sertraline.
Use of any other weight loss medications, whether prescription, over-the-counter, or natural products.
Pregnancy or the possibility of being pregnant. This medication should not be taken during pregnancy.
* Breast-feeding. You should not breast-feed while taking this medication.
This list is not exhaustive, and it is crucial to discuss all your health conditions and medications with your doctor and pharmacist. This includes prescription and over-the-counter drugs, natural products, and vitamins. Your healthcare provider needs this information to assess the safety of taking this medication with your other treatments and health conditions. Never start, stop, or adjust the dose of any medication without first consulting your doctor.
It is essential to inform your doctor about the following conditions and situations to ensure safe treatment:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Describe the allergic reaction and its symptoms.
A history of heart disease, including heart failure or abnormal heart rhythms, as well as high blood pressure or stroke.
Presence of glaucoma, agitation, anxiety, or an overactive thyroid gland.
Kidney disease or being on dialysis.
Recent use (within the last 14 days) of certain medications for depression or Parkinson's disease, such as isocarboxazid, phenelzine, tranylcypromine, selegiline, or rasagiline, as this can lead to severely high blood pressure.
Current use of fluoxetine, fluvoxamine, linezolid, methylene blue, paroxetine, or sertraline.
Use of any other weight loss medications, whether prescription, over-the-counter, or natural products.
Pregnancy or the possibility of being pregnant. This medication should not be taken during pregnancy.
* Breast-feeding. You should not breast-feed while taking this medication.
This list is not exhaustive, and it is crucial to discuss all your health conditions and medications with your doctor and pharmacist. This includes prescription and over-the-counter drugs, natural products, and vitamins. Your healthcare provider needs this information to assess the safety of taking this medication with your other treatments and health conditions. Never start, stop, or adjust the dose of any medication without first consulting your doctor.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
When starting this medication, be cautious and avoid driving or engaging in activities that require your full attention until you understand how it affects you.
Adhere to your doctor's instructions regarding the duration of treatment. Do not take this medication for longer than prescribed. Prolonged use or high doses may lead to tolerance, where the medication becomes less effective, and higher doses may be required to achieve the same effect. If you notice the medication is not working as well as it previously did, contact your doctor. Do not exceed the recommended dose.
If you have been taking this medication for an extended period, consult your doctor before stopping treatment. You may need to gradually taper off the medication to avoid potential withdrawal effects. Be aware that this medication can be habit-forming, and long-term use should be avoided. If you have a history of substance or alcohol abuse, inform your doctor.
Before initiating treatment, your doctor may recommend heart tests to ensure your safety while taking this medication. If you have any questions or concerns, discuss them with your doctor.
Regularly monitor your blood pressure and heart rate as directed by your doctor.
If you have diabetes and are taking medications to manage your blood sugar levels, consult your doctor. Weight loss associated with this medication may increase the risk of hypoglycemia (low blood sugar) if you are taking diabetes medications. Be aware of the signs of hypoglycemia, which include dizziness, headache, drowsiness, weakness, shaking, rapid heartbeat, confusion, hunger, and sweating. If you experience any of these symptoms, contact your doctor immediately.
Follow the diet and exercise plan recommended by your doctor to ensure safe and effective treatment.
Before consuming alcohol, discuss the potential risks and benefits with your doctor.
This medication is not approved for use in children under 17 years of age.
When starting this medication, be cautious and avoid driving or engaging in activities that require your full attention until you understand how it affects you.
Adhere to your doctor's instructions regarding the duration of treatment. Do not take this medication for longer than prescribed. Prolonged use or high doses may lead to tolerance, where the medication becomes less effective, and higher doses may be required to achieve the same effect. If you notice the medication is not working as well as it previously did, contact your doctor. Do not exceed the recommended dose.
If you have been taking this medication for an extended period, consult your doctor before stopping treatment. You may need to gradually taper off the medication to avoid potential withdrawal effects. Be aware that this medication can be habit-forming, and long-term use should be avoided. If you have a history of substance or alcohol abuse, inform your doctor.
Before initiating treatment, your doctor may recommend heart tests to ensure your safety while taking this medication. If you have any questions or concerns, discuss them with your doctor.
Regularly monitor your blood pressure and heart rate as directed by your doctor.
If you have diabetes and are taking medications to manage your blood sugar levels, consult your doctor. Weight loss associated with this medication may increase the risk of hypoglycemia (low blood sugar) if you are taking diabetes medications. Be aware of the signs of hypoglycemia, which include dizziness, headache, drowsiness, weakness, shaking, rapid heartbeat, confusion, hunger, and sweating. If you experience any of these symptoms, contact your doctor immediately.
Follow the diet and exercise plan recommended by your doctor to ensure safe and effective treatment.
Before consuming alcohol, discuss the potential risks and benefits with your doctor.
This medication is not approved for use in children under 17 years of age.
Overdose Information
Overdose Symptoms:
- Restlessness
- Tremor
- Hyperreflexia
- Rapid breathing
- Confusion
- Assaultiveness
- Hallucinations
- Panic states
- High fever
- Rhabdomyolysis
- Arrhythmias
- Hypertension or hypotension
- Circulatory collapse
- Nausea
- Vomiting
- Diarrhea
- Abdominal cramps
- Convulsions
- Coma
What to Do:
Seek immediate medical attention. Call 911 or Poison Control at 1-800-222-1222. Management is largely supportive, including gastric lavage, activated charcoal, and sedation for CNS overstimulation.
Drug Interactions
Contraindicated Interactions
- Monoamine Oxidase Inhibitors (MAOIs) - risk of hypertensive crisis
- Other sympathomimetic amines (e.g., other anorectic agents, decongestants) - risk of additive effects and severe hypertension
- Fenfluramine, Dexfenfluramine (historical, due to primary pulmonary hypertension and valvular heart disease)
Major Interactions
- Alcohol - increased CNS effects
- Antihypertensive agents (e.g., guanethidine, clonidine, methyldopa) - phentermine may antagonize their hypotensive effects
- Serotonergic drugs (e.g., SSRIs, SNRIs, triptans, tricyclic antidepressants) - theoretical risk of serotonin syndrome
- Insulin and oral hypoglycemic agents - may alter blood glucose levels, requiring dose adjustment
Moderate Interactions
- Caffeine and other CNS stimulants - additive stimulant effects
- Urinary alkalinizers (e.g., sodium bicarbonate, acetazolamide) - decrease phentermine excretion, increasing levels and duration of action
- Urinary acidifiers (e.g., ammonium chloride, ascorbic acid) - increase phentermine excretion, decreasing levels and duration of action
Minor Interactions
- Not available
Monitoring
Baseline Monitoring
Blood Pressure (BP)
Rationale: Phentermine can cause significant increases in BP.
Timing: Prior to initiation
Heart Rate (HR)
Rationale: Phentermine can cause tachycardia.
Timing: Prior to initiation
Weight and BMI
Rationale: To establish baseline and track efficacy.
Timing: Prior to initiation
Medical history (especially cardiovascular, psychiatric, thyroid)
Rationale: To identify contraindications or risk factors.
Timing: Prior to initiation
Routine Monitoring
Blood Pressure (BP)
Frequency: Regularly (e.g., weekly for first few weeks, then monthly)
Target: Within patient's normal range or target for hypertension management
Action Threshold: Significant or sustained elevation requiring dose adjustment or discontinuation
Heart Rate (HR)
Frequency: Regularly (e.g., weekly for first few weeks, then monthly)
Target: Within patient's normal range
Action Threshold: Persistent tachycardia or palpitations
Weight and BMI
Frequency: Monthly
Target: Progressive weight loss (e.g., 5% in 12 weeks)
Action Threshold: Lack of adequate weight loss after 12 weeks (e.g., <3% to 5%) may warrant discontinuation
Symptoms of primary pulmonary hypertension (PPH) or valvular heart disease
Frequency: Periodically
Target: Absence of symptoms
Action Threshold: Dyspnea, angina pectoris, syncope, or lower extremity edema
Mental status/mood
Frequency: Periodically
Target: Stable mood, absence of agitation or psychosis
Action Threshold: New or worsening anxiety, insomnia, agitation, or psychotic symptoms
Symptom Monitoring
- Chest pain
- Shortness of breath (dyspnea)
- Fainting (syncope)
- Swelling in legs/ankles (edema)
- Palpitations
- Dizziness
- Insomnia
- Nervousness
- Dry mouth
- Constipation
- Headache
Special Patient Groups
Pregnancy
Contraindicated in pregnancy due to potential for fetal harm (e.g., increased risk of congenital anomalies, withdrawal symptoms in neonates). Weight loss during pregnancy offers no benefit and may cause fetal harm.
Trimester-Specific Risks:
First Trimester:
Potential for increased risk of congenital anomalies.
Second Trimester:
Not recommended; weight loss is not advised.
Third Trimester:
Not recommended; weight loss is not advised; potential for neonatal withdrawal.
Lactation
Contraindicated during breastfeeding. Phentermine is excreted into breast milk and could cause serious adverse reactions in a breastfed infant (e.g., irritability, sleep disturbances, cardiovascular effects).
Infant Risk:
High (L5)
Pediatric Use
Safety and effectiveness have not been established in pediatric patients under 16 years of age. Use is generally not recommended.
Geriatric Use
Use with caution in elderly patients (65 years and older) due to a greater likelihood of decreased renal function and increased sensitivity to sympathomimetic effects (e.g., cardiovascular effects, CNS stimulation). Start with lower doses and monitor closely.
Clinical Information
Clinical Pearls
- Phentermine is intended for short-term use (a few weeks) as part of a comprehensive weight management program.
- Tolerance to the anorectic effect may develop within a few weeks; increasing the dose is not recommended.
- Patients should be advised to take the dose early in the morning to avoid insomnia.
- Monitor for signs of primary pulmonary hypertension (PPH) and valvular heart disease, although these are rare with phentermine monotherapy, they were associated with combination use (e.g., 'fen-phen').
- Abrupt discontinuation after prolonged high-dose therapy may result in extreme fatigue and mental depression.
Alternative Therapies
- Liraglutide (Saxenda)
- Semaglutide (Wegovy)
- Naltrexone/Bupropion (Contrave)
- Orlistat (Xenical, Alli)
- Bariatric surgery (for severe obesity)
- Lifestyle modifications (diet, exercise, behavioral therapy)
Cost & Coverage
Average Cost:
$15 - $50 per 30 capsules (15mg)
Generic Available:
Yes
Insurance Coverage:
Tier 2 or Tier 3 (often requires prior authorization for weight loss medications)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about your medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek medical attention. When seeking help, be prepared to provide details about the medication taken, the amount, and the time it happened.