Adipex-P 37.5mg Tablets
It is used for weight loss.
Drug Class
Anorexiant
Pharmacologic Class
Centrally acting sympathomimetic amine
Pregnancy Category
Category X
FDA Approved
May 1959
DEA Schedule
Schedule IV
Overview
What is this medicine?
Phentermine is a prescription medication used for short-term weight loss. It works by affecting certain chemicals in your brain to help reduce your appetite, making you feel less hungry and more full. 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 quality 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, check with your pharmacist for guidance on 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 quality 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, check with your pharmacist for guidance on 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 as recommended by your healthcare provider.
- Implement behavioral changes to support weight loss (e.g., portion control, mindful eating, stress management).
- Avoid alcohol while taking phentermine, as it can increase side effects.
- Do not take phentermine in the evening, as it can cause insomnia.
Available Forms & Alternatives
Available Strengths:
Generic Alternatives:
Dosing & Administration
Adult Dosing
Standard Dose:
37.5 mg orally once daily in the morning, or 18.75 mg orally twice daily (before breakfast and before lunch)
Dose Range:
15 - 37.5 mg
Condition-Specific Dosing:
obesity:
Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification, and caloric restriction in patients with an initial BMI of 30 kg/m² or greater, or 27 kg/m² or greater in the presence of other risk factors (e.g., hypertension, diabetes, hyperlipidemia).
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Not established (contraindicated in children under 16 years of age)
Adolescent:
Not established (contraindicated in children under 16 years of age)
Dose Adjustments
Renal Impairment:
Mild:
Use with caution; consider lower dose (e.g., 15 mg daily)
Moderate:
Use with caution; consider lower dose (e.g., 15 mg daily)
Severe:
Contraindicated (due to significant renal excretion)
Dialysis:
Not recommended; contraindicated
Hepatic Impairment:
Mild:
Use with caution; no specific dose adjustment guidelines
Moderate:
Use with caution; no specific dose adjustment guidelines
Severe:
Use with caution; no specific dose adjustment guidelines
Pharmacology
Mechanism of Action
Phentermine is a sympathomimetic amine with pharmacologic activity similar to the amphetamines. It stimulates the release of norepinephrine from nerve terminals in the hypothalamus, leading to appetite suppression. It also causes the release of dopamine and, to a lesser extent, serotonin. The primary effect is thought to be mediated through the central nervous system, specifically the satiety center in the lateral hypothalamic area.
Pharmacokinetics
Absorption:
Bioavailability:
Not precisely quantified, but well absorbed
Tmax:
3-4.4 hours
FoodEffect:
Can be taken with or without food; food may slightly delay absorption but does not significantly affect overall bioavailability.
Distribution:
Vd:
Not precisely quantified, but widely distributed
ProteinBinding:
Approximately 17.5%
CnssPenetration:
Yes
Elimination:
HalfLife:
19-24 hours (range 16-31 hours)
Clearance:
Primarily renal
ExcretionRoute:
Renal (urine)
Unchanged:
60-80% (highly dependent on urinary pH; increased excretion with acidic urine)
Pharmacodynamics
OnsetOfAction:
Within 1-2 hours
PeakEffect:
3-4.4 hours
DurationOfAction:
Approximately 12-14 hours (for 37.5 mg dose)
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
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 immediately:
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
+ Dizziness
+ Passing out
+ Changes in eyesight
Changes in behavior or mood
Shakiness
Rare but serious heart valve problems or increased pressure in the lungs, which can be life-threatening. If you experience any of the following, call your doctor right away:
+ 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, or if they bother you or persist, contact your doctor or seek medical help:
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
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns, contact 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 immediately:
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
+ Dizziness
+ Passing out
+ Changes in eyesight
Changes in behavior or mood
Shakiness
Rare but serious heart valve problems or increased pressure in the lungs, which can be life-threatening. If you experience any of the following, call your doctor right away:
+ 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, or if they bother you or persist, contact your doctor or seek medical help:
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
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns, contact 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 chest pain, shortness of breath, or fainting (signs of pulmonary hypertension or heart problems)
- Swelling in your ankles or feet
- Severe headache, blurred vision, or pounding in your neck or ears (signs of high blood pressure)
- Unusual changes in mood or behavior, severe nervousness, or agitation
- Signs of an allergic reaction (e.g., rash, hives, swelling of face/lips/tongue/throat, difficulty breathing)
- Signs of drug dependence or withdrawal if stopped suddenly (e.g., extreme fatigue, depression)
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:
Any allergies you have, including allergies to this medication, its components, or other substances. Describe the allergic reaction and its symptoms.
A history of certain health conditions, such as:
+ Heart disease, including heart failure or abnormal heart rhythms
+ Drug abuse
+ High blood pressure
+ Stroke
The presence of other health conditions, including:
+ Glaucoma
+ Agitation
+ Anxiety
+ Overactive thyroid (hyperthyroidism)
Kidney disease or dialysis treatment
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 may increase the risk of very high blood pressure
Current use of any of the following medications:
+ Fluoxetine
+ Fluvoxamine
+ Linezolid
+ Methylene blue
+ Paroxetine
+ Sertraline
Use of any other weight loss medications (prescription or over-the-counter)
Pregnancy or potential pregnancy, as this medication should not be taken during pregnancy
* Breast-feeding, as this medication is not recommended for nursing mothers
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions with your doctor and pharmacist to ensure safe use. Do not initiate, stop, or modify any medication without consulting your doctor.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances. Describe the allergic reaction and its symptoms.
A history of certain health conditions, such as:
+ Heart disease, including heart failure or abnormal heart rhythms
+ Drug abuse
+ High blood pressure
+ Stroke
The presence of other health conditions, including:
+ Glaucoma
+ Agitation
+ Anxiety
+ Overactive thyroid (hyperthyroidism)
Kidney disease or dialysis treatment
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 may increase the risk of very high blood pressure
Current use of any of the following medications:
+ Fluoxetine
+ Fluvoxamine
+ Linezolid
+ Methylene blue
+ Paroxetine
+ Sertraline
Use of any other weight loss medications (prescription or over-the-counter)
Pregnancy or potential pregnancy, as this medication should not be taken during pregnancy
* Breast-feeding, as this medication is not recommended for nursing mothers
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions with your doctor and pharmacist to ensure safe use. Do not initiate, stop, or modify any medication without 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 prescribed treatment duration and dosage instructions. Do not take this medication for an extended period beyond what your doctor recommends. Long-term use or high doses can lead to tolerance, where the medication may not be as effective, and you may require higher doses 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 prescribed dosage.
If you have been taking this medication for an extended period, consult your doctor before stopping its use. Your doctor may recommend gradually tapering off the medication to minimize 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 with this medication, your doctor may require you to undergo certain heart tests. If you have any questions or concerns, discuss them with your doctor.
Monitor your blood pressure and heart rate as instructed 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 your 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.
Before consuming alcohol, discuss its potential effects with your doctor.
This medication is not intended for children under the age of 17.
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 prescribed treatment duration and dosage instructions. Do not take this medication for an extended period beyond what your doctor recommends. Long-term use or high doses can lead to tolerance, where the medication may not be as effective, and you may require higher doses 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 prescribed dosage.
If you have been taking this medication for an extended period, consult your doctor before stopping its use. Your doctor may recommend gradually tapering off the medication to minimize 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 with this medication, your doctor may require you to undergo certain heart tests. If you have any questions or concerns, discuss them with your doctor.
Monitor your blood pressure and heart rate as instructed 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 your 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.
Before consuming alcohol, discuss its potential effects with your doctor.
This medication is not intended for children under the age of 17.
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 or call Poison Control at 1-800-222-1222. Treatment is largely supportive and symptomatic, including gastric lavage, activated charcoal, and sedation for severe CNS overstimulation. Intravenous phentolamine may be used for severe hypertension.
Drug Interactions
Contraindicated Interactions
- Monoamine Oxidase Inhibitors (MAOIs) - concurrent use or within 14 days of MAOI discontinuation (risk of hypertensive crisis)
- Other centrally acting appetite suppressants (e.g., fenfluramine, dexfenfluramine, sibutramine) - risk of pulmonary hypertension and valvular heart disease
- Other stimulants (e.g., amphetamines, methylphenidate) - increased risk of cardiovascular and CNS adverse effects
Major Interactions
- Alcohol - increased risk of CNS adverse effects (dizziness, confusion)
- Antihypertensive agents (e.g., beta-blockers, ACE inhibitors) - phentermine may antagonize the hypotensive effects
- Serotonergic drugs (e.g., SSRIs, SNRIs, TCAs, triptans, St. John's Wort) - theoretical risk of serotonin syndrome
- Insulin and oral hypoglycemic agents - may alter blood glucose levels, requiring dose adjustment of antidiabetic medications
Moderate Interactions
- Adrenergic neuron blocking drugs (e.g., guanethidine) - phentermine may decrease their hypotensive effect
- Thyroid hormones - may increase stimulant effects
Minor Interactions
- Caffeine - additive stimulant effects
Monitoring
Baseline Monitoring
Blood Pressure (BP)
Rationale: Phentermine can cause significant increases in BP, especially in patients with pre-existing hypertension.
Timing: Prior to initiation of therapy
Heart Rate (HR)
Rationale: Phentermine can cause tachycardia and palpitations.
Timing: Prior to initiation of therapy
Weight and BMI
Rationale: To establish baseline and track efficacy.
Timing: Prior to initiation of therapy
Medical History (especially cardiovascular, psychiatric, and substance abuse)
Rationale: To identify contraindications and risk factors.
Timing: Prior to initiation of therapy
Routine Monitoring
Blood Pressure (BP)
Frequency: Regularly (e.g., weekly for first few weeks, then monthly)
Target: Maintain within acceptable limits; discontinue if sustained significant elevation occurs.
Action Threshold: Discontinue if sustained significant increase in BP or HR is observed.
Heart Rate (HR)
Frequency: Regularly (e.g., weekly for first few weeks, then monthly)
Target: Maintain within acceptable limits.
Action Threshold: Discontinue if sustained significant increase in BP or HR is observed.
Weight and BMI
Frequency: Monthly
Target: Progressive weight loss (e.g., 5% in 12 weeks)
Action Threshold: Consider discontinuation if insufficient weight loss (e.g., <3% in 12 weeks) or if weight loss plateaus.
Signs/Symptoms of Pulmonary Hypertension (e.g., dyspnea, angina pectoris, syncope, lower extremity edema)
Frequency: At each visit
Target: Absence of symptoms
Action Threshold: Discontinue immediately if symptoms develop.
CNS and Psychiatric Symptoms (e.g., insomnia, nervousness, agitation, mood changes, signs of dependence)
Frequency: At each visit
Target: Absence of severe or worsening symptoms
Action Threshold: Adjust dose or discontinue if severe or intolerable symptoms occur.
Symptom Monitoring
- Chest pain
- Shortness of breath (dyspnea)
- Fainting (syncope)
- Swelling in legs/ankles (edema)
- Palpitations
- Dizziness
- Insomnia
- Nervousness
- Agitation
- Tremor
- Dry mouth
- Constipation
- Changes in mood or behavior
Special Patient Groups
Pregnancy
Contraindicated during pregnancy (Pregnancy Category X). Weight loss during pregnancy offers no benefit to the pregnant woman and may result in fetal harm. Phentermine is not indicated for use in pregnancy.
Trimester-Specific Risks:
First Trimester:
Potential for fetal harm; studies in animals have shown adverse effects.
Second Trimester:
Not recommended; no known benefits for weight loss during pregnancy.
Third Trimester:
Not recommended; no known benefits for weight loss during pregnancy.
Lactation
Contraindicated during breastfeeding (Lactation Risk L5). 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 risk of adverse effects; avoid use.
Pediatric Use
Contraindicated in children under 16 years of age due to lack of established safety and efficacy. Use in adolescents (16-18 years) should be approached with extreme caution and only if potential benefits outweigh risks, under strict medical supervision.
Geriatric Use
Use with caution in elderly patients (65 years and older). Start with the lowest effective dose (e.g., 15 mg daily) due to the greater frequency of decreased hepatic, renal, or cardiac function, and concomitant disease or other drug therapy. Monitor closely for cardiovascular and CNS adverse effects.
Clinical Information
Clinical Pearls
- Phentermine is indicated for short-term use only (typically a few weeks) as an adjunct to a comprehensive weight management program.
- Tolerance to the anorectic effect may develop within a few weeks; increasing the dose is not recommended due to increased risk of adverse effects.
- Patients should be advised about the potential for dependence and withdrawal symptoms upon abrupt discontinuation after prolonged use.
- Careful cardiovascular monitoring (BP, HR) is crucial, especially in patients with pre-existing cardiovascular risk factors.
- Educate patients on the importance of lifestyle modifications (diet, exercise) as the cornerstone of weight management, as phentermine is only a temporary aid.
- Avoid late evening dosing to prevent insomnia.
Alternative Therapies
- Liraglutide (Saxenda)
- Semaglutide (Wegovy)
- Naltrexone/Bupropion (Contrave)
- Orlistat (Xenical, Alli)
- Setmelanotide (Imcivree - for specific genetic conditions)
- Other lifestyle interventions (diet, exercise, behavioral therapy)
Cost & Coverage
Average Cost:
Varies widely, typically $20-$100+ per 30 tablets
Generic Available:
Yes
Insurance Coverage:
Often Tier 3 or 4, or may not be covered by some plans as a weight loss medication. Coverage varies significantly by insurer and plan.
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 details. If you have any questions or concerns about this medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider for clarification. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide information about the medication taken, the amount, and the time it happened, as this will aid in your care.