Phentermine Hydrochloride
Pronunciation: (fen-TER-meen).
- Generic name
- Phentermine hydrochloride
- Brand names
- Apo-Phentermine, Adipex, Adipex-P, Phentermine, Lomaira, Ponderal
- Drug class
- Anorectic (Centrally Acting Appetite Suppressant)
Availability and supply rules vary by country
Trade names by country: United States
Australia: · Full directory
What Phentermine hydrochloride is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how Phentermine hydrochloride works
Phentermine is a sympathomimetic amine that acts as an appetite suppressant. It stimulates the release of norepinephrine in the hypothalamus, leading to reduced hunger perception. It may also increase levels of dopamine and serotonin to a lesser extent, contributing to appetite suppression. (2)
What Phentermine hydrochloride is used for
Short-term adjunct (a few weeks) to diet, exercise, and behavioral modification for weight reduction in exogenous obesity
FDA-indicated for patients with an initial body mass index ≥30 kg/m², or ≥27 kg/m² in the presence of other risk factors (e.g. controlled hypertension, diabetes, hyperlipidemia). (2)
Before taking Phentermine hydrochloride
Do not take / not appropriate for
- : advanced arteriosclerosis, symptomatic cardiovascular disease, moderate to severe hypertension, hyperthyroidism, glaucoma, agitated states, history of drug abuse, and use during pregnancy or breastfeeding. (Contraindication) (2)
Tell your clinician about
(2)How to take Phentermine hydrochloride
- General Instructions: Take phentermine exactly as prescribed by your doctor. Do not take larger or smaller amounts or for longer than recommended.. Adult Dosing: Typical adult dose: 15 mg to 37.5 mg once daily, taken before breakfast or 1-2 hours after breakfast. Dosage may be adjusted based on response and tolerability.. Pediatric Dosing: Phentermine is not recommended for children under 16 years of age.. Administration: Take the medication in the morning to avoid insomnia. Swallow tablets or capsules whole with water. Do not crush or chew.. When To Seek Review: Seek prompt medical advice if you experience serious side effects, chest pain, or shortness of breath, or if you have not lost at least 5% of your baseline body weight after 12 weeks; let your doctor advise whether to continue or stop phentermine.. Storage: Store at room temperature (20–25°C/68–77°F), away from moisture and heat. Keep out of reach of children.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (2)
Missed dose
If you miss a dose, take it as soon as you remember in the morning. If it is late in the day, skip the missed dose and resume your regular schedule the next day. Do not take an extra dose to catch up.
Overdose
Symptoms of overdose may include restlessness, tremor, rapid breathing, confusion, hallucinations, panic, aggressiveness, nausea, vomiting, diarrhea, irregular heartbeat, or seizures. Seek emergency medical attention or call your local poison control center immediately. (2)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Dry mouth, unpleasant taste, diarrhea, or constipation
Incidence: Reported in FDA prescribing information; frequency not quantified
Overstimulation, restlessness, insomnia, dizziness, tremor, or headache
Incidence: Reported in FDA prescribing information; frequency not quantified
Palpitations, tachycardia, or elevated blood pressure
Incidence: Reported in FDA prescribing information; frequency not quantified
Shortness of breath, chest pain, fainting, or leg swelling (possible signs of pulmonary hypertension or heart valve problems)
Incidence: Rare but serious; described in FDA Warnings and Precautions
Serious warnings
Not for use in pregnancy or breastfeeding — serious
Symptoms: Not for use in pregnancy or breastfeeding. May increase blood pressure and heart rate. Risk of dependence or abuse. May worsen mental health conditions. Not recommended for long-term use.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
FDA WARNINGS AND PRECAUTIONS (found missing from this page during the 2026-08-07 research pass) — serious
Symptoms: FDA WARNINGS AND PRECAUTIONS (found missing from this page during the 2026-08-07 research pass): primary pulmonary hypertension and/or regurgitant cardiac valvular disease have been reported with anorectic agents, including phentermine. Phentermine should be discontinued, on medical advice, in the event of new, unexplained shortness of breath, chest pain (angina), fainting (syncope), or lower-extremity swelling. Report any of these symptoms to a healthcare provider promptly.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Contraindications recorded in the clinician database — serious
Symptoms: Contraindications recorded in the clinician database: Contraindications include: advanced arteriosclerosis, symptomatic cardiovascular disease, moderate to severe hypertension, hyperthyroidism, glaucoma, agitated states, history of drug abuse, and use during pregnancy or breastfeeding. Use with caution in patients with mild hypertension, diabetes, renal impairment, or psychiatric disorders.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Phentermine may interact with other medications, including monoamine oxidase inhibitors (MAOIs), other stimulants, certain antidepressants, and some blood pressure medications. Combining phentermine with other weight loss drugs can increase the risk of serious side effects such as pulmonary hypertension. Always inform your healthcare provider about all medicines and supplements you are taking. | (2) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Phentermine is FDA Pregnancy Category X — contraindicated in pregnancy. Weight loss offers no potential benefit to a pregnant woman and may cause fetal harm; a minimum weight gain (no weight loss) is recommended for all pregnant women, including those who are overweight or obese. If a patient becomes pregnant while taking phentermine, the medication should be stopped and the prescriber informed promptly. (2)
Breastfeeding
The FDA label reviewed for this page does not provide lactation data for phentermine; the clinician-authored record advises against use during breastfeeding. Discuss with your healthcare provider. (2)
Children
Frequency: Not applicable. Weight Based: Not recommended for pediatric use. Max Daily Dose: Not applicable. Max Single Dose: Not applicable. Age Restrictions: Safety not established in children (2)
Renal_impairment
Renal: the FDA label states phentermine is substantially excreted by the kidney, and the dose should be limited to 15 mg daily in patients with severe renal impairment (eGFR 15-29 mL/min/1.73m²); risk of toxic reactions may be greater with impaired renal function. Hepatic: the FDA label reviewed for this page gives no specific hepatic-impairment dose adjustment; hepatic status should be assessed by the prescriber. (2)
Hepatic_impairment
Renal: the FDA label states phentermine is substantially excreted by the kidney, and the dose should be limited to 15 mg daily in patients with severe renal impairment (eGFR 15-29 mL/min/1.73m²); risk of toxic reactions may be greater with impaired renal function. Hepatic: the FDA label reviewed for this page gives no specific hepatic-impairment dose adjustment; hepatic status should be assessed by the prescriber. (2)
Monitoring
(2)Storage
The FDA label reviewed for this page directs storage at 20-25°C (68-77°F), with excursions permitted to 15-30°C (59-86°F) (USP Controlled Room Temperature), dispensed in a tight, light-resistant, child-resistant container.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Exogenous obesity (short-term adjunct to weight reduction)
Dose summary: Usual adult dose: 37.5 mg once daily before breakfast or 1-2 hours after breakfast (some patients may need only 18.75 mg daily, or 18.75 mg twice daily); individualize to the lowest effective dose. Not recommended in children under 16.
Renal context: The FDA label states phentermine is substantially excreted by the kidney; limit the dosage to 15 mg daily in patients with severe renal impairment (eGFR 15-29 mL/min/1.73m²). The risk of toxic reactions may be greater in patients with impaired renal function. (2)
Hepatic guidance
The FDA label reviewed for this page gives no specific hepatic-impairment dose adjustment for phentermine. Hepatic status (along with renal and cardiac function) should be considered by the prescriber, as underlying disease or concomitant therapy can affect the risk of toxic reactions.
Frequently asked questions
How long can I take phentermine?
Phentermine is generally prescribed for short-term use, typically up to 12 weeks. Long-term safety and effectiveness have not been established.
Can I drink coffee or caffeinated drinks while on phentermine?
Caffeine can increase the risk of side effects such as nervousness, palpitations, and insomnia. Limit caffeine intake while taking phentermine.
Is phentermine addictive?
Phentermine has the potential for abuse and dependence, especially in individuals with a history of substance misuse. Use only as directed by your doctor.
Can I take phentermine with other weight loss medications?
Combining phentermine with other weight loss drugs is not recommended due to the risk of serious side effects, including pulmonary hypertension.
What should I do if I experience chest pain or shortness of breath?
Seek immediate medical attention if you experience chest pain, shortness of breath, or other serious symptoms; let the healthcare provider you contact advise on whether to continue or stop phentermine.
Will I regain weight after stopping phentermine?
Weight regain is possible if lifestyle changes are not maintained. Phentermine should be part of a comprehensive weight management plan including diet and exercise.
Is phentermine safe during pregnancy or breastfeeding?
No. Phentermine should not be used during pregnancy or breastfeeding due to potential harm to the baby.
What happens if I take too much Phentermine?
Taking too much Phentermine can lead to serious overdose symptoms such as restlessness, tremors, rapid breathing, confusion, hallucinations, and cardiovascular events like irregular heartbeat or high blood pressure. In severe cases, it can be life-threatening. If you suspect an overdose, seek immediate emergency medical attention or call poison control.
Can I drink alcohol while taking Phentermine?
It is strongly advised to avoid alcohol consumption while taking Phentermine. Both Phentermine and alcohol can affect the central nervous system, and combining them can intensify side effects such as dizziness, drowsiness, and impaired judgment. This combination can also increase the risk of cardiovascular adverse events and may reduce the effectiveness of the medication.
Is Phentermine safe during pregnancy?
Phentermine is generally not recommended during pregnancy. It falls under a pregnancy category that suggests potential risks to the fetus, though specific human data may be limited. It is crucial to consult your healthcare provider immediately if you are pregnant, planning to become pregnant, or breastfeeding, to discuss the risks and alternative options.
What is the mechanism of action of Phentermine hydrochloride?
Phentermine is a sympathomimetic amine that acts as an appetite suppressant. It stimulates the release of norepinephrine in the hypothalamus, leading to reduced hunger perception. It may also increase levels of dopamine and serotonin to a lesser extent, contributing to appetite suppression. (2)
What is the generic name of Phentermine Hydrochloride?
The generic name is Phentermine hydrochloride. It is sold under brand names including Apo-Phentermine, Adipex, Adipex-P, Phentermine, Lomaira, Ponderal.
What class of drug is Phentermine hydrochloride?
Phentermine Hydrochloride is classed as: Anorectic (Centrally Acting Appetite Suppressant).
References
- Phentermine clinician-authored medicine recordMedGuideGlobal · International · accessed 2026-08-07 · source 1
- Phentermine Hydrochloride Tablet, USP — Prescribing Information (DailyMed)U.S. Food and Drug Administration · United States · accessed 2026-08-07 · source 2
- Phentermine — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 3
- Phentermine Hydrochloride — FDA approval record (Drugs@FDA ANDA040526)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- Phentermine — RxNorm normalized drug concept (RXCUI 8152)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient Phentermine hydrochloride names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- LOMAIRA8 mg · calvin scott & co., inc.
- Phentermine HCL C-IV37.5 mg, 15 mg · direct_rx