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What is Phentermine?

Phentermine (Adipex-P) is an amphetamine-like prescription drug known as a monoamine alkaloid derivative. It is a sympathomimetic stimulant, which acts as an effective appetite suppressant. If appropriately used, phentermine can help with weight loss by decreasing hunger and increasing the feeling of being full. It is commonly known as a weight-loss drug or diet pill. 

The exact method for how this medication suppresses appetite is not known. It may help increase the amount of energy used by the body or simply affect the brain.

Phentermine is a Schedule IV drug. This is usually a classification for medication with high abuse potential, though there is little evidence that this is true for phentermine.


Phentermine Statistics



Estimated number of prescriptions for phentermine in the United States.



Total drug cost of phentermine.



Out-of-pocket cost of phentermine.


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What is Phentermine Used For?

Phentermine is used primarily for weight loss and is meant to be part of an overall plan, along with proper diet and exercise. It is intended for obese individuals who have previously failed to lose weight with other diet and exercise programs. It is prescribed for up to 12 weeks.

Obesity is defined as having a body mass index (BMI) over 30. BMI values are calculated by taking a person's weight in kilograms and dividing it by the square of their height in meters.

Phentermine is not intended for people who only want to lose a few pounds.

Side Effects of Phentermine

Phentermine is generally considered a safe and effective drug to help with weight loss for clinically obese individuals. However, there are still possible side effects that might be experienced when taking this medication. 

Common side effects are mild and include:

  • Elevated heart rate
  • Tingling in the hands or feet
  • Dry mouth
  • Sleeplessness
  • Nervousness
  • Constipation
  • Hyperactivity
  • Excitement
  • Headache

Other less common side effects may include:

  • Blurred vision
  • Decreased sex drive
  • Diarrhea
  • Gastrointestinal discomfort
  • Pain when urinating
  • Hair loss
  • Hypertension (high blood pressure)
  • Difficulty sleeping
  • Muscle pain
  • Heart palpitations
  • Tremors
  • Skin rash
  • Nausea
  • Vomiting

There is also a risk of more serious side effects when taking phentermine. These include heart valve disorders and psychotic disorders.


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Can You Drink Alcohol While Taking Phentermine?

While it is possible to drink alcohol while taking phentermine, caution should be applied if these substances are mixed. This is because alcohol has the potential to cause side effects and other problems when interacted with phentermine. 

The main issue is that alcohol can cause already present side effects to become more severe. Moreover, if these have not been experienced, mixing in alcohol can increase the risk of developing these side effects.

It is generally recommended that patients refrain from using alcohol when prescribed phentermine. Healthcare providers typically advise against the use of alcohol while taking phentermine to prevent possible harmful effects. Alcohol amplifies the effects of phentermine.

How Does Alcohol Affect Weight Loss?

While there are disputed benefits of moderate alcohol use, it can also make it more challenging to lose weight.

There is no consistently established understanding of the relationship between moderate drinking and weight loss. However, drinking more than a moderate amount of alcohol has been conclusively proven to contribute to weight gain in individuals across all health backgrounds.

There are several reasons why consuming alcohol may hinder weight loss and lead to weight gain. Alcoholic beverages typically provide hundreds of empty calories, depending on the drink, and alcohol itself contains 82 calories per ounce. Drinking alcohol to the point of intoxication also makes it easier to overeat, leading to increased fat storage.

Interestingly, alcohol also increases metabolic rate, which causes calories to be burned rather than stored as fat. However, sugar consumption also decreases when alcohol is present, meaning that more fat will be stored until the body processes the available alcohol.

Effects & Risks of Mixing Alcohol and Phentermine

There are several risks associated with mixing alcohol and phentermine. In addition to exacerbating already-present side effects, combining these substances can lead to gastrointestinal and cardiovascular problems.

Gastrointestinal effects are very common in people who drink alcohol while taking phentermine. This is mainly because alcohol irritates the stomach lining, which may cause stomach aches, heartburn, nausea, and vomiting.

The risk of cardiovascular side effects is also elevated when phentermine and alcohol are combined. Chest pain, abnormal increases in blood pressure, and an elevated heart rate may occur. In severe cases, heart failure is a possibility, though typically only if the individual has underlying medical conditions such as heart disease. 

Mixing alcohol and phentermine can also affect the central nervous system (CNS). This can lead to dizziness, drowsiness, mental depression, and concentration issues. Furthermore, mixing phentermine with other seemingly benign substances can result in harmful interactions, including ginseng, guarana, sage, and yerba mate. 


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Jordan, J., Astrup, A., Engeli, S., Narkiewicz, K., Day, W. W., & Finer, N. (2014). Cardiovascular effects of phentermine and topiramate: a new drug combination for the treatment of obesity. Journal of hypertension, 32(6), 1178–1188. https://doi.org/10.1097/HJH.0000000000000145

National Center for Biotechnology Information (2020). PubChem Compound Summary for CID 4771, Phentermine. Retrieved November 17, 2020 from https://pubchem.ncbi.nlm.nih.gov/compound/Phentermine.

Kim, K. K., Cho, H. J., Kang, H. C., Youn, B. B., & Lee, K. R. (2006). Effects on weight reduction and safety of short-term phentermine administration in Korean obese people. Yonsei medical journal, 47(5), 614–625. https://doi.org/10.3349/ymj.2006.47.5.614

Cosentino, G., Conrad, A. O., & Uwaifo, G. I. (2011). Phentermine and topiramate for the management of obesity: a review. Drug design, development and therapy, 7, 267–278. https://doi.org/10.2147/DDDT.S31443

United States Food and Drug Administration. Phentermine: Meyler's Side Effects of Drugs (Sixteenth Edition). FDA, https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/202088s005lbl.pdf

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“Phentermine.” Phentermine - Drug Usage Statistics, ClinCalc DrugStats Database, 2018, clincalc.com/DrugStats/Drugs/Phentermine.

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