Frequently Asked Questions

by Rakib Sarwar, RPh on November 22, 2018

Got a question about phentermine or phentermine alternatives (OTC)?

Click or tap on any question below to reveal the answer.

How/where can I get a phentermine prescription?

To receive a prescription for phentermine, you’ll need to follow these steps:

  1. Find a weight loss clinic (preferably near you) and call them to inquire about whether they prescribe phentermine. If yes, proceed to step 2.
  2. Schedule an in-person, face-to-face consultation with the clinic.
  3. During the consultation, you’ll receive a medical exam, have your BMI calculated, as well as answer questions for medical intake.
  4. The physician at the clinic will consider your stats and exam results, and make a decision about whether you qualify.
  5. If you qualify, the physician may write a prescription for phentermine, which you’d get filled at your local pharmacy.

What phentermine alternatives are available OTC?

For a detailed comparison of popular alternatives to phentermine, see our Phentermine Alternatives comparison chart.

These alternatives are available over the counter (OTC), meaning you don’t need a prescription to buy them. Most are available to purchase online.

What is the active ingredient of Phentermine?

The drug Phentermine contains the active ingredient “Phentermine Hydrochloride”.(1)

What dosage and dosage forms of Phentermine are available?

Phentermine is found in 15 mg, 30 mg, and 37.5 mg dosage.  Phentermine is available in the market in tablet and capsule dosage form.(1)

Who should be advised to take Phentermine?

Phentermine is generally prescribed for men and women over 18 years of age with Binge Eating Disorder or obesity combined with related complications. This supplement is often considered for those people who have a Body Mass Index  over 30. (1)

Who shouldn’t be advised take Phentermine?

Phentermine is not recommended for those people who are under the age of 16, not even carefully monitored dosages. Phentermine is usually not recommended for geriatric patients. One reason is that many elderly patients are not able to participate in an increased physical activity, making it difficult to begin an ongoing regimen for future progress. Also, many elderly require a variety of prescription medicines which may interact adversely with Phentermine.

Do not take Phentermine without a doctor’s approval if you:

  • have a history heart disease
  • have uncontrolled hypertension
  • have glaucoma
  • have an overactive thyroid
  • are taking a Monoamine Oxidase Inhibitor (MAOI) now or in the past 14 days
  • are pregnant or planning to become pregnant—could be dangerous to developing a fetus
  • are breastfeeding
  • are prone to agitation, extreme restlessness or irritability
  • have a history of drug abuse
  • suffer from kidney disease—could hasten the deterioration of kidney function 

Discuss possible insulin fluctuations if you are diabetic.  Always discuss any possible interactions with other regularly prescribed medications. Also, do not drive a car or heavy equipment until you know how taking Phentermine will affect you.(2)

How does it work?

Phentermine works in the nervous system by stimulating the release of certain chemicals that may make you feel like your stomach is full. As a result,  you will eat less. Along with curbing appetite, the drug reduces the body’s ability to absorb starch and fat, allowing them to pass through the body without being metabolized. This result in quicker weight loss than diet alone. (2)

Although some weight loss may be achieved by Phentermine alone, the best results will be achieved when combined with counseling to change harmful habits and address underlying issues associated with severe weight gain. It is recommended that this weight-loss supplement is taken for limited periods of time to avoid any possibility of addiction or serious side effects. 

Is this really effective for losing weight?

Phentermine has been well documented as an effective, safe weight-loss supplement. It is FDA approved and its safety and efficacy to the patients are well established. Phentermine is the most prescribed weight-loss drug in America and has been shown to be highly effective when combined with a healthy diet and increased physical activity.The most popular brand names prescribed are Adipex-P, Suprenza, Ionamin etc. This medication is used to meet the initial, short-term goal of a total healthy lifestyle plan.(4, 7)

What may be the benefits from Phentermine?

Phentermine is an appetite suppressant which is commonly prescribed in conjunction with diet and lifestyle therapy for those with severe obesity complicated by weight-related health issues. If it is used properly, Phentermine can help users begin to lead a more healthy lifestyle by causing quicker initial weight loss.

What diet precautions we should maintain before taking Phentermine?

Individuals who are taking Phentermine should be always careful about their dietary needs. For example, protein requirements, B-vitamins and Omega 5 and 6 fatty acids.

Will I take Phentermine only after a meal?

You can take Phentermine both before and after a meal. (1)

How long I need to continue Phentermine?

Phentermine is a short-term weight-loss medication taken for 12 weeks or less. Some states allow prescriptions of not more than one month at a time to ensure proper monitoring of the effects.(2)

What to do if I miss a dose?

If you miss a dose, take it immediately if possible. If it is almost time for your next dose, skip the dose and then continue on your regular regimen. Do not double the dose.(1)

What to do in case of an overdose?

In case of overdose, call your doctor immediately or seek emergency medical attention. You may also contact any poison control center.(1)

Is it safe for pregnant women and fetus?

Phentermine is among the Pregnancy category -X and not recommended to pregnant women. It may affect the fetus gaining required weight. (1)

Is it safe for lactating mothers?

Lactating mothers shouldn’t take Phentermine to ensure the safety of the infant. The potential side effects of the drug may affect the baby. (1)

Is it applicable for pediatric patients?

The obesity in Pediatric patients is a chronic condition and requires long-term treatment. There is no proven evidence of the effectiveness of this drug in Pediatric patients as this drug is used for short-term treatment.

Is it suitable for geriatric patients?

Phentermine is usually not recommended for geriatric patients. One reason is that many elderly patients are not able to participate in an increased physical activity, making it difficult to begin an ongoing regimen for future progress. Also, many elderly require a variety of prescription medicines which may interact adversely with Phentermine.

What is the difference between Phentermine tablet and Phentermine capsule?

Phentermine is manufactured in both tablet and capsule form. Capsules are generally easier to swallow and absorbed more quickly, though some are designed for extended release. Tablets are available in smaller dosages or may be divided if needed.

What are the differences between yellow and blue capsules of Phentermine?

Capsules may be one of two colors, yellow or blue. Both colors contain the same dosage of Phentermine. The difference in inactive ingredients is the reason for the different colors. Yellow is always a generic brand resin. Blue may be either a name brand or generic. Color does not affect the effectiveness of the primary ingredient.

Can I purchase Phentermine without a prescription?

Phentermine is a prescription product. You can get prescriptions from a doctor or from some weight control clinics. Purchasing Phentermine without prescription is illegal in the United States.  But some online Pharmacies may allow Phentermine without prescription. But, it is strongly recommended not to purchase without a prescription.

Is there any chance of abuse?

Phentermine has  a class IV controlled substance. So there is a chance of physical and psychological dependence. Besides these, it has a number of side effects. This is why it is not available over the counter.(2)

Is there any adverse action of Phentermine with other medications?

Phentermine may affect how other medications work in your body or vice versa. Also, combining this medication with others may also increase or worsen potential side effects. Avoid taking any other OTC weight-loss drugs while taking Phentermine.

Consult your doctor before taking Phentermine if you are taking:

  • MAOIs for depression
  • Adrenergic neuron blocking drugs to control high blood pressure or psychotic symptoms[2]
  • Selective serotonin reuptake inhibitors (SSRIs) for the treatment of depression or anxiety

What are the side effects of Phentermine?

The most common side effects of Phentermine are:

  • Dry mouth
  • Restlessness
  • Difficulty sleeping—usually occurs in the first week and then goes away
  • Increased heart rate/blood pressure
  • Stomach upset such as either constipation or diarrhea
  • Itchy skin (2)

How to overcome the Phentermine side effects?

If you experience itching which worsens or a severe rash appears, discontinue use and consult your doctor. Also, if you have ongoing problems with insomnia you should seek professional counsel about dosage adjustments or alternatives.

More serious side effects sometimes occur. Most can be avoided by a limited regimen and strict dosage control of the weight-loss medication. Ongoing studies indicate that these side effects are rare with short-term usage.

Does it affect the period of women?

Women taking Phentermine have sometimes experienced irregular or sporadic monthly cycles, spotting, or worsening symptoms such as cramps or PMS. If you already experience problems in this area, Phentermine may not be a good choice for you. (1)

Is Phentermine suitable for both men and women?

Yes, Phentermine is suitable for both men and women. But, it may affect the monthly cycle of women. The women who are already suffering from menstrual problems should avoid this drug. (1)

Is Phentermine suitable for vegetarians?

Vegetarian food habit or other diet choices will not negatively affect the use of this medication.

Where to buy Phentermine?

Phentermine is available in all the pharmacies and drug stores in the United States. It is also available in online shops or drug stores. Some online shops offer even overnight shipment.

Where can I get Phentermine cheaply?

Online purchases are cheaper in bulk, so if you know how long you will be taking Phentermine, you should order the full amount if possible.

Is there any alternative drug of Phentermine?

Yes. If the patient has any issue with Phentermine, there are several drugs which Physicians may suggest as an alternative to the drug Phentermine. Such as Benzphetamine, Liraglutide, Lorcaserin, Diethylpropion, Phendimetrazine etc. There are also some over the counter pills available in the market.

Why Phentermine is prescribed along with Topiramate?

Phentermine is often prescribed with Topiramate, in either a combined form or separately. Topiramate came to the market as a seizure medication or as a treatment for migraines. However, it was found that many patients also experienced weight loss while taking this medication. It has been found that Topiramate is helpful in treating obesity-related to diabetes, high blood pressure or high cholesterol.(6,8)

Is Phentermine safe for cardiac patients?

If anyone who suffers from cardiac problem should regularly monitor the effects for any potential complications.(3) Some of the more serious side effects could include:

  • Primary Pulmonary Hypertension—a rare but fatal disease of the lungs. Stop taking Phentermine and seek medical attention if you have difficulty breathing, severe chest pain, feel faint or nauseated, or experience swelling in the legs and feet.
  • Heart valve disease

Is Phentermine suitable for diabetic patients?

Diabetic patients may experience Low blood sugar (hypoglycemia) due to Phentermine. Keep careful track of your blood sugar level if you are diabetic patient and adjust your drug doses accordingly discussing with your physician.(5)

Is it suitable for the people who have insomnia problem?

If you have ongoing problems with insomnia you should seek professional counsel about dosage adjustments or alternatives. (1)

Can Phentermine cause harm to the Kidneys?

The individuals who are suffering from kidney disease should avoid Phentermine.  Phentermine could hasten the deterioration of kidney function. (1)

Can I drink alcohol during Phentermine treatment?

Alcohol should be avoided while taking Phentermine. It may increase the risk of side effects, especially stomach problems such as diarrhea. Alcohol also dulls the nervous system, which may negate the full effects of the medication. Discontinue alcohol intake at least 4 days before beginning a Phentermine regimen. (1)

Can phentermine affect skin?

If you experience itching which worsens or a severe rash appears, discontinue use and consult your doctor.

Which brands I should buy?

The most popular brand names prescribed are Adipex-P, Suprenza, Ionamin etc.

Does the generic drug work the same?

Active ingredients of both the generics and brands are the same. Different pharmaceuticals use different inactive ingredients to create a unique pill. The bio-equivalence of both the generic and the brands are similar. Some people may feel better on the brands due to other reasons but the efficacy of the active ingredient is the same. The generics are found cheaper than the brands as it involves lesser costs.

How to achieve the best results from Phentermine?

To achieve the best results it needs combined effort of the medication, diet and lifestyle therapy. It is also recommended to monitor it’s effectiveness and dosage adjustment under supervision of a professional or a doctor.

Can Phentermine cause positive result in drug test?

Yes. There is a chance of getting a false positive result for amphetamine as it has amphetamine-like structure.

Can I take this drug with other weight loss drugs?

Doctors usually don’t recommend the co-administration of Phentermine with other similar drugs to lose weight.(1)