How Long After Phentermine Can I Eat (And Why)?

Exact Answer: 30 minutes

Phentermine is a commonly prescribed drug used to counter obesity. This amphetamine-like drug works by suppressing the patient’s appetite. When using the drug, the patient feels full and considerably less hungry at any given point in time.

Usually, the drug is prescribed as a part of an overall weight-loss regime and is not to be consumed singularly. A specific diet and exercise routine accompanies the intake of phentermine. The dosage and correct timing for consuming phentermine will be dependent on the doctor’s analysis of the overall health of the patient. When using the drug, it is best to stick to the physician’s dosage chart rather than self-medicating.

How Long After Phentermine Can I Eat

How Long After Phentermine Can I Eat?

When on phentermine, the rules with regard to food consumption need to be maintained because the efficacy of the drug will be dependent on its timely consumption. Doctors decide on the correct dosage and time of the medication on the basis of several health considerations of the patient. Thus, each diagnosis is different from the last.

Generally, physicians will instruct patients to take phentermine before breakfast or at least one or two hours after meals. The dosage may also be based on the consumption of the drug on an empty or semi-empty stomach. In such cases, the patient should take phentermine at least 30 minutes before meals.

When the drug is prescribed in the form of a tablet, for adults the dosage is thrice a day, 30 minutes before meals. This is the prescription when the drug is consumed in an 8mg formula. However, when phentermine is to be ingested in a 15-37.5mg form, the dosage is restricted to once a day, right before breakfast. This implies that the drug is to be taken empty stomach. It can also be taken at least 2 hours after eating. In this case, there is no time limit as to the consumption of food after the dose is ingested.


The dosage of the drug to curb obesity is based on the patient’s existing comorbidities as well as other medical conditions. Moreover, when people are on the drug, they have to monitor the kind of food they consume. Without a holistic approach to weight loss, no tangible difference can be noticed.

In summary:

Dosage FormTiming
8mg Tablets (Thrice a Day)30 minutes before meals
15-37.5mg Tablets (Once a Day)Before breakfast or at least 2 hours after meals.

Why Do You Have To Wait So Long After Phentermine To Eat?

Most medicines have certain food and drink protocols that must be stringently followed by the patient. This is to ensure that no adverse reaction to the drug occurs. Thus, patients are often asked to not consume alcohol or other intoxicating substances when on certain medications. Similarly, their diets are also closely monitored to avoid harmful interactions with the components of the drug.

In the case of phentermine, the rationale remains the same. People ingesting the drug are advised to take it on an empty stomach because the chemical components of the drug help curb the urge to eat or excess hunger when taken on an empty stomach. It helps neutralize the appetite of the patient more effectively.

Consequently, if the drug is taken right after a meal, it can hamper the outcome as well as reduce the efficacy of the chemical. Generally, patients are asked to eat after 30 minutes of ingesting phentermine because this gives the body enough time to process the chemical in the drug and thereby reduce hunger. Eating immediately after taking phentermine will undermine its efficacy as it will not be activated by the stomach acids within such a short window of time.


It is important to stick to the schedule carefully drafted by your doctor when on phentermine because there are side effects to the drug that may be aggravated when it’s stated routine consumption is disrupted. It is equally significant that the patient does not self-medicate or use the drug longer or in larger quantities than what is prescribed by the physician. This can have a cataclysmic impact on the patient’s health and well-being.


While phentermine is a drug that helps in achieving targeted weight loss, it must be taken in accordance with the orders of the doctor. This implies that phentermine’s dosage and manner of intake should remain unchanged during the course of the treatment unless a modification is indicated by the medical professional.

In order to get tangible results with phentermine, the patient must stick to a strict dietary regime that is timely planned. Usually, doctors prescribe that the drug should be taken either one or two hours after breakfast or it can be taken at least 30 minutes before meals. Again the dosage is determined by the physician and is based on several health considerations of the patient in question.


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