Flomax And Grapefruit- Navigating A Surprising Connection

Benign prostatic hyperplasia (BPH), or enlarged prostate, affects millions of men around the globe.  The prevalence of this prostate condition increases with age. 

For example, BPH affects about 50% of men older than 50 years and is histologically evident in 90% of men by the time they turn 85 years of age.  Tamsulosin (Flomax) is a medication commonly prescribed for enlarged prostate. 

You’ve probably come across claims this medication interacts with grapefruit. Is this true? Do you need to avoid grapefruit if you’re taking Flomax? Scroll down to learn more about Tamsulosin/ Flomax and grapefruit.

The Interplay Of Flomax And Grapefruit

As noted above, grapefruit can interact with different medications and impact their effectiveness. This also includes Flomax.  Evidence shows grapefruit has an intermediate effect on tamsulosin. Side effects that may occur if you eat grapefruit while taking Flomax are postural hypotension and dizziness. 

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Grapefruit’s Impact On Blood Pressure

Postural hypotension (orthostatic hypotension) refers to when blood pressure drops when a person suddenly changes position. Hypotension is the medical name for low blood pressure.

The lower blood pressure after changing the position is what causes dizziness. Remember, you should never use this medication or a combination of the two to lower high blood pressure.

Food Sensitive Medication 

A study confirmed tamsulosin is among food-sensitive medications. Since Flomax is likely to interact with grapefruit juice and other citrus fruits, it’s important not to consume it when taking the medication. 

Otherwise, grapefruit juice could intensify the side effects of Flomax. As a result, grapefruit juice can significantly impact the effectiveness of Flomax. The effect of grapefruit on Flomax is the same as the influence of this citrus fruit on another metabolism of other medications. 

Mechanisms Behind The Interaction

More precisely, grapefruit can inhibit the CYP3A metabolizing enzyme in the small bowel wall and increase levels of medication in the blood. This is the primary route through which grapefruit acts on tamsulosin hydrochloride. 

Also, it can inhibit the OATP (organic anion transporting peptide) transporting enzyme and thereby decrease the drug’s absorption. What happens here is that eating grapefruit or drinking its juice can prevent Flomax from working properly and put you at a higher risk of developing adverse reactions. 

In addition to peripheral hypotension and dizziness, patients may also experience side effects like nausea, lack of energy, runny nose, and other cold-like symptoms. Further clinical pharmacology research is necessary to learn more about this.

The Effect Of Grapefruit On Other Medications

Although grapefruit and grapefruit juice can be refreshing, it’s best to avoid them when taking certain medications. In most cases, grapefruit juice lets more of the main active ingredient of the drug enter the blood. When the blood levels of these active compounds are high, a person is more likely to experience side effects. 

For instance, eating too much grapefruit or drinking too much grapefruit juice while taking cholesterol-lowering medications such as statins leads to a high concentration of the drug in the body. 

As a result, the risk of muscle and liver damage increases. It may also lead to kidney failure. The same problems could occur by combining this citrus fruit with blood pressure medication. This can have a major impact on blood vessels, which could lead to heart failure.

You see, the CYP3A4 enzyme in the small intestine is necessary for the metabolism of many drugs in the body. Grapefruit juice can inhibit the activity of that enzyme. This doesn’t allow the body to metabolize the drug. 

In turn, more of it enters the bloodstream and remains in the body longer. Depending on the medication, the result could be impaired heart rhythm and irregular heartbeat, which puts a person in danger of a heart attack.

At the same time, grapefruit juice can decrease the number of certain drugs in the body and thereby reduce its efficacy. Doctors and pharmacists inform patients about grapefruit drug interactions, so it’s useful to stick to their medical advice.

Foods To Avoid While Taking Flomax

Besides grapefruit, there are other things to avoid while taking Flomax. For instance, you should avoid standing for long periods or becoming overheated in hot water or during exercise. 

To prevent dizziness, you should avoid getting up too quickly from a lying or sitting position. Alcohol is also a no-no for men taking Flomax because it can increase certain side effects of the medication. To be on the safe side, the best thing to do is avoid drinking alcohol.

Grapefruit And Prostate Health- Medications Under The 

Flomax is not the only prostate medication with which grapefruit can interfere. Grapefruit juice can affect how drugs are metabolized and eliminated in the body. As a result, grapefruit can lower the effectiveness of those medications or increase the risk of adverse reactions. 

Besides angiotensin II, calcium channel blockers, high blood pressure medication, blood thinners to prevent blood clots, other drugs, and Flomax, other prostate medicines can also interact with this citrus fruit.

Other prostate medications that may interact with grapefruit include other alpha-blockers such as terazosin (Hytrin) and PDE5 inhibitors (which are also used for erectile dysfunction) such as sildenafil (Viagra). 

In cases of sildenafil, grapefruit juice can raise the levels of this medication in the body and delay the time it takes for the drug to work. As a result, your sexual activity is significantly impaired.

Also, grapefruit juice could inhibit the metabolism of other PDE5 inhibitors ED drugs such as tadalafil (Cialis Super Active), vardenafil (Levitra), and avanafil (Stendra).  Other drugs used in treating prostate conditions, such as 5-alpha reductase inhibitor finasteride (Proscar), aren’t significantly affected by grapefruit juice.

Interestingly, some theories suggest that grapefruit could interact with caffeine too, but this subject requires more research.

Alternatives To Grapefruit And Grapefruit Juice

If you take Flomax for BPH, you should avoid eating grapefruit or drinking its juice. You may also want to avoid citrus fruits in general. There are a lot of fruits and fruit juice options you can eat, though, including:

  • Peach
  • Bananas
  • Berries
  • Apples 
  • Kiwi 
  • Pomegranate and pomegranate juice

Although orange is among citrus fruits, orange juice is not expected to interact with Flomax.


Medications can interact with other drugs such as blood pressure meds and ACE inhibitors, but also with foods we eat. Like blood pressure medicine and many other medications, Flomax and grapefruit can interact. 

This citrus fruit can affect the enzyme necessary for the drug’s metabolism. As a result, the levels of the main active ingredient could increase and thereby make you more prone to side effects. 

Men who take Flomax should avoid eating grapefruit and other citrus fruits to prevent drug interaction. The best thing to do is to consult your healthcare provider regarding foods that are safe to eat.

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  1. Dunn CJ, Matheson A, Faulds DM. Tamsulosin: a review of its pharmacology and therapeutic efficacy in the management of lower urinary tract symptoms. Drugs Aging. 2002. https://pubmed.ncbi.nlm.nih.gov/11950378/
  2. Bailey DG, Dresser G, Arnold JM. Grapefruit-medication interactions: forbidden fruit or avoidable consequences?. CMAJ. 2013. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3589309/ 
  3. Paśko P, Rodacki T, Domagała-Rodacka R, Owczarek D. Interactions between medications employed in treating benign prostatic hyperplasia and food – A short review. Biomed Pharmacother. 2016. https://pubmed.ncbi.nlm.nih.gov/27551761/ 
  4. Jetter A, Kinzig-Schippers M, Walchner-Bonjean M, Hering U, Bulitta J, Schreiner P, Sörgel F, Fuhr U. Effects of grapefruit juice on the pharmacokinetics of sildenafil. Clin Pharmacol Ther. 2002. https://pubmed.ncbi.nlm.nih.gov/11823754/

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