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Rx prescription pad and Rx pill bottle: Tamsulosin interactions
Drug Info

Tamsulosin interactions to avoid

It is important to be aware of the interactions of tamsulosin with other medications and supplements because these interactions can either decrease the effectiveness of tamsulosin or increase tamsulosin blood levels
Kristi Torres writer headshot
By | Dec. 6, 2023

Key takeaways

  • Tamsulosin is metabolized in the body primarily by the CY3A4 and CYP2D6 enzymes

  • Inhibitors of CYP3A4 and CYP2D6 will effectively increase blood levels of tamsulosin, sometimes as much as 2.5 times the intended amount of tamsulosin

  • Cimetidine, a common over-the-counter antacid sometimes known as Tagamet H, can significantly slow the excretion of tamsulosin from the body, which leads to an increased blood level.

  • The clinical effects of increased tamsulosin levels resulting from drug interactions are not fully known. However, an increased occurrence of adverse events such as headache, dizziness, low blood pressure, and abnormal ejaculation would be expected.

  • If you think you are experiencing the effects of a drug interaction while taking tamsulosin, speak to your prescriber or pharmacist for advice on how to proceed.

Drug interactions | Food interactions | Other interactions | Avoiding interactions | When to see a doctor

Tamsulosin is an oral prescription medication that belongs to a class of drugs known as alpha blockers used in the treatment of benign prostatic hyperplasia (BPH) in men, the medical term for enlarged prostate. It is a generic drug available as tamsulosin hydrochloride, and it is available under its brand name Flomax. 

Tamsulosin interacts with other prescription drugs, such as antibiotics, antifungals, and antacids. Tamsulosin should not be taken with strong inhibitors of the CYP3A4 enzyme, such as ketoconazole, or the CYP2D6 enzyme, like paroxetine. Tamsulosin and other drugs may require dosage adjustments due to concurrent effects on certain cytochrome P450 enzymes. 

It is important to be aware of the interactions of tamsulosin with other medications and supplements because these interactions can either decrease the effectiveness of tamsulosin or, conversely, increase tamsulosin blood levels beyond what is intended and considered safe. Before taking tamsulosin, ensure your prescriber is aware of all medications you are taking, both prescription and non-prescription.

Tamsulosin drug interactions

Tamsulosin interacts with drugs that have a high affinity for inhibition of CYP3A4 and CYP2D6. This includes classes of medications such as antifungals, antibiotics, antacids, and antidepressants. Phosphodiesterase-5 (PDE5) inhibitors like common erectile dysfunction drugs due to their combined tendencies to cause vasodilation and lower blood pressure. Tamsulosin is also expected to have a concomitant interactive effect from use with other alpha blockers, and duplication within this drug class should be avoided.

CYP3A4 Inhibitors

CYP3A4 inhibitors can be found across multiple drug classes. Tamsulosin depends on CYP3A4 enzymes so that it can be metabolized effectively and removed from the body. Drugs that inhibit 3A4 effectively slow or stop the metabolism of tamsulosin, leading to a build-up of the drug in your bloodstream. This can worsen normal side effects of tamsulosin, some of which are already fairly common with tamsulosin. These include headache, dizziness, rhinitis (runny nose), diarrhea, and abnormal ejaculation. If the effects of the vasodilation are too severe, fainting could occur from blood pressure being too low.

While there are many CYP3A4 inhibitors, the most notable to be concerned about is Nizoral (ketoconazole). Its inhibition of CYP3A4 is significant and should not be used with tamsulosin. If ketoconazole treatment is necessary, prescribers should consider an alternative to tamsulosin in treating BPH, such as 5-alpha reductase inhibitors (5-ARI) like Avodart (dutasteride).

Other CYP3A4 inhibitors include:

CYP2D6 Inhibitors

CYP2D6 inhibitors can also be found across multiple drug classes. The interaction is the same concept as that of CYP3A4 because tamsulosin is highly dependent on both enzymes to be metabolized. This can also lead to headache, dizziness, fainting, rhinitis, diarrhea, and abnormal ejaculation.

There are also many CYP2D6 inhibitors. These include antidepressants, anti-infectives, antimalarials, oral contraceptives, and blood pressure medications. Two common antidepressants, fluoxetine and paroxetine, are strong inhibitors of 2D6. While the concurrent use is not contraindicated, alternative therapies should be used when possible. Escitalopram has a much weaker inhibition of CYP2D6 and may be a better choice for someone requiring tamsulosin treatment.

Other CYP2D6 inhibitors include:

PDE5 Inhibitors

PDE5 inhibitors are more commonly known as erectile dysfunction drugs. They have other uses as well, such as pulmonary hypertension. The mechanism of action allows for increased blood flow to the penis during sexual stimulation. PDE5 inhibitors do not interact with tamsulosin via the CYP P450 system. Instead, the interaction lies in the combined effects of alpha blockers and PDE5 inhibitors. Both classes of drugs cause significant vasodilation. Using both together can lower blood pressure significantly and leave a patient more prone to dizziness and fainting. This can be dangerous as it can be associated with falls and other physical injuries that can be very serious. If using PDE5 inhibitors is necessary for quality of life, consider alternative BPH treatment such as a 5-ARI like Avodart (dutasteride).

Examples of PDE5 inhibitors include:

Other Alpha Blockers

Tamsulosin should not be combined with other drugs in the same class. This can cause orthostatic hypotension, dizziness, and headache. There is no evidence of clinical benefit to taking two different agents in this class.

Examples of other alpha blockers include:

Tamsulosin food interactions

Tamsulosin does not just interact with other drugs. Some dietary products can also affect tamsulosin absorption or worsen adverse events associated with tamsulosin.

Tamsulosin and grapefruit 

Grapefruit and products like grapefruit juice are strong CYP3A4 inhibitors. This will slow the metabolism of tamsulosin and increase the amount of tamsulosin in the body over time. This can increase the chance of adverse effects such as dizziness and headache.

Other than grapefruit products, tamsulosin can be taken with or without food.

Other tamsulosin interactions

Tamsulosin can interact with other substances that may be a part of your daily living. Before regularly combining these substances with tamsulosin, speak to your healthcare provider.

Tamsulosin and alcohol 

Alcohol consumption should be kept minimal for patients taking tamsulosin. The combined effect of alcohol and tamsulosin can lead to a phenomenon known as orthostatic hypotension or sudden dizziness upon standing. This can lead to stumbling, falls, and injuries.

Tamsulosin and caffeine 

Caffeine can act as a mild diuretic, and the diuretic effect can lead to some dizziness for some patients. Caffeine consumption should be kept to moderate use if you are taking tamsulosin.

Tamsulosin and sulfa allergies

While tamsulosin is a sulfonamide derivative, it is rare for patients with a sulfa allergy to have a hypersensitivity reaction to tamsulosin. Use in sulfa-allergic patients is not contraindicated, but caution should be used if you have ever had an allergic reaction to another sulfa drug. Signs of an allergic reaction include hives or trouble breathing. Contact a healthcare professional immediately if this occurs.

How to minimize tamsulosin interactions

When discussing treatment options for your BPH, ensure your prescriber is fully aware of all medications you take, even those you get over the counter. If you become ill and require antibiotic or antifungal treatment, ensure the prescriber knows you take tamsulosin. Sometimes, your healthcare provider may choose alternative therapies to avoid interactions if you have other medical conditions. While taking tamsulosin, avoid grapefruit products and limit consumption of alcohol and caffeine.

Some other important notes about taking tamsulosin

You can take tamsulosin with or without food at any time, but just make sure you are taking it at the same time each day. If tamsulosin causes drowsiness when you take it, you should not drive or operate machinery. Store tamsulosin at room temperature in a room that is not humid. If you miss a dose of tamsulosin, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose. Do not double up.

The FDA has not approved Tamsulosin for use in women and children, though at times, medical professionals may use the drug off-label in these populations for other indications.

The most common symptoms of benign prostatic hyperplasia are urgency to urinate, frequent urination at night, and difficulty beginning the process to urinate or ending the stream. The symptoms of BPH can also be similar to prostate cancer, so it is important to seek medical advice immediately if these symptoms arise. Tamsulosin could mask the signs of cancer, so physical exams are important.

Tamsolusin and other alpha blockers can increase the risk of intraoperative floppy iris syndrome (IFIS). This can increase the risk of serious adverse events during eye procedures and surgery. Be sure to tell your healthcare provider you take tamsulosin before any eye appointments or if you are experiencing eye problems. If you are scheduled for cataract surgery or any other eye procedure, wait to initiate tamsulosin therapy until that is complete.

Tamsulosin has also been associated with priapism, a persistent, painful erection not related to sexual stimulation. This must be treated immediately to avoid permanent damage to the erectile tissue. This type of adverse event should be reported to the FDA at 1-800-FDA-1088.

When to talk to a healthcare provider about tamsulosin interactions

Before starting any new medications, make sure your doctor and pharmacist are aware you are taking tamsulosin and any other prescription drugs. While the most significant interactions are listed here, there may be other interactions your healthcare provider or pharmacist needs to screen. If you start a new drug and begin to experience adverse events such as headaches, dizziness, or diarrhea, contact your prescriber immediately. If you feel faint or fall, seek help immediately.