Tadalafil and Colestyramine: Can They Be Taken Together?

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Tadalafil and Colestyramine: Understanding the Interaction

Published: 19 October 2026

If you're prescribed tadalafil and colestyramine, you may wonder whether it's safe to take them together. The good news is that no major interaction is commonly reported between tadalafil (a medicine for erectile dysfunction) and colestyramine (a cholesterol-lowering medicine). However, colestyramine can reduce the absorption of many medicines, so timing and monitoring are important.

What is tadalafil and colestyramine used for?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you're sexually aroused [3][4]. Tadalafil is available as an on-demand treatment (10 mg or 20 mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5 mg or 5 mg). It requires sexual stimulation to work and does not increase desire on its own.

Colestyramine is a bile acid sequestrant used to lower cholesterol levels in the blood. It works in the gut by binding to bile acids, which contain cholesterol, and removing them from the body. This forces the liver to use more cholesterol to make new bile acids, thereby reducing the amount of cholesterol circulating in your blood. Colestyramine is typically prescribed for people with high cholesterol who need additional help beyond diet and lifestyle changes, or for certain other conditions such as bile acid diarrhoea.

How do tadalafil and colestyramine interact?

Colestyramine can reduce the absorption of many medicines because it binds to them in the gut, preventing them from entering the bloodstream effectively. While there is no well-documented major interaction specifically between tadalafil and colestyramine in standard references, the potential for reduced tadalafil absorption exists in theory [4][12]. This means that if you take both medicines at the same time, the colestyramine might reduce how much tadalafil your body absorbs, potentially making the ED treatment less effective.

The interaction is not considered dangerous or contraindicated—there is no risk of a serious drop in blood pressure or other acute harm from combining these two medicines. Instead, the concern is one of reduced effectiveness. Your prescriber and pharmacist will review your full medication list during your consultation to ensure that the timing of your doses is optimised and that tadalafil is likely to work as intended for you.

The mechanism in plain English

Think of colestyramine as a sponge in your gut that soaks up bile acids and cholesterol. Unfortunately, it can also soak up other medicines if they're present at the same time. Tadalafil needs to be absorbed through the wall of your gut into your bloodstream to reach the blood vessels in your penis and help with erections. If colestyramine binds to tadalafil before it can be absorbed, less of the medicine gets into your system, and it may not work as well.

What does your prescriber check before prescribing tadalafil and colestyramine together?

When you request tadalafil through an online consultation at Cured Pharmacy, you'll be asked to list all your current medicines, including colestyramine and any other cholesterol or heart medicines. The prescriber will review your medical history to ensure that tadalafil is safe and suitable for you [2][4]. They will check for any contraindications, such as recent heart attack or stroke, unstable angina, very low blood pressure, or use of nitrates, nicorandil, or riociguat (which must never be taken with tadalafil because of the risk of a dangerous drop in blood pressure).

The prescriber will also consider whether you're taking any other medicines that could interact with tadalafil, such as alpha-blockers for prostate symptoms (which can cause dizziness when combined with PDE5 inhibitors) or potent CYP3A4 inhibitors like ritonavir or ketoconazole (which can raise tadalafil levels). If you're on colestyramine, the prescriber may advise you on the best timing for taking your doses to minimise any reduction in tadalafil absorption. They will also ensure that sexual activity is safe for you, particularly if you have heart disease or other cardiovascular conditions.

Practical advice for taking tadalafil and colestyramine safely

The most important step is to separate the doses of tadalafil and colestyramine. A common recommendation is to take tadalafil at least one hour before or four to six hours after your colestyramine dose [12]. This gives the tadalafil time to be absorbed before the colestyramine enters your gut, or allows the colestyramine to pass through before you take the tadalafil. Your prescriber or pharmacist will give you specific advice based on your dosing schedule.

If you're using on-demand tadalafil (10 mg or 20 mg), plan ahead so that you can time your dose appropriately around your colestyramine. For example, if you take colestyramine in the morning, you might take tadalafil in the late afternoon or evening, well away from the cholesterol medicine. If you're on daily tadalafil (2.5 mg or 5 mg), try to establish a routine where the two medicines are taken at different times each day. Keep a note of when you take each medicine to help you remember and to discuss with your healthcare team if needed.

What if tadalafil doesn't seem to be working?

If you find that tadalafil is not as effective as expected, and you're taking colestyramine, the timing of your doses may be the issue. Speak to your prescriber or pharmacist—they may suggest adjusting the interval between doses or reviewing your overall treatment plan. Other factors can also affect how well tadalafil works, including heavy alcohol intake, a large meal before taking the tablet, anxiety, or the underlying cause of your ED. Never increase your dose without medical advice, and do not stop taking colestyramine or any other prescribed medicine without consulting your doctor first.

Are there any warning signs to watch for with tadalafil and colestyramine?

Because the interaction between tadalafil and colestyramine is primarily about reduced absorption rather than a dangerous reaction, there are no specific warning signs unique to this combination. However, you should always be alert to the general side effects and warning signs associated with tadalafil [4]. Common side effects include headache, indigestion, back pain, muscle aches, flushing, and a blocked or runny nose. These are usually mild and temporary.

Seek urgent medical help if you experience an erection lasting more than four hours (priapism), sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing. If you develop chest pain during or after sex, do not use nitrate medicines (such as GTN spray) to treat it—tell the doctor or paramedic that you have taken tadalafil, as nitrates and tadalafil together can cause a severe drop in blood pressure. If you feel dizzy, faint, or unusually unwell after taking tadalafil, especially if you're also on blood pressure or heart medicines, sit or lie down and seek advice.

Can you take other ED medicines with colestyramine?

The same principles apply to other PDE5 inhibitors used for erectile dysfunction, such as sildenafil (Viagra), vardenafil (Levitra), and avanafil (Spedra). Colestyramine may theoretically reduce the absorption of any of these medicines if taken at the same time [3][5][6]. The advice is to separate doses by at least one hour before or several hours after colestyramine, just as with tadalafil. Your prescriber will review your full medication list during the consultation and advise on timing.

Never take more than one PDE5 inhibitor at the same time—for example, do not combine tadalafil with sildenafil or any other ED medicine, as this increases the risk of side effects and low blood pressure. If you're considering switching from one ED medicine to another, discuss this with your prescriber. All PDE5 inhibitors are contraindicated with nitrates, nicorandil, riociguat, and poppers, regardless of whether you're taking colestyramine. If you're on other cholesterol medicines such as statins or ezetimibe, these do not usually interact with tadalafil in the same way as colestyramine, but always declare them in your consultation.

What about other bile acid sequestrants?

Colestyramine is not the only bile acid sequestrant. Colesevelam and colestipol work in a similar way and may also reduce the absorption of tadalafil and other medicines. If you're taking any of these, the same advice applies: separate your doses to minimise the interaction. Your prescriber and pharmacist will check your medication list and provide tailored guidance. Do not assume that because one medicine is safe with tadalafil, all medicines in the same class will behave identically—always disclose everything you're taking.

Scientific References

1. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 19 October 2026]
2. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 19 October 2026]
3. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 19 October 2026]
4. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 19 October 2026]
5. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 19 October 2026]
6. Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 19 October 2026]
7. NHS. (n.d.). Erectile dysfunction (impotence). https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ Accessed 19 October 2026.

Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.

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