Tadalafil and Dimethyl Fumarate: Can You Take Them Together?

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Key takeaways

• No major direct interaction is reported between tadalafil and dimethyl fumarate in clinical practice.
• Your prescriber reviews all your medicines and health conditions to ensure tadalafil is safe for you.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers due to dangerous blood pressure drops.
• Seek urgent help for erections lasting over four hours or sudden vision or hearing loss.
• Erectile dysfunction is common in MS and treatable; online consultation available at Cured Pharmacy.

What is tadalafil and dimethyl fumarate used for?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men [3][4]. 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 are sexually aroused. Tadalafil is the active ingredient in Cialis and is available in on-demand doses (10mg or 20mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose option (2.5mg or 5mg) [4].

Dimethyl fumarate is an immunomodulating medicine licensed in the UK for the treatment of relapsing-remitting multiple sclerosis (MS). It works by reducing inflammation in the central nervous system and may help slow the progression of disability and reduce the frequency of relapses. Dimethyl fumarate is taken orally, usually twice daily, and is an important part of long-term MS management for many people.

Erectile dysfunction can affect men with MS for various reasons, including nerve damage, fatigue, medication side effects, or the psychological impact of living with a chronic condition [1]. Treating ED can significantly improve quality of life and intimate relationships, which is why understanding how tadalafil interacts with your MS treatment is so important.

Is there an interaction between tadalafil and dimethyl fumarate?

Based on current evidence and clinical experience, there is no major direct pharmacological interaction between tadalafil and dimethyl fumarate. These medicines work through completely different mechanisms in different parts of the body: tadalafil acts on blood vessels primarily in the penis, while dimethyl fumarate modulates immune responses in the central nervous system. They are not known to interfere with each other's metabolism or effectiveness.

However, 'no major interaction' does not automatically mean the combination is suitable for everyone. Your prescriber must still assess your overall health, including your MS, cardiovascular fitness, blood pressure, and any other medicines or supplements you take. Some men with MS may have other health conditions or take additional medications that could affect whether tadalafil is safe for them [2].

During your online consultation at Cured Pharmacy, you will be asked to list all your current medicines, including dimethyl fumarate. A UK-registered prescriber will review your answers to check for any contraindications or cautions. This personalised review is essential because safe prescribing depends on your complete medical picture, not just one interaction in isolation.

What does your prescriber check when you take tadalafil and dimethyl fumarate?

When you request tadalafil while taking dimethyl fumarate, your prescriber will focus on several key areas. First, they will confirm that sexual activity itself is safe for you. Tadalafil is not suitable if you have had a recent heart attack or stroke, unstable angina, severe heart failure, or very low blood pressure [3][4]. Some people with MS may have cardiovascular issues or reduced mobility that need to be considered.

Your prescriber will also check for any medicines that do interact dangerously with tadalafil. You must never take tadalafil with nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, or recreational drugs called 'poppers' (amyl or alkyl nitrites), as this combination can cause a life-threatening drop in blood pressure [3][4]. If you take alpha-blockers for urinary symptoms (common in MS), your prescriber will ensure you are stable on that medicine and may start you on a lower dose of tadalafil.

Finally, your prescriber will review any other medications you take alongside dimethyl fumarate. Some MS treatments or medicines for related symptoms could have their own interactions with tadalafil. The consultation process ensures that every medicine you take is accounted for, so you can use tadalafil safely and effectively.

Medicines that affect tadalafil levels

Certain medicines can increase or decrease the level of tadalafil in your blood by affecting how your liver breaks it down. Potent CYP3A4 inhibitors—such as ritonavir, cobicistat, ketoconazole, itraconazole, or clarithromycin—can raise tadalafil levels, meaning your prescriber may need to reduce your dose [4]. Conversely, CYP3A4 inducers like rifampicin, carbamazepine, phenytoin, or St John's wort can lower tadalafil levels and make it less effective [4]. Dimethyl fumarate is not a significant inhibitor or inducer of this enzyme, so it does not affect tadalafil levels in this way.

Practical advice for taking tadalafil with dimethyl fumarate

If your prescriber approves tadalafil, you can take it on the same day as your dimethyl fumarate doses without needing to separate them by a specific time interval. Tadalafil can be taken with or without food, though a very heavy, high-fat meal may slightly delay its effect [4]. Dimethyl fumarate is usually taken with food to reduce stomach upset, so you can continue your normal routine.

Remember that tadalafil only works when you are sexually aroused—it does not cause an automatic erection [3][4]. On-demand tadalafil (10mg or 20mg) should be taken at least 30 minutes before you plan to have sex, and its effect can last up to 36 hours, giving you flexibility. Daily tadalafil (2.5mg or 5mg) is taken once a day at the same time and allows for spontaneity, as it maintains a steady level in your body.

Avoid drinking large amounts of alcohol when using tadalafil, as alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of the medicine, increasing the risk of dizziness [3][4]. Grapefruit juice can also raise tadalafil levels and should be limited. If you experience side effects such as headache, indigestion, back pain, or flushing, these are usually mild and temporary, but discuss them with your pharmacist or prescriber if they persist.

Warning signs and when to seek help with tadalafil and dimethyl fumarate

While tadalafil is generally well tolerated, there are some rare but serious side effects that require urgent medical attention. If you develop an erection that lasts longer than four hours (priapism), you must go to A&E immediately, as this can cause permanent damage to the penis [3][4]. Priapism is a medical emergency and needs prompt treatment.

Seek urgent help if you experience sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing, which may be accompanied by ringing in the ears or dizziness [3][4]. These are very rare but serious side effects. If you develop chest pain during or after sexual activity, stop and seek medical advice—do not take nitrate medicines for chest pain if you have used tadalafil within the last 48 hours, as this combination is dangerous [3][4].

If you notice any new or worsening symptoms related to your MS, or any unexpected side effects from dimethyl fumarate, contact your MS specialist or GP. While these are unlikely to be caused by tadalafil, it is important to report any changes in your health. Your pharmacist at Cured Pharmacy is also available to answer questions about your medicines and can advise you on whether you need to see a doctor.

Common side effects of tadalafil

The most common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. These are usually mild and go away on their own. Back pain and muscle aches typically start 12 to 24 hours after taking the dose and resolve within 48 hours. If side effects are troublesome, your prescriber may adjust your dose or suggest trying a different PDE5 inhibitor, such as sildenafil or vardenafil.

Other erectile dysfunction treatments and dimethyl fumarate

If tadalafil is not suitable for you, or if you would like to try a different option, there are several other licensed ED treatments available in the UK. Sildenafil (generic Viagra) is taken about one hour before sex and lasts for around four to six hours [3]. Vardenafil (generic Levitra) works in a similar way, taken 25 to 60 minutes before sex [5]. Avanafil (Spedra) is the fastest-acting option, working in as little as 15 to 30 minutes [6]. All of these are PDE5 inhibitors and have the same key interactions and contraindications as tadalafil.

Like tadalafil, none of these PDE5 inhibitors have a major direct interaction with dimethyl fumarate, but your prescriber will still need to review your full medical history and current medicines. You must never take more than one PDE5 inhibitor at the same time, as this increases the risk of serious side effects [3][4][5][6]. If one PDE5 inhibitor does not work well for you, your prescriber can help you try a different one or adjust the dose.

For men who cannot use PDE5 inhibitors at all—for example, because they take nitrates for angina—there are alternative treatments such as alprostadil cream (Vitaros) or alprostadil injections (Caverject), which work locally rather than throughout the body [7]. A vacuum erection device is another non-drug option. Your GP or a specialist can discuss these alternatives with you if needed [2].

Why see a GP for new erectile dysfunction

If you are experiencing erectile dysfunction for the first time, it is important to see your GP for an assessment [1][2]. ED can be an early warning sign of underlying health problems such as heart disease, diabetes, high blood pressure, or high cholesterol. Your GP can arrange blood tests and checks to identify and treat any underlying causes. Treating these conditions not only improves your general health but may also improve your erectile function. Even if you choose to use an online service like Cured Pharmacy for ED treatment, an initial GP review is a sensible step.

When to get urgent help

• Erection lasting longer than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision in one or both eyes – seek urgent medical attention
• Sudden loss or decrease in hearing, possibly with ringing in the ears or dizziness
• Chest pain during or after sexual activity – stop activity and call 999; do not take nitrates
• Severe dizziness, fainting, or signs of very low blood pressure after taking tadalafil

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.