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Key takeaways
Cialis and Viagra have several potential side effects in common, including headaches, nasal congestion, and skin flushing.
Cialis is more likely to cause serious back pain or muscle pain than Viagra, and Viagra is more likely to cause vision changes.
Cialis side effects come on more slowly, but can last longer than Viagra side effects.
If you are receiving medication for erectile dysfunction (ED), you will likely be prescribed a drug like Cialis or Viagra. Both are in a class of medications called phosphodiesterase (PDE) inhibitors. They work by increasing blood flow to the penis. Cialis is the brand name for tadalafil and is FDA-approved to treat erectile dysfunction and benign prostatic hyperplasia (BPH) or enlarged prostate. Viagra is the brand name for sildenafil, but it is only FDA-approved as an ED treatment.
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Common side effects of Cialis vs. Viagra
Like all medications, Cialis and Viagra can cause side effects. Above all, the most common side effect of both medications is headaches. For example, according to clinical data, between 16-28% of people experience headaches when taking Viagra, depending on dosage. Likewise, 3-16% of people taking Cialis experience headaches, depending on the dose and formulation of the medication they are taking.
Headaches are common to both Cialis and Viagra because both drugs work by making blood vessels dilate in the body, which can also impact blood vessels in the brain. “Most of the time, this makes a dull, mild pain that goes away on its own,” explains Menachem Jacobs, MD, co-founder of Outlive Biology and a resident physician at Yale New Haven Hospital. “For instance, a patient might take a dose and then get a mild headache an hour later, but it usually goes away in a few hours.”
According to clinical trials, both Cialis and Viagra share many of the same side effects. Side effects that both Viagra and Cialis have in common are:
- Headaches
- Flushing of skin
- Vision changes or vision loss
- Nasal congestion
- Back pain
Although the two medications share several side effects, there are also some key differences when it comes to Cialis vs Viagra side effects. “Some men experience mild back pain or muscle aches more commonly with Cialis, while Viagra is more likely to cause visual disturbances, such as a blue-tinted vision or increased light sensitivity,” explains David Shusterman, MD, urologist at Modern Urologist.
Serious side effects of Cialis vs. Viagra
While less common, both Cialis and Viagra can cause serious side effects at times. The serious side effects that both medications have in common include:
- Vision changes or vision loss
- Hearing loss
- Nervous system impacts, like seizures
- Cardiovascular events like heart attacks, chest pain, and strokes in people with pre-existing cardiac issues
A rare, but serious side effect that both medications can trigger is priapism, which is when you have a prolonged erection. “Priapism is an emergency that needs to be treated by a doctor, so a visit to the emergency room may be needed,” says George F. Ellis, MD, physician, urologic surgeon, and also a writer and filmmaker at Coronado Beach Productions.
How soon do side effects start?
One major way that Cialis vs Viagra effects differ is that Viagra tends to work faster than Cialis, but Cialis stays in the body longer than Viagra.
Viagra starts working within 30–60 minutes after taking it. “Side effects tend to appear and subside in the same time frame,” Dr. Shusterman says. On the other hand, Cialis takes about 45 to 90 minutes to work, Dr. Shusterman notes, but its full effects can last up to 36 hours. “Because of its longer half-life, mild side effects like flushing or back discomfort may linger longer but are usually less intense,” Dr. Shusterman describes.
How long do side effects last?
Viagra lasts for much less time than Cialis—about four hours, according to studies. Cialis, on the other hand, is much longer lasting, with research showing that it lasts up to 36 hours. This is due to its half-life of 17.5 hours. “A lot of the time, I tell patients that Cialis is called the ‘weekend pill’ for a reason, and this affects the side effects,” Dr. Jacobs says. According to Dr. Jacobs, Cialis side effects tend to start more slowly than Viagra side effects, but tend to last longer.
What are the long-term side effects of Cialis vs. Viagra?
Neither Cialis or Viagra have serious known long-term or permanent effects. Any long-term side effects are minimal when the medications are used appropriately and under the supervision of a doctor, according to Dr. Shusterman. “There’s no evidence that Cialis or Viagra causes dependency or lasting cardiovascular damage,” he says. “However, patients with underlying cardiac disease should always be evaluated before use.”
Cialis vs. Viagra contraindications
Most people with penises can safely take Cialis and Viagra, but there are certain individuals who should avoid them. Here’s what to know.
Underlying medical conditions
People with certain medication conditions should avoid Cialis and Viagra due to severe side effects that can be life-threatening. Cialis and Viagra should be avoided or taken with caution in people with severe heart disease, recent stroke or heart attack, or significant liver or kidney impairment, according to Dr. Shusterman.
Use in children and pregnancy
Neither Cialis nor Viagra is indicated for use in children, pregnant people, or breastfeeding parents. They haven’t been studied in these populations and should be avoided.
Use in geriatric populations
Both medications are typically used in older patients and are considered safe in the elderly population. However, it’s always important to consult with your healthcare provider before using Cialis or Viagra, especially in older age, because co-morbid medical conditions or medications you are taking might change this recommendation.
Cialis vs. Viagra warnings
Both Cialis and Viagra come with certain warnings. For example, precautions should be taken in patients with underlying cardiovascular disease because of an increased risk of heart attacks and strokes. Another major warning is about priapism, which is a prolonged erection of more than four hours. Anyone experiencing this should seek emergency medical care.
It’s possible to overdose on either Cialis or Viagra. This can happen if you take more than the prescribed amount. In the event of an overdose, call the Poison Control helpline at 1-800-222-1222 or visit the Poison Control website for assistance. Go to the nearest emergency room if you are having trouble breathing, have a seizure, have collapsed, or have fainted and can’t be woken up.
There are no current significant recalls of either Cialis or Viagra, but the FDA warns that you should stay away from sexual supplements distributed by a company called Pyramid Wholesale, because they may contain undeclared and unregulated amounts of Cialis or Viagra.
In essence, you should never take a supplement containing either of these drugs, and only commercially produced medication prescribed by a healthcare provider.
Cialis vs. Viagra interactions
Though uncommon, both Cialis and Viagra can interact poorly with certain foods and medications. Here’s what to know about Cialis and Viagra food and drug interactions.
Nitrates
Both Cialis and Viagra are contraindicated if you are taking nitrates in any form. “Neither medicine should be used by anyone who is already taking nitroglycerin or another nitrate prescription for chest discomfort,” Dr. Jacobs says. “A potentially fatal reduction in blood pressure can result from combining the two. Both drugs are subject to this stringent restriction.”
Concomitant guanylate cyclase (GC) stimulators
You should not use Viagra if you are using a GC stimulator, including Adempas (riociguat). That’s because combining Viagra and a GC stimulator can increase the low blood pressure-lowering effects of the GC stimulator.
High-fat meals
It’s not recommended that you eat fatty foods along with Viagra. “Viagra should not be taken with high-fat foods as there may be a delay or decrease in effectiveness,” Dr. Ellis says. On the other hand, Cialis is not significantly impacted by the type of food you consume.
Alcohol
It’s best to avoid or minimize the use of alcohol when taking either Cialis or Viagra. “Alcohol can amplify dizziness or lightheadedness with either,” Dr. Shusterman says. “But the effect is stronger with Cialis due to its longer duration in the bloodstream.”
How to avoid Cialis vs. Viagra side effects
There are several steps you can take to avoid or minimize both Cialis and Viagra side effects. Here are some tips from Dr. Shusterman:
- Start with lower doses of the medication and gradually increase them, if needed. This may look like 5–10 mg of Cialis or 25–50 mg of Viagra.
- Avoid excessive alcohol use.
- Avoid large, fatty meals before taking Viagra.
- For Cialis, hydration can help minimize any back discomfort.
- Taking the pills at least 30–45 minutes before anticipated sexual activity allows for a smoother onset of desire effects (erections) with fewer surprises.
- If side effects occur, consider spacing out the doses or switching to a different formulation.
How to treat side effects of Cialis vs. Viagra
You should call your healthcare provider if you are experiencing any uncomfortable side effects of taking Viagra or Cialis. Your provider can help you decide whether adjusting the dose or trying an alternative medication or treatment option is right for you.
If you are having serious side effects like vision changes, hearing loss, seizures, or cardiovascular effects, seek immediate medical attention.
Prolonged erections that last for 4 hours are also a reason to seek emergent medical attention.“An emergency department physician would usually provide a syringe and needle to remove blood from the penis as a treatment for this condition,” Dr. Jacobs describes. “They may also inject a drug that helps reduce erections by narrowing blood arteries.”
As with any medication, you should seek medical advice from a healthcare professional if you have any questions, and only take these medications under their supervision. “These are prescription medications and should be prescribed as part of treatment by a doctor who knows the patient’s medical history, including medications, allergies, and other medical conditions,” Dr. Ellis emphasizes.
- Label: Cialis– tadalafil tablet, film-coated, DailyMed (2009)
- Label: viagra– sildenafil citrate tablet, film coated, DailyMed (2017)
- Onset and duration of action of sildenafil for the treatment of erectile dysfunction, Br J Clin Pharmacol (2002)
- The role of tadalafil in treated hypertensive patients with erectile dysfunction, J Clin Hypertens (2022)
- Pyramid wholesale issues recall of various brands of products sold as dietary supplements for sexual enhancement because they contain undeclared prescription drugs, including sildenafil (viagra) and/or tadalafil (Cialis), U.S. Food and Drug Administration, FDA (2024)
- Sildenafil, MedlinePlus (2023)
- Tadalafil, MedlinePlus (2023)