Common Viagra and Cialis Side Effects: What to Expect and Watch For

Yes, both Viagra and Cialis can cause side effects, though most people who take them tolerate treatment well. The vast majority of reactions are mild, temporary, and predictable, with headache, flushing, and an upset stomach being the usual suspects. 

A small number of side effects are more serious and warrant immediate medical care, and it's worth knowing what those look like before you ever need to recognize one.

Do Viagra and Cialis Cause Side Effects: The Quick Answer

Both sildenafil and tadalafil can cause side effects because they increase blood flow throughout the body, not just to the area they're meant to treat. Most reactions are mild and fade on their own within a few hours. A smaller set of rare but serious effects, including priapism, sudden vision loss, and sudden hearing loss requires prompt medical attention. Knowing the difference ahead of time is the most important thing here.

Common Side Effects of Viagra and Cialis

Because both medications work by relaxing blood vessels to improve blood flow, that same effect shows up elsewhere in the body, which is where most side effects come from.

• Headache: one of the most frequently reported side effects for both medications. [1] [2]
• Facial flushing: a warm or reddish feeling in the face and neck, as blood vessels dilate.
• Nasal congestion: caused by the same vessel-relaxing effect in the nasal passages.
• Indigestion or an upset stomach: generally mild and short-lived.

In clinical data for tadalafil, headache was reported by about 11% of people on 5 mg or 10 mg doses, compared with about 15% on 20 mg. [2] A similar pattern shows up with indigestion, which climbed from about 4% at the lowest dose to 8 to 10% at higher ones. [2]

Less Common Side Effects

Some reactions show up less often but are still worth knowing about. Dizziness and back or muscle aches fall into this category for both drugs, though the two aren't identical here. 

A direct comparison of tadalafil and sildenafil found that tadalafil was associated with a meaningfully higher rate of muscle aches and back pain, likely related to how much longer it remains active in the body. [3] If you're curious how that longer window plays out more broadly, our guide to how long Viagra and Cialis last covers it in greater depth.

Vision changes are also possible, though uncommon. Blurred vision, light sensitivity, or a slight blue tinge to your vision have all been reported, generally described as mild and temporary. [1] 

These are separate from the much rarer and more serious vision event covered below, and shouldn't be confused with it.

Serious Side Effects That Need Immediate Medical Attention

A short list of reactions are more severe and require help right away. They're rare, but they're the reason a licensed healthcare provider, like the ones reviewing questionnaires through TreatMeNow, goes through your health history before prescribing either medication.

• Priapism. An erection lasting longer than 4 hours needs prompt medical attention, and one lasting past 6 hours is a medical emergency. Left untreated, it can cause permanent damage to erectile tissue. [2]
  
  
• Sudden vision loss. A rare condition called non-arteritic anterior ischemic optic neuropathy, or NAION, has been reported in people taking PDE5 inhibitors, causing sudden and sometimes permanent vision loss in one eye. [2]
  
  
• Sudden hearing loss. Cases of sudden or decreased hearing, sometimes with ringing in the ears or dizziness, have been reported after taking either medication. [1]
  
  
• Chest pain, irregular heartbeat, or symptoms of a heart attack or stroke are particularly relevant for anyone with existing cardiovascular risk factors.

If any of these happen to you, stop taking the medication and seek medical care right away.

Putting the Rare Risks in Perspective

It's easy to read a list like the one above and feel more nervous about treatment than the actual numbers support. Priapism is a good example. One analysis of drug-induced priapism cases reported to US regulators found that PDE5 inhibitors, the class that includes both Viagra and Cialis, accounted for a small fraction of cases overall, well below rates linked to some antipsychotics and other commonly prescribed medications. [4] 

That doesn't mean the risk is zero, but it does mean the numbers are a lot less alarming than the warning label alone might suggest.

NAION may also be less alarming than it seems. It's rare and more strongly associated with certain pre-existing risk factors like age, diabetes, and a specific eye structure some people are born with, and a firm causal link to PDE5 inhibitors has never been definitively established. [2]

Drug Interactions and Who Should Be Extra Careful

The most important interaction to know involves nitrate medications, often prescribed for angina or heart disease. 

Combining either drug with nitrates can cause a sudden and dangerous drop in blood pressure, which is one of the main reasons a health questionnaire is part of every online prescription. [1] 

Alpha-blockers carry a similar caution, since the combination can also lower blood pressure more than intended.

People with certain heart conditions, uncontrolled blood pressure, or a history of NAION in one eye already should discuss this in detail with their provider before starting treatment.

For more on how either medication works alongside other health conditions, our full blog on erectile dysfunction covers related topics like dosage, cost, and what causes ED in the first place.

How to Reduce Your Risk of Side Effects

A few habits can help lower how likely you are to notice side effects at all.

• Take the medication as prescribed, and let your provider guide any dose changes rather than adjusting it yourself. Our dosage guide covers the available strengths for both medications.
  
  
• Stay well hydrated, particularly if you notice headaches or flushing.
  
  
• Limit alcohol, since heavy drinking can worsen dizziness and blood pressure effects.
  
  
• Be upfront with your provider about every medication and supplement you're taking, not just the obvious ones.
  
  
• Give your body time to adjust. Many mild side effects ease up after the first few uses as you get a feel for how the medication affects you.
  
  

FAQ: What Should I Do If I Notice a Side Effect After Taking Viagra or Cialis?

Most side effects don't require any action beyond waiting them out. A headache or a flushed face after taking either medication is common, expected, and generally gone within a few hours as the drug clears your system. 

There's no need to panic over the mild, well-documented reactions covered earlier in this guide.

The exception is anything on the serious list, such as priapism, sudden vision changes, sudden hearing changes, or symptoms that feel like a cardiac event. 

Those situations call for prompt medical attention, not a wait-and-see approach, regardless of how mild or fleeting they might initially seem.

Here's a simple way to sort through it if something comes up.

1. If it's a headache, flushing, or mild stomach upset, give it a few hours. These typically resolve on their own as the medication wears off.
   
   
2. Stay hydrated and skip alcohol if you're feeling lightheaded or dizzy.
   
   
3. If you have an erection lasting more than 4 hours, treat it as urgent and seek medical care rather than waiting to see if it resolves.
   
   
4. If you notice any sudden changes in vision or hearing, stop taking the medication and get medical attention right away.
   
   
5. Mention any side effects to your provider at your next check-in, even mild ones, so they have a full picture if your prescription ever needs adjusting.