A lot of patients ask me about the difference between the two most commonly prescribed ED meds, sildenafil (Viagra) and tadalafil (Cialis). Here we go.
WHAT DO THESE MEDS DO?
Skip this part if you’re bored by the science. Both of these meds, in addition to several other lesser-known competitors, belong to a class of drugs called phosphodiesterase-5 (PDE-5) inhibitors. These work by reducing breakdown of cyclic GMP (cGMP) within the corpora cavernosa (the spongy cylinders in the penis that fill with blood during an erection.) Cyclic GMP is the protein that causes dilation of the blood vessels within the corpora during an erection. By increasing cGMP concentration, the PDE-5 inhibitors increase blood flow and enhance rigidity while helping prevent premature loss of erection. These medications only kick in when a man is sexually aroused. This is why men on sildenafil or tadalafil don’t just walk around with a permanent erection (not counting the teenage years) as that would not be good. Arousal causes release of nitric oxide, which is responsible for activating an enzyme called guanylate cyclase, which converts guanylate triphosphate (GTP) into cGMP in the first place.
That’s a lot of info. I told you to skip that part. Cliff Notes – PDE-5 inhibitors give men better boners.
SO…VIAGRA (SILDENAFIL) OR CIALIS (TADALAFIL)?
First, its important to note that some men do better with one while others do better with the other. Additionally, the potential side effects–headache, facial flushing, heartburn, ringing in the ears etc—vary from person to person and some may experience side effects from sildenafil while others from tadalafil.
VIAGRA/SILDENAFIL
This is the grand-daddy. Viagra debuted from Pfizer in 1998 and rocked the pharmaceutical world. Viagra reps did quite well. I’m not sure why they even needed pharma reps. That stuff sold itself. Over 40,000 Viagra scripts were written in the few weeks following rollout. Sildenafil starts to work 30 to 60 minutes after being taken, and usually works for 4-8 hours (half-life in plasma of 4 hours.) Unlike tadalafil, sildenafil works best if taken on an empty stomach. So if it’s looking like you might get lucky tonight, don’t take it with dinner. Take it an hour before or a couple hours after.
CIALIS/TADALAFIL
Tadalafil was released into the wild as Cialis in 2003 by Lilly. It differentiated itself primarily by its long half-life of about 18 hours, meaning it can still be effective for up to 36 hours after being taken. So if your partner has a headache Friday night, you’re still in the game Saturday. It may take slightly longer to kick in, from 1-2 hours. Because it has such a long half-life, it can also be taken daily at a lower dose such that it remains at therapeutic levels in the bloodstream at all times. This means no planning! Everybody knows guys are bad planners. Additionally, it was later found that daily tadalafil is effective in reducing the severity of bothersome urinary symptoms such as frequency and urgency. This discovery resulted in countless patients telling me “doc, my erections are great but I am having some urinary issues. Let’s try that tadalafil stuff…”
SIDE NOTE – PDE-5 inhibitors are now used to treat pulmonary arterial hypertension as well, although used at higher doses.
There has been some evidence that they may also reduce risk of dementia. Lots to unpack there.