I don't have ED but I was curious if my erections could be stronger. I spoke with my doctor and tried Cialis and Viagra. Since they have much different half-lives, I thought I'd try the following: Taking 10-20 mg Cialis every 2-3 days, then taking 20-40 mg Viagra (generic sildenafil) before sexual activity. My questions isn't whether this is effective - it certainly is. But is there any risk to doing this? I moved so I don't have a doctor right now.