 Of the half-dozen Viagra-type drugs on the market now, Viagra itself may still have the greatest efficacy, but also the highest rate of overall side effects. It's still a pretty safe drug. Some guy swallowed 65 at a time and hopes he'd go out with a bang, but it didn't work. The most commonly observed acute side effects include headache, flushing, stomach upset, runny nose, and vision abnormalities. But that has been around for a decade. Some chronic effects may be cropping up. For example, glaucoma, one of the leading causes of blindness caused by degeneration of the optic nerve, up to nearly 10 times the odds of glaucoma among those using Viagra long-term. But it's cancer that has the medical community rethinking the safety of these kinds of drugs. Men with advanced prostate cancer often have to get a radical prostatectomy, a surgery that can leave them both incontinent and impotent, which can reduce their quality of life. Therefore a treatment concept called penile rehabilitation was introduced, where drugs like Viagra are given to counteract the side effects of the surgery. But there had been studies like this that found Viagra could decrease natural killer cell activity, and natural killer cells are a first line of immune defense against cancer. Now this was a study on women for something else, but it did raise concerns about giving Viagra to those battling prostate cancer. In terms of getting prostate cancer in the first place, men treated with Viagra-type drugs tended to have less of a chance of being diagnosed with prostate cancer. Yeah, but that may just be because they're ejaculating more. Higher ejaculation frequency may be associated with a lower risk of prostate cancer. It's interesting the reason they think why. Frequent ejaculations may decrease the concentration within the prostate gland itself of xenobiotic compounds, like hormone disrupting chemicals and carcinogens. Anything we eat can end up in our prostate. Drink a cup of coffee and you end up with caffeinated semen 10 hours later, smoke a cigarette, and the nicotine ends up in the same place. Or eat fish and end up with one seventh the healthy sperm count, perhaps because there's like three times the concentration of PCBs. But anyways, you don't know for sure about Viagra until you put it to the test. Nearly 5,000 prostate cancer survivors were followed, and those taking Viagra-type drugs did seem to have a little bump in their risk of the cancer coming back, but subsequent studies failed to find such an association. Move me to make this video is the unexpected connection between Viagra and melanoma skin cancer. If treated early, melanoma can be cured by cutting it out. But due to its proclivity to metastasize and about 20% of patients, it progresses to an aggressive invasive disease that can kill in a matter of months. And part of the way it does this is through a gene mutation in the cancer that induces melanoma cell invasion by downregulating an enzyme called phosphodiesterase 5. Does that word look familiar? That's what Viagra does. Viagra works because it's a phosphodiesterase 5 inhibitor. So Viagra may have the same effect in terms of promoting melanoma growth. You don't know, though, until you put it to the test. And Viagra use was associated with an 84% increased risk of subsequent melanoma diagnosis. And you put all the studies together and the association remains significant. So here we have this class of drugs found in medicine cabinets across the country. And the FDA does its best trying to ensure the safety and efficacy of such drugs, but you can't always anticipate the molecular consequences of inhibiting major cellular pathways. There is, however, an alternative explanation. Maybe users of Viagra are just naked more, thus giving their partners the opportunity to notice some suspicious mole or something, as only about 1 in 3 melanomas are discovered by the patients themselves.