It's a question as old as boner pills: what happens if I take too many boner pills? Well, a few unfortunate people have learned the hard way.

Sildenafil, the drug commonly referred to by the brand name Viagra, is used to treat erectile dysfunction as well as pulmonary hypertension. Extensive trials and follow-up studies have deemed it a safe and effective treatment for erectile dysfunction, for which it is most commonly used. 

Like most drugs, there are common side effects such as headaches, nausea and dizziness, blocked nose, and hot flushes. In rarer cases, especially when patients have exceeded the recommended dose, some patients have gone through much worse.

One report says that a Colombian man in his 60s ended up having his penis amputated, after he intentionally took too much of the drug in order to impress his girlfriend in the bedroom. After several days of having an erection, he sought out the local hospital for the pain, where the doctors found his penis to be fractured and gangrenous. His penis was amputated to swap the gangrene from spreading, according to the Independent.

Another, less extreme, complication can be problems with vision. One 31-year-old ordered liquid sildenafil citrate off the Internet. Rather than take the recommended dose using the provided pipette, he later told doctors, he had drunk the medication directly from the bottle like he was enjoying a Sprite. The man estimated that he had taken far more than the recommended dose. 

"A short while after ingesting the substance, the patient began to notice a red tint to his vision along with multi-color photopsias [flashes or floaters in the vision] and a sense of decreased contrast," his doctors wrote in a case report. "The following day, the photopsias resolved, but the decreased contrast and red-tinted vision remained."

Typically, visual symptoms like this resolve within 24 hours, the team explains. In this case, however, they were still present three months after admission, despite several attempts at treatment, and finally resolved after a year.

"The changes seen in our patient are consistent with photoreceptor toxicity, especially in the macula," the team said in their case study.

"Sildenafil citrate can also inhibit 6-phosphodiesterase (PDE-6) in retina. PDE-6 is an important substance to convert optical signals into electrical signals in the process of vision," another team explained in a case report, after one of their patients experienced visual disturbances after taking the drug long-term. "Inhibition of PDE-6 can lead to visual abnormalities and color vision defects."

Other less common side effects include fainting, chest pain, heart attacks and stroke, as well as an erection that lasts more than four hours.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.