The saying "you are what you eat" applies to bees too. The type of nectar they consume to create honey has a lasting chemical effect on the resulting sweet stuff. And, if the bees employ nectar from the toxic Rhododendron flower, guess what? You get toxic "Mad Honey".
In areas that have Rhododendrons growing wild -- Turkey, the Middle East and the Mediterranean, for example -- this effect has been well-known for millennia. In fact, the practice of dropping tainted honeycombs in the path of invading armies has been a well-known and often-used military tactic as far back as the Romans.
Mad honey is packed with gryanotoxin, a chemical compound that binds to the sodium channels on a cell's membrane. This prevents the channels from closing -- it's essentially the same process as Viagra, keeping blood flowing to a person's -- ahem -- "extremities". Effects can take from a few minutes to three hours to set in -- including, according to Wikipedia, "excessive salivation, perspiration, vomiting, dizziness, weakness, paresthesia (numbness) around the mouth and low blood pressure." However if one overdoses on mad honey the symptoms may increase to a loss of coordination, severe muscular weakness and bradycardia -- when the heart's pace is too fast or slow.
Mad honey is still used as a traditional marital aide in the Middle East. A couple just recently was admitted to a local Turkish hospital complaining of chest pain. Upon examination, doctors found they also had symptoms of confusion, low blood pressure, a slowed pulse and had both suffered mild heart attacks. The couple later admitted that they had regularly been consuming the mad honey over the course of a week -- up to a tablespoon at a time -- in order to add an extra bit of zing to their lovemaking. A heart attack, from a mere tablespoon of the stuff! They both did eventually recover but will likely just have to get their freak on in the old-fashioned way. [Neuroskeptic - Boing Boing - Grayanotoxin Wiki]