I think the amount you need is calculated on body weight and length of procedure. Some of us do need a larger dosage to put us under (I am one of them) and just by chance happen to be a redhead. That is not a medical fact.

Yes, because it is believe that the genes that cause the red hair makes them more sensitive to pain. And because they are really thick headed and means you need more to knock them out.

This link between hair color, pain, and anesthesia may be traced to a glitch hidden deep within redheads' genetic codes, suspects researcher Edwin B. Liem, MD, an anesthesiologist at the university. Receptors for melanocyte-stimulating hormone, the hormone that tells cells to produce the skin--and hair--color pigment melanin, don't function normally in redheads. As a result, most redheads end up getting sunburned instead of tanned. The dysfunction might indirectly stimulate a brain receptor that boosts pain sensitivity, Dr. Liem says. "In a nutshell, we think redheads are likely to experience more pain from a given stimulus and therefore require more anesthesia." Anesthesiologists have long noticed that surgery patients with fiery manes seem to need more anesthesia. To test the link, Dr. Liem and other researchers had 10 redheads and 10 brunettes inhale desflurane, a common general anesthetic used before surgery. They gave the volunteers (all women) mild electric shocks and adjusted the desflurane dose until they felt no pain. Redheads needed roughly 20 percent higher doses. (Presented at the American Society of Anesthesiologists annual meeting, 2002) Redheads may also need more injected anesthesia and higher doses of other pain relievers, Dr. Liem says. But this remains to be studied. "From a scientific standpoint, this is the first genetic marker that affects anesthetic requirements," he says. "It might be worth mentioning this to your physician if you are a redhead." http://tinyurl.com/25vyrs

I've been doing a lot of reading on the subject and I find it interesting that research deduces that redheads seem to be simultaneously more sensitive to and capable of enduring pain. (might be why so many are dominatrices)

A 2002 study conducted by researchers at the University of Louisville in Kentucky, proved what anesthesiologists -- doctors who oversee the administration of anesthesia -- have believed for some time, that redheads are more difficult to knock out. http://health.howstuffworks.com/redhead-anesthesia.htm

Yes. ". Need more anesthesia during surgery. Redheads need 20 percent more anesthesia than their dark-headed counterparts. Because the MC1R gene belongs to the same family of genes that play a role in pain, the mutation causes redheads to be more sensitive to it. Aug 18, 2015" http://www.medicaldaily.com/8-ways-having-red-hair-affects-persons-health-pain-sex-348198

Hmm! I just turn them on!

not that i know of