Michael Pollan: What Do Marijuana and Catnip Have in Common?

The following is an excerpt from The Pot Book edited by Julie Holland, M.D. (Park Street Press, 2010)

Julie Holland: Can we start with the catnip story?

Michael Pollan: I always kept a little patch of catnip in my garden for my old tomcat, Frank, who really liked it. It's not a very difficult plant to grow. The patch was hard to miss, because it was so shrubby. But every evening around five or six o'clock, just around the time that I was going to the garden to harvest something for dinner, Frank would come down there and look at me. What he wanted to know was where that catnip was, because he managed to forget every single night. And I would point it out to him or sometimes bring him over to it, and then he would pull some leaves off, sniff them, eat them, and start rolling in the grass. He was clearly having a powerful drug experience. Then he would sneak away and sleep it off somewhere.

But the interesting thing was, as much as this became part of his daily routine, he could not remember where the catnip was. And it occurred to me that this might be a kind of evolutionary strategy on the part of the plant: instead of killing the pest, it would just really confuse it. Killing pests can be counterproductive, because they breed or select for resistance very quickly. This happens with a lot of poisonous types of plants, as it does with pesticides. But if the plant merely confuses the pests or disables their memory, it can defend itself against them overindulging. Pure speculation, as I say in the book. It occurred to me that it might help explain what's happening with cannabis, which of course also disables memory.

Holland: So THC could potentially protect the plant from pests by discombobulating them so they forget where they found it?

Pollan: It potentially is doing that. The big question is why plants would evolve very specific chemical compounds that have this strange effect on the mental processes of mammals, and that's one theory that I came up with to explain it. There is also, of course, the pure-chance theory. Maybe the THC is doing something else entirely, like protecting the plant from UV rays or performing some other function for the plant, or maybe it does indeed kill insects. But it just so happens that THC also unlocks this particular receptor network in humans.

Holland: I am very interested in the idea that we co-evolved with cannabis on the Earth for ten thousand years and that we've got receptors for this plant substance inside our brains, that we've got cannabinoids and anandamide inside us. You've written about cannabis helping you forget as sort of a helpful strategy or adaptation, and there's a line in Botany of Desire about forgetting as a prerequisite to human happiness and mental health. I guess anandamide is our brain's own drug for coping and enduring. It's not just the benefits of forgetting -- what's that line, "Do you really want to remember every face you saw on the subway this morning?"

Pollan: Yes, Raphael Mechoulam keyed me in to that idea. We understand the evolutionary utility of memory, but we don't often think about the utility of forgetting. And it was that comment by him that made me realize that it's almost as important to be able to forget as it is to remember. Forgetting, in this case, isn't just a fading of the memory, but an active process for editing, because we take in far more information than it would be useful to retain. There's just so much detail in our visual field (not to mention the other senses) at any given moment that a lot of what our brains are doing is figuring out what is worth remembering, what can be shucked, and what should just be remembered for a little while and then let go. So we need some sort of mechanism for doing it, and Mechoulam's speculation was that one of the functions of anandamide would be to help us prune the sensory data of everyday life, short-term memory in particular. I found that a very persuasive theory, and it certainly gels with the experience of a brain on marijuana, because things that happened just minutes ago are gone, and I think that has a lot to do with the texture of the experience.