Centuries ago, women figured out what to feed people in order to heal them, build their sex drive, sedate them, and even poison them. And since it was a long time ago, these things were considered "spells" and had the idea of witchcraft tagged onto them. "Cauldrons", simple cooking pots, really.. were the main "brew" bowl of choice since everything was cooked over a fire. And all these women were doing were using old school chemistry, plants and food to control the body.
Our bodies are just a big sack of chemicals that respond ridiculously well to other chemicals. That's how chemistry works! Chemicals love or hate each other, and act like people. Everything in the universe behaves in the same way, and that's due to the the laws of physics and chemistry. And so, it is incredibly easy to manipulate behavior if you know how to do it. But it's an art as well as a science, and practice makes perfect. You also must consider mutations to food and bodies that have been made in response to changes we've made in our food industry.
In order to start, you must first know what it is you want to change in the body. Looks? Hormonal imbalances? Sickness? Fatigue? Weight? Most things are possible. The only thing that would be almost impossible is something like changing your hair color, and you can do that with a box from the drug store. I'll choose "depression". It's a common problem.
Secondly, start researching the chemicals and hormones responsible for this problem. Usually, psychologists and other health professionals concentrate more on serotonin production. Most depression and bi-polar symptoms come from a lack of it, then misfiring of the neurons when they're not passing it along properly. The drugs administered for depression such as Zoloft or Prozac, for example, work by inhibiting the re-uptake of serotonin. You see, when your body produces serotonin, it passes from one neurotransmitter to another. And after it passes, whatever isn't used is sent back to the first neurotransmitter. If someone isn't producing enough, these drugs will keep the first neurotransmitter from sucking it back up. More will be eventually deposited into the bloodstream. But if someone isn't producing enough to begin with, there's still not going to be much of it regardless of the help of any drug. That's not a perfect explanation, but it's the best I can give while trying to remain simple and not go into anything too complex or confusing.
So the best way to help out serotonin production is to stimulate it. Not to only try to save the tiny little bit you have. First, you have to get sunlight, exercise, massage helps, and brain power: you must recall good memories and things that made you feel good. These four things will help wake it up and stimulate production. In addition, you can use food to build it up and make it stronger: Nuts, brightly colored fruit, and protein. And stay away from anything containing a lot of carbohydrates. They'll totally shoot it back down again.
Our bodies work like machines. There are organs and hormone systems that work as thermostats and measurement devices, making a decision as to which chemicals to release and which ones you don't have enough of. When you give it the right fuel, it will do amazing things. There is plenty of information that is available to anyone who will take the time to read it. It's easier than you think to control the body through chemicals. Our feelings, emotions, decisions, most physical abilities.. they all thrive off chemicals. Don't be afraid to make them work for you.