Why do doctors only prescribe drugs instead of natural remedies? For instance, turmeric instead of an anti inflammatory drug like Advil?
Natural remedies fall into two categories, those with relevant active ingredients (ie. those containing chemicals that will treat the condition) and those without.
Those without don't work, full stop. Walnuts won't cure migraine just because they look like little brains, old wives tale, there's no point prescribing something that doesn't work. I take it we can agree to this? Cool.
Now, the other group, this does contain active ingredients, willow bark contains acetylsalicylic acid (ASA) and can relieve pain, fever and inflamation, (pretty good huh?), plants in the digitalis family contain cardiac glycosides that can control otherwise potentially fatal heart conditions (even better!), this isn't woo woo or superstition this is real, wow! So why don't doctors prescribe the plants?
Three main reasons, firstly, and by far the least important, price, convenience and palatability. Would you rather swallow a tablet of synthesized ASA or gather willow bark, brew a foul tasting tea and force yourself to swallow it while, btw, being in pain? Would a manufacturer sooner spend years growing willow trees (that require a very particular environment) in order to harvest the bark then ship it out complete with wood fibre, or synthesize the ASA and ship tiny tablets of the bit that works? Which gives you pain relief at pennies a dose?
The second reason is that natural remedies are taking advantage of chemicals that plants create for themselves, not us, they make a lot of chemicals. Some are beneficial to us, some aren't. Some will kill you in surprisingly small doses. Plants can also absorb chemicals from their environment. Would you sooner take a tablet containing only the relevant chemical, or do you want a pot luck of chemicals including the one you want plus potential toxins?
Thirdly, dosage. The concentration of your active ingredient will vary from plant to plant, between different parts of the same plant, and over the course of time. Most chemicals that may save your life in the correct dose will kill you if you take too much. Take too little and it won't help and your underlying condition might kill you. Add to that preparation variations: was the water hot enough and did you let your herbal tea steep long enough or too long; did you macerate it enough, too little, too much? Did you have the right bit of the plant, a bit that's too strong, one too weak, one picked at the wrong time of the year, one that grew next to a waste disposal site? Or would you sooner have a pill with a defined quantity of the chemical that could save or kill you?
Choosing ‘natural remedies' over ‘drugs' is like throwing out your cooker and roasting your dinner over an open fire in the middle of your living room. Sure it can cook the food and it's traditional, but it's less convenient, will fill the room with smoke and may get out of control, burn your house down and kill you. We do things the modern way for pretty good reasons.
ETA: It's been noted in the comments that willow bark actually contains just salicylic acid not acetylsalicylic acid. It has some of the same effects, but the acetyl group makes it safer, which is why the acetyl group is added chemically to the natural occurring salicylic acid. Thanks tofor pointing this out (and adding another reason to prefer the pill!).