Interesting point, valid concern. Most medicines have been derived from plants; which is one reason why protecting the rainforest is so important. Not trusting "natural" medicines that haven't been scientifically tested makes sense to the modern Western mind, but why not ask why "Science" hasn't tested these natural medicines? Why blame a plant or "natural" medicines that haven't been tested instead of blaming those who, for whatever reasons, haven't tested them? Many of these plants that have been labeled as being "dangerous" have been used by other cultures for thousands of years. Cannabis is a perfect example. For years it has been vilified and the victim of all sorts of crazy propaganda, yet only now (since the facade of the propaganda campaign has evaporated) is Science supposedly catching up, or more accurately accepting the facts. Cannabis oil has a long history of healing properties. Many scientists and scholars say it's mentioned in the Bible as kaneh-boson; holy healing oil.
I'm usually a fan of "Science," but when it comes to certain things I'm very skeptical. If science can put men on the moon, why can't they do adequate testing on plants that have been used medicinally for thousands of years? I can't help but think a major reason is because Science showing that many of these plants are indeed beneficial would cut into Big Pharmas profits which are dependent on people being prescribed often times expensive drugs that have been synthesized in a laboratory. Big Pharma wants us all dependent on their plant based synthetics instead of having access to the actual plants their products are synthesized from. They want prescriptions, not gardens.
I don't know anything about Mandrake. Obviously not everything that is natural is good for you. There are species of mushrooms that will kill you while others are edible. Throughout time people have discovered which natural occurring substances are beneficial and which ones are dangerous; usually through past use and common sense. I do know that many synthetic drugs are very dangerous and are responsible for killing many more than die from using plants. Even Tylenol can be dangerous to your liver, but you don't hear many people saying that because Tylenol can also kill you that it sums up their feelings on synthetic medicines approved by scientific studies.