system
Given the following post, respond as if you're commenting on Reddit:
human
A lot of drugs are derived from plants. Why not just eat the plants? 

I keep hearing about new wonder drugs derived from plants - many of which seem to have long-known (according to local tradition) curative properties. If that's the case, then why not just use the whole plant? Is there a good reason, apart from making Pfizer and GlaxoSmithKline a lot of money, that the source material just doesn't cut it? If its just a concentration thing, couldn't you just eat lots of it to get the same effect?
gpt
There are a few reasons for this. By the way, microorganisms also produce a lot of drug compounds. 
Firstly, the concentrations of active compounds are often low, and nobody wants to eat vast quantities of plant material to get an active dose. 

Secondly, the concentrations of active compounds often varies greatly between different batches, so there's no way of knowing how much you're getting. 

Thirdly, the plants may contain other compounds which are poisonous or have unwanted effects.

Finally, compounds taken from nature are usually not ideal drugs - they are usually chemically modified to optimise their beneficial effects and minimise side effects.