Every time Westerners study people living in the natural world as hunter gatherers, or peoples living from shifting agriculture in remote forested areas, they find that people have a hugely detailed knowledge of the medicinal and tonic properties of the wild plants and animals around them. Even chimpanzees have been observed seeking out the leaves of certain plants when they are obviously 'off color'.
Plants contain powerful and sometimes dangerous chemicals.
There is a well known saying which sums up the dangers - 'there is a thin line between pharmacology and toxicology'. In other words, while the correct dose may help you, too high a dose may make you very sick indeed. Tonics are not medicines. They act in a general way, possibly mimicking or stimulating the production of certain hormones. The best 'tonic' is excellent natural food, excellent sleep, freedom from worry, and regular exercise.