Pills achieve this strengthening by stimulating the body to grow. As long as there is food to supply the body with energy, the stimulation will lead to growth until the body reaches its limit.
Tonics, on the other hand, cause the mind and spirit to grow. They increase the rate at which information is processed in the mind and increase the perception of the mind.
Both pills and tonics are produced from special plants and animals acquired in the wild. It is why they are effective.
They both have side effects, though. The side effect of using the pills is an increase in body temperature and constant itching.
The increase in body temperature is not only a matter of discomfort. The body can get so hot that the brain will be fried. So it is a matter of life and death.
This terrible fever is then accompanied by itching all over the body. The itching will be so bad that nothing he can do will alleviate it. The itching won't stop until the effect of the pill is over.