All healthy people are alike, but all sick people are sick in their own way. You can not find equally sick people. Treated by different combinations of drugs two similar patients, i.e. patients with similar sicknesses, are moving on diverging roads. This is due to the fact that the drugs they take interact not only with them, but also with each other. If you take a lot of different medications, you might get cured of something, but you will definitely get something else.
How many drugs are there? There are different answers available on the net, averaging around 12000. Sounds reasonable, as there are about 12000 diseases in ICD-9 (International Classification of Diseases of the World Health Organization)*. Combinatorics teaches us that the number of possible interactions between 12,000 drugs is 2^12000 (a number with 3613 digits, which is greater than the number of atoms in the visible universe). If you believe that there exists some supernatural being that is able to study all these drug interactions and find all of them health-improving, then you definitely need medication.
Now we know why every sick person is sick in their own way (they use different combinations of drugs to reach unique complaints). But why are the healthy people alike? Because they do not take any medications.
* this is a translation of an old text of mine, now we have ICD-11