Why do medications that eventually are linked to significant health problems pass the FDA and make it to market?
The answer is relatively straight forward. It all stems from the way that medications are tested and developed.
To get a drug approved, a company has to show a few things. First, and most importantly, that it is safe. This is done by first testing the drug in animals and seeing if anything unusual comes up or happens.
After this is done, testing is done in humans to see what doses are safe. The initial trials for safety are typically small and done over a short period of time. It’s really to see if there is any immediate reaction. This is Phase I testing.
Next, the trials are expanded to determine what doses are effective. This is Phase II testing.
Finally, with the knowledge that the drug is likely not unsafe, and what dose of it is likely to provide benefit for a condition, Phase III testing begins. These compare the drug to placebo and aim to test if the new drug is really that much better than taking no drug at all (or rather, taking placebo).
With all this done, assuming positive results from all three steps, the drug heads to the FDA and is hopefully approved.
The problem arises when a side effect is rare or abnormal or not tested for properly.
1) The testing is typically not done for more than a year. Some drugs are taken for years, so in many cases, the drug approval process will not catch side effects that take a long time to develop.
As horrible as it may sound, the way we approve drugs could lead to a drug reaching the market that causes a certain type of cancer in most people who take it in 50 years.
2) The testing is usually done in at most, a few thousand people. A side effect that occurs in 1/5,000 people who take it, could easily be ignored by testing
3) The testing can sometimes be done in a way that tends to accidentally ignore side effects.
For instance, the statistical methods used can obscure whether or not a side effect means anything (whether or not it was caused by the treatment).
Or the side effect could be not included as part of the side effects looked for and ignored.
Both of these tactics I have personally seen used.