In most instances, when someone sues a pharmaceutical company because they were injured while taking a drug, they’re filing a failure-to-warn lawsuit. What a failure-to-warn lawsuit does is allege that a company knew its drug had certain risks, but didn’t disclose them.
For example, there are many lawsuits filed against the makers of Reglan, a drug often prescribed to individuals with heartburn. Long-term Reglan use (more than 12 weeks) can cause serious movement disorders. For many years, the Reglan label didn’t accurately explain how high the risks of developing a movement disorder really are. So people who took Reglan and got a movement disorder file a failure-to-warn lawsuit.
This is grossly simplified, but to win a failure-to-warn lawsuit, you have to prove that (a) The manufacturer knew their drug had a risk of causing a certain injury; (b) the manufacturer didn’t accurately convey that risk; (c) that you suffered that injury; and (d) that you wouldn’t have taken the drug had you known of the risk.