Is it permissible to work for a pharmaceutical company that produces medical compounds and requests blood samples from volunteers in exchange for money to ensure the drug dissolves in the body, knowing that most of these compounds are safe and have no side effects?

What the company does in studying a medicine on a person or persons by taking blood samples in exchange for a sum of money is a permissible form of ijarah (leasing/hiring), provided the conditions of ijarah are met. These conditions are: that the ijarah applies to the usufruct (benefit) and not to the consumption of the object itself; that the usufruct is permissible; that there is an actual and lawful ability to obtain it; and that the usufruct, the wage, and the duration are known. If these conditions are met, then there is no harm in it.