Is it permissible for a person to invest a sum of money in the pharmaceutical trade in exchange for a fixed profit of 20% annually from the capital, based on the understanding that the money is for investment and not lending, and that the pharmaceutical trade does not carry a percentage of loss?

A valid Mudarabah (profit-sharing) contract must specify a known proportion of the profit, such as a half or a third. It is not permissible for it to specify a known amount of the principal capital, for stipulating a specific amount from the principal capital invalidates the Mudarabah, by scholarly consensus.