A concoction has been invented that can influence a target to fall in love with an individual. This works in two parts. The user must drink one type of potion to emit certain hormones while the unsuspecting target drinks the other version of the potion. The hormones trigger the emotions of the target, encouraging strong feelings of arousal and love in them. These substances are odorless and don't build up in the body. It evaporates from the bloodstream rather quickly, and doesn't leave traces of itself in blood, urine, or fingernails like other poisons. The affect on a target is not permanent and must be consumed at certain intervals or the affect will wear off.
This potion has the potential of being abused, and many have been taken advantaged of in society, and it has been made illegal as a result. However, there are others who have used it as an excuse to get out of responsibilities or bad decisions. There is difficulty in proving veracity of these claims because the substance is so hard to detect.
How can one detect that this potion has been used in an individual?