Most of the time, yes. The medicines that are ordered to be taken before meals need to be taken then to ensure the proper absorption of the medicine. It works on the stomach in a way that is only effective if taken prior to the meal, or to the extent that the medicine is not thoroughly effective if diluted by food contents.
Food can also adversely affect the action of the medicine.
Other medicines are designed to be taken on full stomachs, and some medicines can be taken either way. Sometimes when medication makes you nauseous, it may help to call the pharmacist to see if they will be less likely to do so if you eat first or maybe if you don't eat first. Medication is effective only to the extent that it is taken the way it was intended based on the drug manufacturer's specifications. Always read the little notes on the bottle for added instructions regarding the med. Alcohol and even some juices, like grapefruit juice, can affect the absorption and affect the medication may have on your system.