It could happen when two or more prescription or over-the-counter drugs don't agree with each other and wind up disagreeing with you. Doctors with the American Academy of Family Physicians suggest you follow a few easy steps to avoid any allergic reaction to any medication.
Read all labels carefully and make sure you understand all the side effects that can occur.
It could be easy to mistake an allergic reaction for a side effect. Follow the pharmacy labels; if they instruct you to take a glass of milk with your pill or instruct you to remain upright for the next half-an-hour, the pharmacists have a good reason why.
Make sure before your doctor prescribes any medication, they know all other substances you are currently taking, even daily multivitamins. Also let them know if you have any current allergic reactions to medication, such as penicillin. Don't take your multivitamins at the same time as your medication, and above all else, never operate any machinery when instructed not to do so.
You could put yourself and others in danger if you suffer an allergic reaction while behind the wheel.