Drugs.com states that penicillin sometimes makes birth control pills less effective, which may result in unexpected pregnancy. A backup method of birth control is recommended.
Penicillin is an antibiotic that is used to treat a wide variety of bacterial infections, according to Drugs.com. Before taking penicillin, patients are advised to inform their doctor if they have a history of medication allergies, asthma, kidney disease, a bleeding or blood clotting disorder, or diarrhea caused by taking antibiotics. Sometimes people with these conditions require special testing or dose changes in order to take penicillin safely. Women who are pregnant, plan on becoming pregnant, or are breastfeeding are encouraged to discuss this with their doctor prior to taking penicillin.
Drugs.com lists several side effects of penicillin, including nausea, vomiting, stomach pain, vaginal itching or discharge, headache, white patches inside the mouth or throat, and swollen or black tongue. Sometimes more serious side effects occur while taking penicillin, such as diarrhea that is watery or bloody, fever, chills, body aches, flu symptoms, easy bruising or bleeding, unusual weakness, urinating less than usual, severe skin rash, itching, agitation, confusion, unusual thoughts or behavior and seizures. The patient is advised to call the doctor promptly if these serious side effects occur.