PIP: Users of natural family planning (NFP) methods of birth control should be aware of the medications that can effect their ability to read their fertility signs. Antihistamines and decongestants are the most common medications that can affect the mucus signs. Antihistamines tend to dry up the mucus while decongestants tend to liquify mucus. Some anti-depressants sometime act like antihistamines while steroids like cortisone do not change the signs but can lengthen the cycle. Although with cortisone it seems to depend on when in the cycle it is administered. Finally, while antibiotics do not effect the cycle they can cause a secondary yeast infection. These yeast infections can in turn make reading difficult. The solution is to eat yogurt, take lactobacillus tablets or drink acidophilus milk before, during and after taking antibiotics.