Phenobarbital 375years. Phenobarbital is known to alter adrenal and thyroid mechanisms. Per-
sons suffering from a body chemistry disorder called porphyria are supposed
to avoid the drug. Skin rashes and sores have been attributed to phenobarbital.
Scientists suspect the drug causes liver damage in dogs, but an experiment
testing a group of dogs for over six months was unable to confirm that sus-
picion.
Abuse factors.Characteristics are the same as for barbiturate class depres-
sants in general.
Drug interactions.Birth control pills might not work properly while a
woman is taking phenobarbital. The drug may interfere with medicines de-
signed to reduce blood clotting. Phenobarbital lowers blood levels of an an-
tischizophrenia medicine called clozapine and thereby affects proper dosage.
Persons taking phenobarbital in a task performance test typed more slowly
but more accurately, catching and fixing more errors than when a placebo was
used. Taking alcohol at the same time increased both speed and errors, but
typists believed they were working as well as ever and were unaware of their
worsening inaccuracy. From results in variations of the experiment the re-
searchers concluded that alcohol boosts some effects of phenobarbital.
Cancer.In some mice experiments the drug promotes liver tumors, but com-
plexities in the results have deterred researchers from making conclusions
about the drug’s ability to do the same in humans. Scientists do find that
persons using the drug have higher rates of liver and lung cancer, but a cause-
effect relationship has not been demonstrated. In contrast, cigarette smokers
who use the drug have lower bladder cancer rates than nonsmokers; as a
partial explanation, researchers suspect the drug may reduce the amount of
chemicals in tobacco smoke that cause bladder cancer.
Pregnancy.In animal experiments birth defects caused by phenobarbital are
described as “profound and prominent.” For example, pregnant mice dosed
with phenobarbital produce offspring with retarded muscle development, and
pregnant rats receiving the drug produce offspring with heart defects.
Debate exists about whether phenobarbital causes human birth defects.
Medical records in 151 human pregnancies from the 1970s into the 1990s gave
no indication that phenobarbital alone causes malformations, a conclusion
supported by another study of 178 pregnancies. In Europe phenobarbital has
been classified as safe for using during pregnancy.
Yet a review of almost 20,000 pregnancies found that 4.6% of children born
to women who used phenobarbital during early pregnancy had birth defects,
almost twice the rate suffered by children from women who used no drugs.
An international examination of almost 1,000 birth outcomes in Asia and Eu-
rope put the rate of all defects (serious or not) associated with phenobarbital
at 5%. Investigations have associated phenobarbital with heart defects, facial
deformities, urinary tract malformations, and incomplete development of fin-
gers or toes. One study found that about 20% of pregnant epileptic women
taking the drug gave birth to children with serious birth defects, a finding
consistent with still more studies. One study compared pregnant epileptic
women who used phenobarbital with those who did not and revealed that
women using the drug had infants with smaller head size. As children from