Mild adverse effects include nausea, vomiting, diarrhea, headache, and dizziness ^L1893.

LD50 in rats is 535 mg/kg ^L1895.

Reported effects in humans in case of overdose include gastrointestinal disturbance, central nervous system effects, and superficial skin reactions. In one study, serum aspartate aminotransferase (AST) and serum alanine-aminotransferase (ALT) values were increased in approximately 2% of patients ^L1906.

Pyrantel should be used with caution in patients with severe malnutrition or anemia. Supportive therapy is recommended for anemic, dehydrated, or malnourished patients before administration of the drug ^L1898.

Pyrantel pamoate has been placed in pregnancy category C. This refers to the fact that animal studies have revealed adverse effects on the fetus (teratogenic/embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus ^L1894.Data on the use of pyrantel pamoate in pregnant women are quite limited. In mass treatment programs for which the World Health Organization (WHO) has observed that the benefits of treatment outweigh the risks, WHO allows the use of pyrantel pamoate in the 2nd and 3rd trimesters of pregnancy, due to the fact that the effects of pyrantel on birth outcome are uncertain. The risk of treatment in pregnant women already known to have an infection needs to be balanced with the risk of disease progression if treatment were to be omitted ^L1894. Individuals with liver disease are more susceptible to the toxicity in cases of pyrantel overexposure ^L1894, ^L1897.

There are no data regarding the presence of pyrantel in breast milk. Pyrantel is poorly absorbed from the GI tract; therefore, excretion into breast milk may be minimal. Some experts recommend that a single dose of pyrantel therapy may be given to breastfeeding women ^L1893.