This page is just a stub at this point and is far from a comprehensive report on possible risks and nuances of helminth (specifically hookworm) therapy. Helminth therapy is not approved by any national health organization at this writing, although preliminary studies are ongoing. People undertaking this therapy must understand that they are undertaking the responsibility of researching the risks.
Contraindications (people who should not try hookworm therapy)
Female patients who are, or who may become pregnant
There are several reports in medical literature(1) of hookworms getting into a fetus. This is definitely not safe therapy, in the infective stage, for pregnant women.

Patients with anemia, since some helminth therapy (hookworm) has the potential to slightly lower hemoglobin levels, understanding and correcting underlying anemia would should precede any treatment with helminths.
  • Patients infected Campylobacter jejuni, which may result in serious infection, including septicaemia.1,2
  • Coinfection of Schistosoma mansoni (Schistosomiasis) with Toxoplasma gondii(toxoplasmosis) is associated with severe liver pathology and death in mice. Coninfection with other helminths has not been studied, but ruling out the presence of toxoplasmosis seems like a prudent idea, before undertaking helminth therapy. 1,3
  • Patients with conditions for which there is no known evidence that this therapy will work. This would include cancer, heart disease, HIV infection and many others. Why increase risk with no clear evidence of success?

From http://wormtherapy.com/faq.html#faq3.

Is it safe?
This is a more difficult question to answer than it may appear.
It is widely accepted that more than a billion people harbor active hookworm infections on the planet. As many as 8 million have tapeworm infections. It is also presumed that a majority of them are asymptomatic.
It is argued by some that this means safety is well established for these organisms at the dosage used for therapy. We strongly disagree with this idea. The re-introduction of worms into an already dysfunctional immune system is fraught with dangers known and unknown. While we can take steps to mitigate the risks that are known there is little we can do for those risks unknown. It is of the utmost importance that you read the known risks and take additional time to factor in the unknown risks before you make a decision to try an experimental therapy.Read more at opensourcehelminththerapy.org