No side effects from Silicea Gel have been reported yet. There is no data that Silicea could be toxic for the kidneys. Allergic reactions are totally unpredictable side effects. Allergic reactions can occur to any kind of medicine. Allergic reactions can manifest differently, from the easiest skin rush to the heaviest anaphylactic shock. If you get any sign of allergy (skin rash, itching, hard breathing, hypotensionâ¦) stop taking the medicine and consult your GP immediately.