Cimetidine was initially developed as a drug to inhibit gastric acid production. It has few side effects and is well-tolerated.

Cimetidine can stimulate the immune system. It increases the number of certain white blood cells (CD8 cells), which are very important for the immune system. Cimetidine also increases the activity of natural killer cells, which are able to attack and kill cancer cells directly.

Some studies also discuss a direct effect on cancer cells. For example, cimetidine can prevent the growth of colon cancer cells and prevent metastasis.

A robust immune system is always necessary to fight cancer. Therefore, cimetidine can be used with any cancer.

In most cases, cimetidine can be safely used as an additive. Especially for immunocompromised patients, e.g., after previous chemotherapy, cimetidine is a good help.