Some pharmaceuticals can initiate allergic reactions, as in the case of penicillins. In some people, administration of penicillin can induce production of specific antibodies and initiate an immune response. Activation of this response when unwarranted can cause severe health concerns and prevent proper immune system functioning. Immune responses to pharmaceutical exposure can be very common in accidental contamination events. Tamoxifen, a selective estrogen receptor modulator, has been shown to alter the humoral adaptive immune response in gilthead seabream. In this case, pharmaceuticals can produce adverse effects not only in humans, but also in organisms that are unintentionally exposed.