Taking antihistamines can help fight off an allergic attack. But there is new research suggesting that it also might make the next attack even stronger.

Researchers studied 50 mice that were injected with bee venom, a substance that causes nearly all organisms to develop an allergy upon exposure. Half of the mice were also given doses of the antihistamine Clemastine.

Six weeks later, the mice were injected with more bee venom. The mice that had been given antihistamines reacted more violently to the second venom injection. The researchers theorized that the mice given allergy medication had no chance to build up a tolerance to the allergen.