According to arstechnica.com, scientists have discovered that a synthetic genetic circuitry can be triggered with caffeine. For a real world example, the researchers worked with a group of mice. When the mice sipped coffee, cells implanted in their abdomens tuned on. This led to an increase in a hormone that increased insulin production and decreased blood sugar levels, effectively treating type 2 diabetes. The active element is the caffeine in the coffee, so tea would also work to trigger the response.