How might acupuncture turn down pain? In 2010, scientists studied mice with pain from inflammation or a nerve injury.

They placed a thin needle near the knee and gently turned it. A natural chemical called adenosine increased in nearby tissue.

Think of adenosine as a message. It acts on a tiny receiver called the A1 receptor. This can help turn down pain signals, like a dimmer turns down a light.

The team compared two kinds of mice. One had these receivers. The other was bred without them.

After acupuncture, mice with the receivers were less sensitive to touch and heat. Mice without them did not show the same change. The A1 receptor was needed for this effect in these tests.

Caffeine adds a twist. It can block adenosine from using its receivers, including A1. Think of a seat that is already taken. The message cannot use that seat.

A later study tested caffeine in mice. In 2017, caffeine prevented the drop in touch sensitivity after acupuncture. After caffeine was removed, the effect returned.

Small studies in people gave mixed results. One found no link between daily caffeine use and the change after acupuncture. Another gave healthy people coffee or juice for four weeks. Coffee weakened some effects of acupuncture with electrical stimulation in pressure pain tests. Other results did not change.

So, this is not proof that coffee cancels acupuncture. These tests do not tell us whether avoiding coffee improves pain care, including cancer care. We still need studies in patients.