The brain is a champion of self isolation. In other parts of your body, drugs and nutrients enter through the lining of blood vessels. While the brain is full of blood vessels, specialized vessel walls tightly regulate what can get in. This “blood-brain barrier” is important for protecting the specialized environment of the brain, but it is also a problem when trying to treat conditions like brain cancer or neurodegeneration as drugs can't get in. 

We do know of some drugs that are really good at getting through this barrier, either by slipping in or by breaking the barrier down. A new study, currently published as a pre-print, has found that giving rats a drug that easily crosses the blood-brain barrier helps other drugs get into the brain, even if they aren’t normally able to. 

What is this barrier breaking drug? Methamphetamine, also known as meth. Meth’s powerful effects are partly due to its ability to get into your brain. At low doses, it can increase a process called fluid phase transcytosis, in which a drug is packaged and transported into the brain by the cells lining blood vessels. While previous studies have shown this is how low dose meth enters the brain, this new study is the first time it’s been shown that it can bring other drugs along for the ride.

Researchers gave low doses of meth to rats, along with therapeutic drugs that don't easily cross the blood brain barrier. They then looked at the rats' brains to see what molecules were present. The therapeutic drugs got into the brain far more easily if meth was given at the same time. In another experiment, meth was able to help a chemotherapy drug enter the brain, which increased survival in a mouse model of brain cancer. 

Meth isn’t often associated with medicine, but it is FDA approved for some uses. In cases such as aggressive brain tumors, it may be worth using a little meth for a lot of chemotherapeutic.