The proper level of HIV meds in your blood makes the difference between the success or failure of a combo, and it lowers your odds of experiencing worse than normal side effects from a drug. But measuring drug levels (therapeutic drug monitoring/TDM) is controversial, expensive and hard to get. Many people living with HIV/AIDS would welcome research for and access to TDM to help them individualize their HIV treatment. Now, a new method for evaluating med levels in your blood may be on the way: testing hair samples.

A team at the University of California in San Francisco found that hair samples gave reliable readings of levels of one HIV med class, protease inhibitors (PIs), correlating closely with treatment success. If the testing proves reliable in further studies, you won’t have to go all cue ball to test, either—10 to 20 strands will do.