A lot has changed in the areas of sexual health and STIs in the last several years that has led to some very positive shifts in how people have sex. For one, the use of HIV PrEP dramatically reduces someone’s risk of HIV. Also, effective HIV treatments mean that people with undetectable viral loads (the amount of HIV in the blood) cannot pass HIV on to others. This is more commonly known as Undetectable = Untransmittable, or U equals U. These two innovations have led to really significant improvements in HIV prevention, and have helped many have better sex lives. We have not, however, seen as much innovation in preventing other STIs such as chlamydia and syphilis. In fact, we have seen significant increases in both these STIs in many parts of the world over the last several years. This means that what we’re currently doing is just not enough to prevent these infections, and we need to “think outside the box” and come up with new tools to use against STIs. Using what we know about HIV PrEP, doxycycline’s other uses, and the results of the small studies on STI PrEP and PEP that have been done so far, we designed the DISCO study to test out this innovative idea on a large-scale.