Will smoking marijuana and doxycycline have negative effects on my body if taken together?

Probably not: Since marijuana is, for whatever reason, illegal, it is impossible to study the interactions as it is with alcohol. This is unfortunate, but i very much doubt there's any danger here. I feel life offers too much else for me to be passive and self-absorbed, and i try to obey even the laws i may disagree with. But it's your choice. Peace and love.