A north central state police of Guanajuato said the attack took place in the city of Irapuato. Three of the seven injured are in serious condition.
The attackers apparently targeted everyone in the rehab center. State police said no one was kidnapped.
Guanajuato is the scene of a bloody battle between the cartel of Jalisco is gangue local, and the state has become the most violent in Mexico.
No reason was given for the attack, but Governor Diego Sinhue said that gangs traffickers appear to be involved.