Thanks for the query.
No, you should not take tablets without consulting the doctor.
As you are having 18 weeks pregnancy
, now the abortion
should be conducted as mini labor.
So you consult gynecologist, with her advice and under her supervision you have to go for the procedure.
Your previous pregnancies history also plays role here.
So use any tablets only after consulting the doctor.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429