Orlistat is an anti-obesity drug. But it has many side effects drowsiness, flatulence, diarrhea etc. Your hypothyroidism must be controlled as it causes weight gain. But drugs like orlistat don't give magic results. They aid in weight loss and may help you lose 5 to 10% of your body weight. Please consult a physician who will educate you regarding all these aspects. PS: there are many dangerous anti obesity drugs (amphetamine like drugs) available in the back market. Please do not use any of these as they could cause fatalities which is why they are banned.
No you cannot take any tablets without consulting any doctor. It is dangerous for your health and you will be solely responsible. Consult a doctor and get you evaluvated. Uncontrolled hypothyroidism can itself make you gain weight