The ill-use of anti-depressants harm the users greatly because it increases dopamine release which causes increase of excitation. A highly poisonous chemical, cyanide for example, is also very dangerous to human beings. Therefore, considering the intensity of harmfulness and noxiousness a reliable, efficient and precise method is necessary for the detection of illicit drugs and toxic chemicals like liquids. Thus, a terahertz sensor for the detection of ketamine, amphetamine, cocaine, sodium cyanide and potassium cyanide are proposed on photonic crystal fiber (PCF) platform. Suspended hexagonal porous core in a topas substrate is used and extremely high relative sensitivity of 99.33% for ketamine is achieved. Moreover, other geometrical properties like effective mode area, birefringence, confinement loss and numerical aperture are also illustrated. The proposed sensor’s fabrication feasibility is also briefly discussed with respect to the recent technologies and this sensor can also be applied in guided terahertz transmission rather than bio-chemical sensing.