The mercaptopurine (MP) molecule's interaction with the pristine covalent triazine-based framework (CTF) was evaluated in the gas and the water medium. The S1 structure is the most stable form of MP/CTF complexes, with the Eads of −0.532 and −0.385 eV in the gas and water medium, respectively. The adsorption behaviour of the MP/CTF nanostructures is further discussed using band structure and partial density of state analyses. The MP drug adsorption reduced the band gap energy of the desired monolayer in the range of 47 to 71% for the studied complexes. The adsorbed drug on the surface of the CTF substrate can be released in the adjacency of tumour cells, and the therapeutic operation is carried out on the target cells. The recovery time indicates the suitability of the desired CTF as a carrier of the MP drug in drug delivery applications.