Polypyrrole (PPy) fibre electrodes were studied to determine their ability to sense paracetamol (as a model drug) in the presence of the interferents dopamine and ascorbic acid. PPy was electropolymerised onto carbon fibres using cyclic voltammetry in the presence of two different counter anions: sodium dodecyl sulfate (SDS) and potassium nitrate (KNO3). The surface of the PPy.SDS and PPy.KNO3 fibre electrodes was characterised using Raman spectroscopy and scanning electron microscopy. The PPy.SDS-coated carbon fibre had a 14-fold larger electrochemical surface area compared to a bare carbon fibre (calculated using the Randles-Sevcik equation). The use of a large counter anion as dopant (dodecyl sulfate) produced fibres with a greater drug sensing response (cf. the use of smaller nitrate anion). The use of the PPy.SDS fibre electrode in differential pulse voltammetry (DPV) allowed sensing of paracetamol with a detection limit (3σ S/N) of 34 µM. For the anodic peak current (0.5 V vs. Ag/AgCl), a linear response range was observed for 50–500 µM. At a paracetamol concentration of 100 µM, the DPV anodic peak current (at 0.5 V vs. Ag/AgCl) was unaffected by the addition of interferents: 100 µM dopamine and 100 µM ascorbic acid. A real-world application of drug sensing was trialled with the anti-psychotic medication clozapine; where the PPy.SDS carbon fibre could sense clozapine with a detection limit of (3σ S/N) of 6 µM and a sensitivity of 15 μA cm−2 μmol−1 L.