G Protein Coupled Receptors (GPCRs) can form dimeric or higher ordered oligomeric complexes, which can remarkably influence the signalling of these receptors. Bioluminsecent Resonance Energy Transfer (BRET) titration experiments are the gold standards to prove the physical interaction between the protomers of a presumed dimer. In this method the energy transfer (BRET signal) is measured between a luminescent (energy donor) and a fluorescent (energy acceptor) labelled receptor. BRET signal can increase not only due to a specific interaction (dimerization) but due to the random, non-specific interactions between donor and acceptor. To distinguish between the specific and non-specific interaction, BRET signal is measured using fixed amount of donor and varying amount of acceptor labelled receptors, and BRET signal values are plotted as a function of acceptor/donor ratio. In the case of specific interaction this plot shows a saturation curve, while in the case of non-specific interactions it shows a lineal relationship. Maintaining constant amount of donor labelled receptors is strictly required to the correct interpretation of BRET titration experiments, but it is very hard to achieve in a transient transfection system. In our work, we analysed the effects of changing donor levels on BRET titration curves, and set up a system, where it is possible to distinguish between specific and non-specific interaction even in the case of changing donor amount. To analyse the effects of changing donor levels on BRET titration curves, we performed Monte Carlo simulations. The results showed, that in the case of non-specific interaction, the BRET signal is only dependent on the amount of acceptor, while in the case of specific interaction it depends on the acceptor/donor ratio. Our simulations also showed, that in the case of changing donor levels, even non-specific interaction can lead to saturation BRET titration curves, which can lead to false interpretation of experimental results. We tested our simulation results in an inducible dimerization system, where the non-specific interaction between FKBP labelled donor and FRB labelled acceptor molecules could artificial changed with the addition of rapamycin into a specific interaction. Our experimental results verified our simulations. With these new analysis methods, we examined the dimerization between various GPCRs (type I and II angiotensin receptor, V2 vasopressin receptor, β2 adrenergic receptor, calcium sensing receptor, CB1 cannabinoid receptor).