5-HT and 5-HT receptors are considered very similar, they share amino acid homology and their ligands expose similar binding properties thus they have similar pharmacophore. The pharmacophore model for these receptors ligands is qualitative and defines the relative positions of important groups. It is defined with following five main features: an aromatic group (usually the indole), protonated amine (a donor of hydrogen bond), acceptor of hydrogen bond, additional hydrogen bond site (both donor and acceptor) and hydrophobic region located between both hydrogen bond sites, see figure 2. The main binding points were concluded to be the protonated amine and the hydrogen bond site. It was observed that the double bond region in the indole was necessary for the agonism in this series of compounds. Figure 3 shows how different drugs fit the pharmacophore, with a C and N linked analogues of 5-HT agonist. The marked sites on the figure are responsible for the affinity. The pharmacophore can be characterized as amphipathic, that means that the structure has both hydrophobic and hydrophilic groups.