**3.5 Toxicological effects**

Toxicity referred as the production of toxic effect that is due to the entry of the xenobiotic components which are external chemical substances for humans/animals that alter the function of the administered drug. Instead, there is a theory in the name of 'Darwinian toxicology' that shows the contrast view on toxicological effects by stating that these effects are the body's protective response against the drug has been administered to the body [14].

The detection of toxicological effects remains as a complex issue. It is even yet difficult to solve the toxic effects of drugs which are being subjected to the clinical trials. Perhaps, the drug passes all the pre and post drug designing/discovery stages by exhibiting positive results till the end of the clinical trials, it may become a huge problematic situation if it shows toxic effects after marketing the drug. It is inevitable to repeat the process again from the start point. This shows the importance of understanding the behavior of the drug molecule at the molecular level to avoid such toxicological effects. One of the "omics" concepts, biomarker identification helps to screen drugs with its associated toxic effect.

There are five different toxicity conditions, the first one being "On-target" that is the mechanism-based toxicity caused due to the interaction of drug with the same target to produce required pharmacological response. The second one is "Hypersensitivity" and "Immune response". The third one is "Off-target" toxicity, in which the drug interacts with alternate target and causes toxicity. The fourth one is "Bioactivation", which converts multiple drugs as product of metabolites (reactive). These elements manipulate and being a starting point of toxicity of the proteins that has to be avoided. The fifth condition is an unfamiliar condition named as "Idiosyncratic reactions" known as troublesome responses [15].
