Epigenetic enzymes HDACs enzymatically remove acetyl groups from ε-N-acetylated lysine residues in many protein substrates, including histones and non-histones. Different histone deacetylases (HDACs) have different biological functions and are recruited to certain genomic regions. HDACs are clinically authorized cancer treatments with major biological roles. These chemicals are also being studied for treating Alzheimer's disease (AD), metabolic disorders, viral infections, and multiple sclerosis. Around thirty HDAC inhibitors are being researched in clinical trials, in addition to the five authorized drugs. This review discusses HDAC inhibitor drug discovery progress. It analyzes the logical design of these inhibitors based on structure, isoform selectivity, pharmacology, and toxicity. The goal is to update medicinal chemistry researchers and speed medication discovery. Cancer is multidimensional, thus targeting two components with a single drug is an effective and beneficial method. Given its role in cell proliferation, metastasis, and death, histone deacetylase (HDAC) has been intensively researched as a prospective cancer treatment target. Clinically licensed HDAC inhibitors include vorinostat and panobinostat. Low efficacy, lack of selectivity, drug resistance, and toxicity limit their efficacy. HDACs that can target two entities are therefore popular. Combining a histone deacetylase (HDAC) inhibitor with other anticancer drugs has been shown to improve non-selectivity and drug resistance in single-target therapies.