Bioenhancers are such agents, which by themselves are not therapeutic entities but when combined with an active drug lead to the potentiation of the pharmacologic effect of the drug. Many synthetic and herbal drugs suffer from the problem of low bioavailability; low membrane permeability is the major cause, lower lipophilicity, ionic characteristics, poor water solubility or P-glycoprotein. This paper highlights the various bioenhancers and their mechanism that enhance bioavailability when use combinely with API. The herbal bioenhancers are easily available, safe, free from side effects, minimizes drug toxicity, shortens the duration of treatment, and lowers the drug resistance problems and minimizes the cost of treatment. Herbal bioenhancer are use for various categories of drug like neutraceuticals, antibiotics, antitubercular and anticancer and cardiovascular for immediate effects. Bioenhancers are recently used in many novel drug delivery formulations such as liposomes, transferosomes, ethosomes etc. Researchers must be solve these issues of drug toxicity to deliver a safe and effective dose of drugs to attain desired pharmacological response.