The intestine is one of the most important sites for the metabolism of several xenobiotic compounds. In addition to intestinal drug-metabolizing enzymes and drug transporters, gut microbial enzymes modulate the biotransformation of orally administered drugs in the gastrointestinal tract. Antihypertensive drugs such as amlodipine and nifedipine could be metabolized by gut microbial enzymes, which may influence drug absorption, leading to changes in pharmacological potency of the drug and eventual failure of the appropriate blood pressure control or unexpected side effects. This may suggest that there are additional mechanisms that can alter the therapeutic efficacy of antihypertensive drugs, especially in certain pathological conditions of the gastrointestinal tract or with concomitant use of substances such as antibiotics and probiotics that might alter the gut microbial composition. This review describes the metabolism of antihypertensive drugs by hepatic and intestinal microbial enzymes in an attempt to understand the potential effects of gut microbiota on their pharmacokinetics.