There is no scientific evidence that ingesting niacin can help an individual pass a urine drug test as of 2015, according to the Centers for Disease Control and Prevention. Although claims on the Internet imply that taking niacin is an effective way to mask the presence of tetrahydracannabinol, or THC, the main psychoactive ingredient in marijuana, this is not substantiated scientifically, and the CDC advises physicians to become familiar with the adverse drug reactions that result from the misinformation.
Niacin can cause serious side effects that require immediate medical attention, including severe stomach pain, vomiting, jaundice, dark urine and loss of appetite, reports Drugs.com. Because the liver metabolizes niacin, individuals with liver disease should not use niacin, nor should those with stomach ulcers or bleeding disorders. Niacin can pass into breast milk and injure infants; nursing mothers and pregnant women should avoid the vitamin. Common side effects include dizziness, tingling and flushing skin, sweating, nausea, and muscle cramps and pain. These symptoms usually resolve over time as the body adjusts to niacin, but they can worsen if niacin is combined with hot beverages or alcohol.
Niacin, or vitamin B3, is found naturally in plants and animals and often treats high cholesterol, high triglycerides and coronary artery disease, explains Drugs.com. Individuals who have experienced a heart attack often use niacin to lower their risk of another attack.