Email Experts say you could start to feel extremely drowsy within 30 to 45 minutes if you are not careful. As with any prescription medication, you need to be careful about sticking to recommended dosages of codeine (either as prescription pain-relief tablets or cough syrup). Codeine is an opiate, so it’s possible to become drowsy or disoriented without intending to. But how much codeine does it take to make you intoxicated? When it Comes to Codeine, How Much Is Too Much? The amount of codeine needed to get you high varies depending on how much you take, body weight, and how quickly your liver processes the medication, Jeffrey Zipper, MD, chief medical officer at iRecovery USA in Boca Raton, Florida, tells WebMD Connect to Care. “The pain relief and feel-good effects of codeine usually begin 30 to 45 minutes after taking the substance,” Zipper says.