Laudanum is a tincture of opium containing approximately 10% powdered opium by weight (the equivalent of 1% morphine). Laudanum is prepared by dissolving extracts from the opium poppy (Papaver somniferum) in alcohol (ethanol).

Reddish-brown in color and extremely bitter, laudanum contains several opium alkaloids, including morphine and codeine. Laudanum was historically used to treat a variety of conditions, but its principal use was as a pain medication and cough suppressant. Until the early 20th century, laudanum was sold without a prescription and was a constituent of many patent medicines. Today, laudanum is recognized as addictive and is strictly regulated and controlled as such throughout most of the world. The United States Controlled Substances Act, for one example, lists it on Schedule II, the second strictest category.

Laudanum is known as a "whole opium" preparation since it historically contained all the alkaloids found in the opium poppy, which are extracted from the dried latex of ripe seed pods (Papaver somniferum L., succus siccum). Today, however, the drug is often processed to remove all or most of the noscapine (also called narcotine) present as this is a strong emetic and does not add appreciably to the analgesic or antipropulsive properties of opium; the resulting solution is called Denarcotized Tincture of Opium or Deodorized Tincture of Opium (DTO).

Laudanum remains available by prescription in the United States (under the generic name "opium tincture") and in the European Union and United Kingdom (under the trade name Dropizol), although today the drug's therapeutic indication is generally limited to controlling diarrhea when other medications have failed.

The terms laudanum and tincture of opium are generally interchangeable, but in contemporary medical practice, the latter is used almost exclusively.