The measures are aimed at tackling irresponsible drinking
A ban on promotions such as "all you can drink for £10" and "dentist chairs" - a game where alcohol is forced into a customer's mouth - has come into force.
The mandatory code also forbids "speed drinking" competitions and women-drink-free deals, and forces pubs and bars to offer customers free tap water.
Ministers hope it will reduce crime attributed to binge drinking, which it says costs the UK up to £13bn a year.
Offenders could lose licences, be fined up to £20,000 or jailed for six months.
Further conditions to come into effect on 1 October include ensuring all licensed premises offer small measures of beers, wine and spirits and have policies to check the age of anyone who looks under 18.
Home Office Minister Alan Campbell said: "While the vast majority of retailers are responsible, a minority continue to run irresponsible promotions which fuel the excessive drinking that leads to alcohol-related crime and disorder.
"The code will see an end to these promotions and ensure premises check the ID of those who appear to be underage, helping to make our towns and city centres safer places for those who just want to enjoy a good night out."
The code was drawn up with the drinks industry after more than 7,000 people responded to a nationwide consultation in 2008.
Charlotte Elmer, of drinks firm Heineken UK, said this had helped ensure the final version of the code was "proportionate".
"We do not believe... deep discounting to drive footfall sits side-by-side with the promotion of responsible consumption."
However, the British Beer and Pub Association has said legislation should also apply to supermarkets, which it says supply 70% of alcohol sold in the UK.
Home Secretary Alan Johnson announced the measures in January, saying that a voluntary code had failed to tackle binge drinking.
The Conservatives had said they would prefer giving councils the power to charge levies on venues causing problems late at night, increasing duty on specific drinks - such as some very strong beers or alcopops - and permanently shutting problem pubs.
The Liberal Democrats wanted to set a minimum price for alcohol and operate a "one-strike-and-you're-out" policy, with shop owners being fined and losing their licence the first time they are caught selling alcohol to children.
As well as the new mandatory code, the government also introduced Drinking Banning Orders from 1 April, in 25 areas.
They will allow magistrates to ban or prevent an individual who has committed a crime under the influence of alcohol, from entering any premises that sell alcohol.