Uruguay last year became the first country in the world to make it legal to grow, sell and consume marijuana.
The law allows registered Uruguayans over 18 to buy up to 40g of the drug every month and is aimed at tackling the power of drug cartels.
In 2012, American voters in Colorado and Washington State backed laws which legalised the recreational use of cannabis.
Long queues formed as the first state-licensed cannabis outlets in Colorado opened their doors in January.
That month, the state made £1.2 million in taxes from cannabis sales.
In Holland, cannabis has never been formally legalised, however the purchase and consumption of small amounts of the drug have been informally permitted since 1976. There are about 700 licensed coffee shops which sell cannabis in the country.