Andrew Chan, the Australian Christian who was executed in Indonesia this week, wrote a letter before his death warning young people of the dangers of drugs.

Chan read the six-page letter titled "Dear Me" in a documentary made available for schools in the UK and Australia. It's hoped that it will be used as a resource to encourage teenagers not to get involved with drugs.

"Dear Me, when you are older you will be in a Bali prison and you will be executed. This happened to you because you thought taking drugs was cool. Your drug taking made you think that it was OK to import drugs and make money from this. Your family and friends are heart broken and your life will be ended by a firing squad. Underneath you are not a bad person but drugs makes you different. My name is Andrew Chan," the letter, written over a year ago, begins.

"At the end of the day, I'm only 29 years old and, the truth is, I might not be able to see my 30th birthday. How many of you want to follow in my footsteps? And I hope these words will penetrate through your minds and in your hearts and that most of you, if not all of you, will achieve more than I ever did."

Chan was convicted in 2006 of co-leading a drug-smuggling ring known as the Bali Nine, and sentenced to death. He was executed by firing squad along with seven others, including his co-leader Myuran Sukumaran, in the early hours of Wednesday morning. He was 31.

In his letter, Chan said he'd seen many friends die as a result of their addictions. "I'm sure if they had a second chance to do things differently now, they would have."

"I have missed weddings, funerals, just the simple presence of my family. The hurt and pain that I don't just put onto myself but my family is agonising. A simple touch such as a hug is not possible for a condemned man like me," he wrote.

"I have nothing but an iron bar to hug rather than to be embraced by those I love and who I miss. Most likely, I won't have the chance to see such things such as the birth of my first child, let alone have a child.

"My life is a perfect example of an absolute waste. That does not have to be for you."

Chan converted to Christianity in prison, studied theology and was eventually ordained a minister earlier this year. He married his fiancée, Febyanti Herewila, two days before his execution.

In prison, he and Sukumaran established a drug rehabilitation programme and they were described as model inmates by guards. Chan ran Bible studies and led other prisoners to faith, and after receiving 72 hours' notice of their death sentence on Saturday, the international community scrambled to implore the Indonesian government to grant clemency for all nine. Only one execution was called off, however. Mary Jane Fiesta Veloso, a Filipino woman, was granted a temporary reprieve, but the other eight were fatally shot at 12.35am on Wednesday morning.

According to witnesses, they refused blindfolds and sang hymns including Amazing Grace as they faced their executors.

Prime Minister Tony Abbott branded the executions "cruel and unnecessary" and has withdrawn Australia's ambassador from Indonesia.