These style of questions, like "are you of have you ever been a member of the Nazi Party or Communist Party?", are there to give a blanket reason for revocation of visa and instant deportation for providing false information on the form if it can be shown you did lie on the tick boxes.
If you have never been convicted or arrested, and not blasted out of your noggin at the border, then say No.
Is the question, "have you ever used illegal drugs" part of a long list of questions presented together? If so, it’s what I call a "no list"; if you know what’s good for you you will answer "no" to them all, every time. As a general rule, they have no way of knowing what you actually did, unless of course you answered "yes". (If they do see a "yes" they will start asking a lot more questions in that area.)
As a backup, make up a story that explains why "no" is really the correct answer, something along the lines of "but I didn’t inhale". If it comes down to it, you don’t need to convince them of anything except that you didn’t think you weren’t intentionally lying.
I don’t know if there is an answer for "anglophone nations" in general—countries make their own laws and these laws can differ even when they share a common language or colonial history—but in the specific case of the United States, 8 USC § 1182(a)(1)(A)(iv) prohibits anyone "who is determined (in accordance with regulations prescribed by the Secretary of Health and Human Services) to be a drug abuser or addict" from entering the country, even if that person has not been convicted of any crimes in any country. Part (a)(2)(A)(i)(II) of the same section prohibits anyone who "admits having committed…a violation of any law…relating to a controlled substance," again without any requirement for a charge or conviction of such a violation.
It may not surprise you to learn that US officials, at least sometimes, interpret these rules rather broadly, and occasionally deny entry to people who merely admit past marijuana use, even in countries where this is legal.
There are additional further restrictions on people who have been convicted of drug trafficking or other crimes, but this doesn’t seem to be the main focus of your question.
Credit:stackoverflow.com‘