Conditional discharge or not, it was still related to a conviction, which is all that US law is interested in.
The US Immigration and Nationality Act states:
"any alien convicted of, or who admits having committed, or who admits committing acts which constitute the essential elements of . . . a violation of (or a conspiracy or attempt to violate) any law or regulation of a State, the United States, or a foreign country relating to a controlled substance . . . is inadmissible".
The only exceptions to that rule are
(i) when the offender was under 18 at the time of the offence AND more than 5 years has passed since that date ; OR
(ii) when the maximum penalty for the offence does not exceed one year's imprisonment. (Note that it's the maximum penalty which COULD have been imposed which is relevant, not the penalty which was ACTUALLY imposed. The maximum penalty for possession of a Class B drug, such as cannabis, is 5 years imprisonment).
So you're almost certainly barred from entering the USA. However that's not the end of the story. You can apply for a 'waiver of ineligibility' but, if you do so, be prepared for a lot of hassle and a very long wait. (The longest wait I've seen reported here on AB was a guy who waited 15 months before having his visa application rejected. He'd committed 2 offences of driving with no insurance).
Chris