As an Irish citizen, your right to live in the EU/EEA under DIRECTIVE 2004/38/EC can only be denied for very serious, very specific suspicions that you are a present danger to public order and safety. A past criminal record for drugs won't be nearly enough unless there is more in your record we don't know.
Your right to work may be limited where it comes to jobs that require a background check or security clearance. An employer may not want to hire you and hand you the keys to the cash register. We can't answer that question, but any restrictions for you would be the same as for citizens with a similar record.
For that, ask on Expatriates Stack Exchange or possibly on Workplace. When it comes to information exchange, remember that lying on an employment form can be reason for firing if it comes out years later. If the employer is allowed to ask, you are required to answer truthfully.