How can I tell if a work colleague is misusing drugs?

Signs of drug misuse include:

• Sudden mood changes.
• Unusual irritability or aggression.
• Confusion.
• Unusual changes in concentration and energy.
• Impaired job performance.
• Being late for work.
• Taking more time off sick.
• Worsening relationships with colleagues or customers.
• Dishonesty and theft.

Remember that all these could be signs of other problems, including stress.