Someone is making a false accusation about a friend of mine, can he take legal action?

My friend has been falsely accused of taking a bottle of medication from a function he attended. The reason they have blamed him is because as a nurse they believe he was the only person at the function that would have any knowledge of the fact that that medication is highly sought after by recreational drug users. There is no other 'evidence' to suggest that he took it. He states that as a nurse he knows better than to take any type of medication that is not prescribed specifically for him and knows better than to use illicit/recreational drugs. He is willing to undergo testing to prove he hasn't taken it. He would like to take legal action because this situation has caused him much stress and implies things about him that are not true. He is concerned because as a nurse his reputation and career could be destroyed with this sort of allegation. Is there any thing he can do?