What to do if your friend is unconscious from drugs?

call the ambulance

Always a good start, while you're waiting stay with them and make sure they are breathing, put them in the recovery position so if they vomit their air way will the clear.

Do not panic. It will only make things worse, you need to keep a clear head and be there for your friend. If here are other friends around, find out what they took, it might help they emergency team if they know what they're dealing with.