What are yellow Xanax bars R039? | 4 followers on LinkedIn. What are yellow Xanax bars R039? ro39 xanax yellow 2mg xanax bars r039 yellow bar xanax r039 strength yellow pill r039 | What are yellow Xanax bars R039? Yellow Xanax bars R039 (active substance Alprazolam) are a vivid representative of the anti-anxiety class of medicines. They belong to the new generation derivatives of benzodiazepines that work in the brain to deal with anxiety.