Discovery regarding expert witnesses can be tricky. In our neck of the woods, the great Commonwealth of Pennsylvania, state courts almost never permit depositions of experts. If you want to ask the expert questions – and you will – you must wait until trial. The flip side of that restriction is that expert reports in Pennsylvania must really and truly and completely disclose the expert’s opinion. If an expert at trial strays a millimeter past the four corners of the expert report, the court will shut such testimony down. By contrast, in most court systems, including the federal system, discovery regarding expert witnesses is extensive, and the deposition of the other side’s expert is usually one of the most consequential moments in the litigation.

Mind you, we are talking about testifying experts. Parties can retain experts who will testify at trial, but they can also retain experts who serve purely as consultants. Those consulting experts work behind the scenes, furnishing facts and ideas. They might, for example, help us prepare to depose the other side’s experts. These consulting experts are usually not subjected to the discovery maw.

But what if an expert transforms from consultant to testifier in the course of a litigation? What and how much is discoverable? That interesting scenario arose in In Re: Abilify (Aripiprazole) Prods. Liab. Litig., 2017 U.S. Dist. LEXIS 73847 (N.D. Fla. May 15, 2017). The plaintiff lawyers talked to an expert “informally,” then later retained him. That expert had conducted research, resulting in an article, upon which the plaintiffs then relied. The defendants sought to depose that expert about the article, including whether the plaintiff lawyers influenced the study. The defense did not want the plaintiffs’ expert to point proudly to a peer reviewed study if the plaintiff lawyers had done as much reviewing as the peers.

As you can imagine, the plaintiff lawyers resisted. They argued that questions about the inputs into the article would have a chilling effect on scientific research. The plaintiffs object to any discovery into communications between the expert and plaintiffs’ counsel because Fed. R. Civ. P. 26(b)(4)(D) protects informal consultation with experts: “Ordinarily, a party may not, by interrogatories or deposition discovery facts known or opinions held by an expert who has been retained or specially employed by another party in anticipation of litigation or to prepare for trial and who is not expected to be called as a witness at trial” except on a “showing [of] exceptional circumstances under which it is impracticable for the party to obtain facts or opinions on the same subject by other means.” The plaintiffs also objected because communications with the expert were protected opinion work product under Fed. R. Civ. P. 26(b)(3): the court “must protect against disclosure of mental impressions, conclusions, opinions, or legal theories of a party’s attorney or other representative concerning the litigation.”

The court allowed some discovery, but within limits. The court held that the defendants could question the expert about the plaintiffs’ influence on the study, as it is an aspect of bias. Even if the influence occurred during the “informal” consultant period, it was fair game. Thus, the defendants were permitted to inquire whether the expert “made any changes to the timing, methodology, or other relevant aspect of the study following communications with Plaintiffs’ counsel.” Further, to the extent that the expert “initiated contact with Plaintiffs’ counsel, Defendants are free to inquire into his motive and the timing of such contact.” But the court also held that the defendants could not inquire into work product (“regarding any opinions or case strategies shared by Plaintiffs’ counsel, or any other inquiries made by plaintiffs’ counsel that related to the preparation of their case”) unless the deposition established that the plaintiffs influenced the conduct of the study. If evidence of the plaintiffs’ lawyers inputs into the study surfaces during the deposition, the parties would need to contact the Judge to determine whether a waiver of work product had taken place.

This case is not really a ‘win’ for plaintiffs or defendants, because the court’s decision threads the needle fairly carefully, and because, considering the rule from an ex ante perspective, both plaintiffs and defendants might retain consulting experts who later become testifiers. Rather, the case represents an unusual, but not impossible, situation where both sides must be especially careful.