As the trials continue in the mass-tort litigation brought by American veterans against 3M over its Combat Arms Earplug Version 2 (CAEv2), one issue on both sides’ minds is this: can plaintiffs prove that 3M’s earplug ruined their hearing, and not some other cause?

Before diving into the legal issues, a brief overview of how hearing loss happens is necessary. There are two types of hearing loss: conductive and sensorineural. Only “sensorineural” hearing loss – which can’t be fixed with hearing aids – matters for this litigation. “Conductive” hearing loss occurs when the eardrum physically can’t catch sound– for example, if the eardrum is punctured or the ear is missing. “Sensorineural” hearing loss means that the eardrum catches sound, but the sound isn’t correctly transmitted to the brain. This usually occurs because the hair cells in the cochlea that send sound through your nerves to the brain are damaged – sometimes because of causes like aging or head injuries. Meanwhile, tinnitus – a ringing in the ears – occurs where the brain receives nerve signals from sound when no actual sound happens.

One other potential cause of sensorineural hearing loss and tinnitus is the use of “ototoxic” drugs – drugs that are toxic “to the ear.” This matters because veterans seeking to recover from 3M must show that 3M’s product caused their injuries – which means that 3M can escape liability by showing that something else (like ototoxic drugs) caused a plaintiff’s hearing loss. Because some ototoxic drugs are also viewed negatively by a potential jury – such as marijuana, amphetamines, or Vicodin – 3M’s argument that use of these drugs was medically relevant was relevant risked potential jury prejudice against plaintiffs with a prior history of drug addiction.

In an order issued August 17, 2020, the Court held that 3M could demand medical records showing plaintiffs’ usage of certain drugs potentially associated with hearing loss. These drugs include aminoglycosides (antibiotics used to treat staph and tuberculosis), antineoplastics (anti-cancer drugs which contain platinum), and the non-steroidal anti-inflammation drug (NSAID) Naproxen (sold under brands like Aleve or Vimovo). The Court found that certain other ototoxic drugs that caused reversible hearing loss could be relevant to 3M’s defenses – but weren’t necessarily relevant. These drugs include loop diuretics (used to treat hypertension from heart or kidney problems), macrolides (antibiotics used to treat chlamydia, among other things), NSAIDs other than naproxen (over-the-counter pain medications like Advil/ibuprofen, or Bayer/aspirin), and quinine (used to treat malaria). With respect to these drugs, the Court required 3M to show that a plaintiff used the drug when diagnosed with hearing loss or tinnitus, and that the plaintiff still uses the drug. The same rules apply to marijuana or amphetamine use, if a plaintiff used marijuana or amphetamines at least monthly for 12 months before diagnosis with tinnitus while using marijuana, or with hearing loss while using amphetamines – but not the other way around.

Veterans interested by the ongoing bellwether trial against 3M should bear this causation issue in mind – with billions of dollars at stake in this massive lawsuit, 3M may intensely question claimants in hopes of finding some cause to blame besides their CAEv2 earplugs.