What Is Causation in a Personal Injury Case?

James Wong — Founder & Pharmacist, LienScripts | March 25, 2024 | 7 min read

Causation is the legal and clinical requirement that connects a defendant's negligence to the plaintiff's injuries and treatment. In personal injury cases, pharmacy records and clinical narratives are among the most effective tools for establishing and defending causation.

This post is for informational purposes only and does not constitute legal advice.

The Link That Holds the Case Together

Every personal injury case rests on four elements: duty, breach, causation, and damages. Of these, causation is the one most frequently attacked by defense counsel and insurance adjusters — because it is where the clinical record either supports the case or exposes its weaknesses.

Causation requires proof that the defendant's negligent act was the cause of the plaintiff's injuries and the resulting need for treatment. Without causation, damages are just numbers — there is no legal basis for the defendant to pay them.

[!KEY] Causation in a PI case must be proved medication by medication — each prescription in the lien must be traceable to the injury through prescription dates, diagnosis codes, and the treating physician's clinical record.

For pharmacy-heavy PI cases, causation is established medication by medication. Each prescription in the claim must be traceable to the injury. That traceability is what makes pharmacy documentation so critical to case value.

Legal vs. Clinical Causation

Causation operates on two levels in a PI case.

Legal causation is the "but for" test: but for the defendant's act, the plaintiff would not have been injured. A car that rear-ended your client at a red light is the legal cause of the resulting neck injury. This level of causation is typically straightforward in motor vehicle accident cases.

Clinical causation is more nuanced: it asks whether the specific medical treatment the plaintiff received — including every prescription filled — was medically necessary and caused by the injury at issue, not by a pre-existing condition or unrelated health issue.

This is where defense adjusters focus their attacks. An adjuster who cannot dispute the accident itself will look for ways to argue that:

• The plaintiff's treatment was excessive for the severity of the injury.
• A pre-existing condition explains the need for medication, not the accident.
• The medications were prescribed for unrelated conditions.
• The treatment timeline doesn't match the expected recovery curve.

How Pharmacy Records Establish Causation

A well-documented pharmacy lien record creates a causation timeline that is difficult to attack. Each fill has a prescription date, a prescribing physician, a diagnosed condition, and a dispense date. Together, they trace a clinical narrative from accident to treatment to outcome.

Key elements of causation-supporting pharmacy documentation:

Prescriber identity. Prescriptions written by treating physicians — orthopedists, neurologists, pain management specialists — connected to the injury carry more causation weight than prescriptions written by providers unrelated to the injury.

Prescription timing. Fills that begin shortly after the accident and correspond to the expected treatment arc for that injury type are harder to challenge than medications that start months after the accident with no clear clinical transition.

Diagnosis codes. Pharmacy records include the ICD-10 diagnosis codes associated with each prescription. Codes corresponding to injury diagnoses — whiplash, lumbar strain, neuropathy — connect each medication directly to the injury.

Treatment continuity. A consistent medication regimen without unexplained gaps is a stronger causation record than a sporadic fill history with months of non-compliance.

The MERIT Report as a Causation Document

LienScripts generates MERIT reports (Pharmacy Outcome and Goals of Service) that function as clinical causation narratives. A MERIT report goes beyond raw dispensing data to explain:

• Why each medication was prescribed for this specific injury.
• What clinical goals the medication was intended to achieve.
• What outcomes were observed during the treatment period.
• How the medication regimen evolved as the case progressed.

For attorneys building a demand package or preparing for mediation, the MERIT report is the document that converts a list of drug names into a clinical story. It anticipates causation challenges and addresses them before the adjuster raises them.

[!KEY] The MERIT report is a causation document, not just a billing document — it narrates why each medication was prescribed, what injury it was treating, and how the regimen evolved as the case progressed, making it the most effective pre-litigation counter to every standard adjuster attack on medical necessity.

See our post on using the MERIT report at settlement conferences for more detail on how MERIT documentation is used strategically.

When Insurance Adjusters Attack Causation

The most common causation attacks in PI cases involving pharmacy liens:

"These medications treat pre-existing conditions." Response: Review the prescription record for any medications predating the accident. If the client had no prior prescriptions for these drugs, the record itself refutes the argument. The MERIT report can document the absence of pre-existing use.

"The treatment was excessive." Response: The clinical evidence standard — not the adjuster's opinion — governs medical necessity. A medical necessity determination by the prescribing physician, supported by pharmacy records and clinical notes, carries more weight than an adjuster's peer review.

"The medications aren't connected to this accident." Response: Diagnosis codes, prescriber notes, and treatment timelines directly linking each drug to the injury diagnosis are the response. This is where having organized, complete pharmacy records from a lien administrator like LienScripts makes a material difference.

"The client stopped treatment and then restarted." Response: Treatment gaps can be explained clinically — insurance denial, prescription change, clinical progress followed by setback. The pharmacy record and a MERIT narrative can document each transition.

[!TIP] For Attorneys: The MERIT report from LienScripts functions as a clinical causation document — it anticipates every common adjuster attack on medical necessity and addresses them before they are raised in settlement negotiations.

Strengthening Causation With a Medication Timeline

One practical tool for attorneys: organize the pharmacy record into a medication timeline that maps each prescription to a point in the injury and recovery arc. Include:

• Date of accident
• First medical visit and diagnosis
• First prescription fills and corresponding diagnoses
• Any treatment changes tied to clinical developments (surgery, specialist referral, etc.)
• Treatment conclusion or transition to chronic management

This timeline becomes a visual causation argument. It shows the progression from injury to treatment to outcome in a format that mediators, adjusters, and jurors can follow.

LienScripts' LSR (Lien Summary Report) provides the raw medication timeline in organized form. When combined with a MERIT narrative, it provides both the financial record and the clinical causation story.

[!KEY] An adjuster who claims that a specific medication was pre-existing can be countered with a single piece of evidence: the pharmacy record showing the first fill date for that drug, which was after the accident date — a fact that requires no expert testimony and is impossible to fabricate.

Key Takeaway

Causation is the thread that connects every prescription to the defendant's negligence. Without a clear, documented causal chain from accident to treatment to pharmacy record, lien amounts are vulnerable to challenge. Organized pharmacy documentation — including LSRs and MERIT reports — is the most effective tool available to PI attorneys for establishing and defending causation in medication-heavy cases.