## Facts

- Laura Doull received care from nurse practitioner Anna C. Foster at a medical practice owned by Foster’s supervising physician, Dr. Richard J. Miller, from 2008 to 2011.
- Foster prescribed a topically applied, “naturally derived” progesterone cream for perimenopausal symptoms.
- Foster did not document any discussion of the cream’s risks, benefits, or alternatives; she testified that alternatives were discussed and that she did not discuss clotting risk because she did not view it as a risk.
- In spring 2011, Doull repeatedly reported shortness of breath during visits to the practice; Foster treated her for asthma/allergies, and Miller did not examine her.
- In May 2011, Doull was hospitalized after a seizure-like event and was diagnosed with pulmonary embolism and chronic thromboembolic pulmonary hypertension (CTEPH).
- Doull died in 2015 from complications of CTEPH.
- Plaintiffs alleged the progesterone cream caused blood clots and that defendants’ failures in diagnosis and supervision caused or worsened Doull’s condition; defendants disputed both the clotting risk and causal connection.

## Issues

1. Whether a medical malpractice jury should be instructed on “substantial contributing factor” causation, rather than only traditional but-for causation, when multiple alleged causes are present.
2. Whether the trial judge’s instructions on standard of care, breach, and causation were erroneous or misleading.
3. Whether asserted trial-management errors (including denial of amendment, informed-consent instruction issues, and limits on juror contact) required a new trial.

## Decision

- The Supreme Judicial Court affirmed the judgment for defendants and affirmed denial of plaintiffs’ motion for a new trial.
- The court held that traditional but-for factual causation is the proper standard in most negligence cases, including those involving multiple alleged causes.
- The court discontinued use of the “substantial factor” test in Massachusetts jury instructions, including in multiple sufficient-cause contexts, as unnecessarily confusing.
- The trial court properly instructed on but-for causation; plaintiffs’ additional claims of error did not warrant relief.

## Legal Principles

- Factual causation in negligence is generally established by proving the harm would not have occurred absent the defendant’s negligent conduct (but-for causation).
- “Substantial factor” language is disfavored because it can conflate factual causation with scope-of-liability (proximate cause) concepts and can be understood as allowing liability without but-for proof.
- Multiple-cause cases ordinarily remain subject to but-for analysis; exceptional causal patterns should be handled through explicit, carefully defined rules rather than a generic “substantial factor” instruction.
- Trial judges have discretion over complaint amendments and post-verdict juror-contact restrictions, and appellate relief requires a showing of legal error and prejudice.

## Conclusion

Massachusetts clarified that but-for causation governs most negligence and medical malpractice cases and eliminated “substantial factor” causation instructions as confusing; applying that rule, the court upheld the defense verdict where the jury found negligence but no causation.


Doull v. Foster, 487 Mass. 1, 163 N.E.3d 976 (Mass. 2021)