Medical Science Liaisons occupy a structurally unusual position in pharma — they’re the scientific face of the company in the field, operating under medical affairs governance but serving commercial objectives, expected to have peer-level scientific conversations with KOLs while maintaining the separation from promotional messaging that gives them credibility in the first place. The best MSL teams understand this tension and use it strategically. The average ones default to presenting slides and calling it scientific exchange.
The Distinction That Matters: Reactive vs. Proactive Scientific Engagement
Reactive MSL engagement is responding to unsolicited questions from HCPs about approved products and pipeline assets. This is table stakes — any MSL program can do it. Proactive engagement means identifying the scientific questions and clinical gaps that matter to your highest-priority KOLs and building a sustained program to engage around those questions — before the promotional team is anywhere near those conversations.
The best MSL teams map the scientific landscape of their disease area from the KOL’s perspective: what are the unresolved questions in the literature, what data are KOLs most skeptical of, what clinical scenarios create genuine uncertainty that better evidence could resolve? MSLs who show up with answers to those questions — rather than with a presentation built around the company’s data package — build the kind of scientific relationships that translate into advisory board participation, investigator-initiated study interest, and genuine advocacy when payers and guideline committees form their views.
Territory Management: Not All KOLs Are Equal
MSL territories are typically geographic, but scientific influence doesn’t distribute geographically. A KOL at a major academic medical center may influence prescribing patterns across an entire region through their publications, presentations, and informal peer network. An MSL who spends equal time across their territory geography — rather than disproportionate time with the highest-influence scientists — is optimizing for coverage metrics, not scientific impact.
The highest-performing MSL programs tier their key accounts by scientific influence, not just prescribing volume. KOLs who are generating primary data, speaking at major congresses, and participating in guidelines committees get a different engagement model than prescribers who are early adopters but not scientific influencers. This tiering drives resource allocation, not just call frequency targets.
The MSL-Commercial Firewall: How to Navigate It Without Violating It
The regulatory separation between medical affairs and commercial is real and important — MSLs cannot be directed by commercial teams or used as an extension of the sales force. But the best MSL programs are aligned with commercial strategy even when they’re not directed by commercial. They’re engaging around the scientific questions that matter most for the brand’s commercial position: the clinical scenarios where the drug’s data are most compelling, the comparative effectiveness questions that are driving payer skepticism, the real-world evidence gaps that advisory boards are flagging.
Medical Affairs leaders who treat commercial alignment as a compliance risk rather than a strategic imperative are leaving impact on the table. The firewall is about direction and incentives, not about strategic coordination on which scientific questions to prioritize.
Measuring MSL Impact
MSL programs are notoriously difficult to measure, and many settle for activity metrics — number of interactions, HCP satisfaction scores — that measure effort rather than impact. The metrics that matter for strategic MSL programs are: quality of advisory board scientific exchange, investigator-initiated study proposal rate, KOL willingness to present at company-sponsored educational programs, and consistency of scientific messaging in publications and presentations by engaged KOLs.
None of these are easy to quantify, which is why most teams default to call counts. The teams that build the qualitative measurement frameworks — and hold MSLs accountable for scientific relationship depth, not just activity volume — consistently outperform those that don’t.
Related: HCP Engagement & Medical Affairs Hub
