Stelios Tzellos | What Most People Get Wrong About Pharmaceutical Consulting
Stelios Tzellos
Ask someone outside the industry what pharmaceutical consulting looks like and they'll probably picture someone in a suit presenting slides to executives. Ask someone inside the industry and you'll get a different answer: it's long hours building models that clients will use for decisions worth hundreds of millions of dollars, and hoping the assumptions hold.
Stelios Tzellos of the UK spent years in pharmaceutical consulting at GlobalData and IQVIA before moving to AstraZeneca. His career offers a clear view of what consulting in life sciences actually involves, and why most outsiders and even some insiders misunderstand the work.
It's Not About the Slides
The deliverable in pharmaceutical consulting is almost always a report or a model. But the value isn't in the document itself. It's in the thinking that produces it. A good consultant in this space needs to understand the disease area, the competitive dynamics, the regulatory environment, and the commercial context well enough to make assumptions that will still be valid in twelve months.
Tzellos started at GlobalData as a healthcare analyst focused on oncology and haematology. He built epidemiology models, produced competitive assessments, and developed market forecasts for cancer indications. That work required deep engagement with the subject matter. You can't model the Hodgkin's lymphoma market by pulling numbers from a database. You need to understand treatment algorithms, patient subpopulations, and how new therapies are likely to change physician behavior.
That's the part most people miss. Pharmaceutical consulting isn't about applying a standard methodology to a new dataset. It's about understanding the context well enough to know when the standard methodology doesn't apply.
The IQVIA Difference
Moving from GlobalData to IQVIA, Stelios Tzellos advanced into oncology disease insights and the Analytics Center of Excellence. IQVIA sits at a unique position in the industry: it has access to more pharmaceutical data than almost any other organization. The challenge is turning that data into insights that clients can actually use.
Tzellos worked with global pharmaceutical clients on forecasting, commercial planning, and evidence-based strategy. The best client engagements were the ones where the consulting team and the client team worked as genuine partners. The worst were the ones where the client handed over a brief and expected a finished product without iteration.
Pharmaceutical markets move too fast for that kind of handoff to work. By the time a consulting project wraps up, a new clinical readout might have changed the competitive picture. The consultants who deliver the most value are the ones who build flexibility into their models and maintain an ongoing relationship with the science.
Why He Left Consulting for Industry
Tzellos joined AstraZeneca in 2020, moving from the consulting side to the industry side of pharmaceutical analytics. The shift made sense for someone whose interests span business insights, analytics, and oncology marketing. Inside a pharmaceutical company, you get to see whether the work you did as a consultant actually influenced decisions.
That feedback loop matters. In consulting, you hand over a forecast and move on to the next project. In industry, you live with the consequences of that forecast. You see where it was right and where it was wrong, and you learn from both.
At AstraZeneca, Tzellos leads cross-functional projects that support product strategy, market planning, and portfolio decision making. The consulting skills translate directly: the ability to synthesize information, build evidence-based arguments, and present complex analyses to senior leadership. What changes is the perspective.
The Value of Having Done Both
Stelios Tzellos holds degrees in Biochemistry and Molecular Biology from Imperial College London. His academic training gave him scientific depth. His consulting career at GlobalData and IQVIA gave him commercial breadth. And his current role at AstraZeneca gives him the chance to apply both.
The pharmaceutical industry benefits most from people who have worked on multiple sides of the business. Consulting teaches you to think broadly and deliver under pressure. Industry teaches you to think deeply and live with your recommendations. The people who have done both bring a perspective that neither experience alone provides.
If you're considering a career in pharmaceutical consulting, know this: the work is harder, more complex, and more consequential than it looks from the outside. And the best consultants are the ones who understand the science as well as they understand the business.